USMLE Step 2 CK Medical Subject Review: Pediatrics

A 2-week-old male infant presents with a 1-day history of loose stools, vomiting, and refusal to feed. He is passing less urine than he did in the morning. Birth weight was 2.8 kg. Physical examination reveals that the infant is lethargic with signs of dehydration. Anterior fontanelle is depressed; heart rate is 180/min; BP is 54/34 mm Hg; respiratory rate is 76/min. Capillary refilling time is 5 seconds. Abdominal examination is normal. Blood examination shows Hemoglobin 16 gm/dL, total leukocyte count is 12,400/mm3, polymorphs 62%, lymphocytes 34%, eosinophils 2%, monocytes 2%, and CRP-negative. Serum sodium 120 mEq/L, potassium 6.8 mEq/L, blood urea 3.5 mg/dL, creatinine 0.8 mg/dL, bicarbonate 15 mEq/L, and platelet count 200,000/mm3. Urinalysis shows brownish granular casts, urinary osmolality of 295 mOsmol/kg, and urinary sodium of 65 mEq/L. What is the most likely diagnosis?

Acute tubular necrosis

A 38-year-old previously healthy woman who is 10 weeks pregnant with her first child presents with fatigue and lightheadedness. She has had emesis throughout the day for the past 2 weeks and has had trouble keeping food and liquids in her stomach. Physical exam shows a temperature of 37°C (98.6°F), a sitting blood pressure of 100/60 mm Hg, and a standing pressure of 82/42 mm Hg. Her skin turgor is poor and her mucus membranes are dry, but the remainder of her exam is normal. Her diagnostic tests include: Urinalysis: Few ccs of yellow-brown urine, no blood, no cells, trace glucose, no protein. 2 muddy casts No bacteria Serum creatinine: 1.4 mg/dl Serum potassium: 4.0 meq/l Serum bicarbonate: 27 meq/l Serum glucose: 60 mg/dl Total white blood cell count: 5x103/mm3 What is the most likely cause of her renal findings?

Acute tubular necrosis

8-year-old girl presents with her mother to the pediatrician's office with persistent clear nasal drainage and nighttime cough for the past month. Her physical examination reveals clear rhinorrhea, dark circles under her eyes, and a transverse nasal crease. What is the most likely diagnosis?

Allergic rhinitis

11-year-old girl with hair loss, presents to the clinic with her mom. The girl noticed her hair thinning and a bald spot on her scalp. She reports having atopy, denies feeling recently stressed, and does not report any underlying disorders. Upon physical exam, her hair does appear thin. The bald spot is smooth and round. Around its border there are short, broken off hairs which appear narrower closer to the scalp. Her mom states that she also had an issue with hair thinning when she was her daughter's age. All laboratory finding are within normal limits. What is the most likely diagnosis?

Alopecia areata

12-year-old boy is brought in to his pediatrician's office due to ear pain, nasal congestion, decreased hearing, and sore throat. He was well until about 2 days ago when he began to have ear fullness. The pain began last night and did not improve when treated with over-the-counter analgesics. Physical exam revealed bilateral bulging of the tympanic membranes with erythema, bullae, and decreased mobility with pneumatic otoscopy. Vital signs are as follows: Blood pressure 106/72 mm Hg, Pulse 68/min, Respiratory Rate 12 per minute, Temp 102.1 degrees Fahrenheit. The initial antibiotic of choice for this patient is:

Amoxicillin

1-year-old boy is brought in by his dad with a "finger infection." About 10 days ago, the child was bit by a pet rat on his index finger. They did not think anything of it until few days ago, which is when the finger became swollen and the child started to appear unwell. He presents with increased temperatures, decreased appetite, and vomiting. His vital signs are normal, except for temperature, which was 102°F. He was hydrated with IV fluids, and empiric antibiotics were started. Blood cultures were taken, and the causative organism was identified as S. minus. The child is getting moderate oral intake at this time. What is the most appropriate treatment for this infection?

Amoxicillin/clavulanic acid

A 20-month-old boy presents for a routine visit. He is eating well and drinking at least a bottle of cow's milk daily, which he has done since age 8 months. His history and physical are normal except for mild pallor. Urinalysis is normal. Result Normal Values Hemoglobin 9.5 10.5-14.0 g/dL RDW 52 38.5-49.0% MCV 72 76.0-90.0 fl Platelets 280,000 150,000-450,000/μL WBC 6.7 5000-14,500/μL What additional finding might you expect in this child?

Anisocytosis

A 7-day-old infant is evaluated for feeding intolerance since birth. An orogastric tube is passed easily into the stomach and is visualized on x-ray film. The infant's exam is notable for a soft and non-tender abdomen. MRI demonstrates an extra-luminal mass lesion surrounding that second portion of the duodenum. Which is the most likely diagnosis?

Annular Pancreas

14-year-old female is brought to the Family Medicine Clinic presenting with heavy menses and occasional epistaxis. The mother reports that this is common among the women in their extended family but not investigated until now. Lab values in the preliminary workup include a set of abnormal closure times in the PFA-100 bleeding test device (but not indicative of aspirin effect), a normal PT, slightly prolonged aPTT, normal platelet count, normal fibrinogen, and Hematocrit=32%. A von Willebrand's workup reveals 30% antigen level, 25% ristocetin cofactor activity level, and 40% Factor VIII clotting activity. The patient states that she wants analgesic relief from the discomfort accompanying menstruation and desires an intervention to reduce the episodic bleeding. What is the best set of recommendations you can make to this patient?

Avoid aspirin; use DDAVP (desmopressin) nasal spray at first sign of any excessive bleeding

8-year-old boy has abdominal pain and vomits twice. No fever is noted, and he has not had any diarrhea. On examination the next morning, he presents with diffuse lower abdominal pain with rebound tenderness on the lower right side. On rectal examination, there is no localization. What is the next recommendation?

CBC, UA, and abdominal ultrasound

4-month-old febrile infant presents with loss of appetite, irritability, seizures, focal sensory and motor deficits, and an acute petechial rash. On physical examination, a bulging fontanelle is noted; rectal temperature is 102.8°F. What test would be most helpful in evaluating this patient?

CSF analysis

3-year-old girl presents with a 1-day history of irritability and weakness in her legs. Neurologic exam reveals an ascending symmetrical paralysis with cranial neuropathy. A lumbar puncture is performed and cerebrospinal fluid is found to have a normal glucose level, <10 leukocytes/mm3, and elevated protein. Medical history shows the child recently recovered from a mild diarrheal illness. What organism is triggering this syndrome?

Campylobacter jejuni

4-year-old boy presents with erratic movements of his left arm and leg. These movements have been present since birth and occur on the left side. They have not been getting worse. The boy's mother admits that he has been using his right hand for almost all activities since the age of 1. Further questioning reveals that the child exhibited delayed milestones, such as rolling over at 6 months, sitting up at 1 year, and walking at 2 years. He does not speak, and he does not respond to his mother's verbal commands. His physical exam is noteworthy for spasticity, hyperreflexia, ataxia, involuntary movements, and weakness of his left arm and leg. His left arm and left leg are measured to be shorter and are atrophied in comparison to the right. Additionally, the child does not respond to verbal stimuli. What is the most likely diagnosis?

Cerebral palsy

4-year-old boy presents with a mass in the neck. His mother works as mycobacteriology laboratory personnel. Physical examination of the child reveals non-tender discrete lymph nodes in the upper neck. Oropharyngeal examination is negative; so are the chest X-ray and tuberculin skin test using purified protein derivative (PPD). Cervical lymph node biopsy is advised. Biopsy report shows granulomatous lesion with central necrosis and special stain revealed presence of acid-fast bacilli. Non-reactive PPD test in this child could be due to what?

Cervical lymphadenitis from atypical mycobacteria

A 15-year-old unmarried young woman delivered a healthy 7-pound baby girl. The parent had not received proper prenatal care because she was trying to hide her pregnancy from her parents. She did not inform her nurses of a persistent vaginal discharge she experienced prior to delivery. A week after delivery, the infant's eyes became filled with pus and swollen (see below). The infant also developed a short stuttering cough. Cultures of exfoliated cells from the infant's eyelids grew negative for bacteria. An endocervical swab of the mother was also negative. Microorganisms similar to those found in maternal endocervical scraping, examined by immunofluorescence, were also seen in the infant's conjunctival scrapings. The infant MOST likely has an infection caused by:

Chlamydia trachomatis

2-year-old boy has a solid mass of tumor on the lower pole of his right kidney. Histopathological studies show whorls of mesenchymal cells and clusters of disorganized epithelial cells rather than renal corpuscles and renal tubules, which confirm your suspected diagnosis. What is true regarding treatment and/or prognosis of this diagnosis?

Combination chemotherapy is appropriate after surgery.

2-hour-old, full-term infant who had no prenatal care has developed severe respiratory distress requiring intubation and ventilation. A chest x-ray shown below suggests an abnormality in the left hemithorax. The MOST likely diagnosis is:

Congenital diaphragmatic hernia

A healthy 29-year-old woman, gravida 2 para 1, now in her 8th week of pregnancy, presents for advice. Her 1st pregnancy and delivery were without complication, but the baby weighed 4200 grams. During this pregnancy, she has gained 4 kg and her BMI now is 25. She wants to avoid a 'big baby' in this pregnancy. What is the best primary prevention of fetal overgrowth this patient can use?

Counseling regarding appropriate weight gain

24-hour-old term male newborn presents with jaundice. Birth weight was 2.5 kg, and the infant cried immediately after birth. Physical examination reveals he has severe icterus and no pallor; cry and activity are fair, and there is no hepatosplenomegaly. Tone in the limbs is normal, and neonatal reflexes are elicited. Blood examination shows Hb of 16.5 mg/dL. Serum bilirubin total is 44.5 mg/dL, with a predominance of unconjugated bilirubin. Conjugated bilirubin level is normal. The direct Coombs test is negative. What is the most likely diagnosis?

Crigler-Najjar syndrome type I

Parents are worried because their 10-year-old daughter is constantly gaining weight. It started a few years ago with increasing appetite, and now she is always hungry. At the beginning, her parents were happy because the child had feeding difficulties as a baby. But now they are worried. Besides constantly foraging for food, she demonstrates some other behavioral problems, including compulsive skin picking, temper tantrums, and stubbornness. Her developmental milestones were globally delayed by the first year, and she has mild intellectual disability (IQ 66). The rest of the family and personal history is non-contributing. On examination you note dysmorphic facial features: almond-shaped eyes, narrowing of the head at the temples, small and turned down mouth, and thin upper lip. On physical examination you find morbid obesity: her height is 96 cm and weight 50 kg (BMI: 54,3); her head is small (circumference 42 cm); and she has small hands and feet with hypoplastic nails. Based on a history and physical examination, you think that she might have the imprinting mutation. What method will you use to confirm your diagnosis?

DNA methylation test

Your patient is 4-year-old girl with a 1-day history of eye redness and pain. Slit examination shows corneal ulceration. You also notice many freckles, spidery blood vessels, and dry skin with irregular dark spots, but what worries you the most is shiny, pearly nodule on her left cheek. Blood vessels are crossing its surface and there is a small central ulcer so that the edges of the lesion appear rolled. Her parents say that the nodule often bleeds spontaneously then it seems to heal over. They also report that since birth, her skin is extremely sensitive to sunlight; she gets severe sunburns on any exposure. The child was born on time to consanguineous parents and her prenatal and postnatal history was normal during the first 6 months. After that time, her parents started to notice skin changes and signs of developmental delay. They thought that it was reaction to the influenza vaccine and stopped all immunizations after that. What is the most probable mechanism of the development of skin changes on the cheek of this patient in this age group?

Defective DNA repair

A woman presents with her 2-year-old male child because he had tonic convulsion. She describes that her child is usually sick; he has had recurrent infections since he was born. He also has special facial features: his eyes are separated by a wide space, and he is known to have a congenital heart disease. What is the genetics of the disease in this case?

Deletion of chromosome 22q11

A 19-year-old previously healthy primigravida develops fatigue, increased peripheral edema, and headaches at 37 weeks gestation. Physical exam shows a blood pressure of 160/110 mmHg, bilateral bibasilar crackles, bilateral calf edema, and hyperreflexia. Laboratory studies include: Urinalysis No glucose, no blood, no cells, ++ protein, no casts, no leukocyte esterase, no nitrate Serum creatinine 0.6 mg/dL Serum potassium 4 meq/L Serum bicarbonate 24 meq/L Serum uric acid 10 mg/dL Fetal lung surfactant Positive, suggestive of lung maturity What intervention is indicated?

Delivery

A woman presents to the ER with her 2-year-old boy due to the child's tonic convulsion. She states that he is usually sick; he has had recurrent infections since he was born. He also has special facial features: his eyes are separated by a wide space, and he is known to have a congenital heart disease. What is the most likely diagnosis?

DiGeorge syndrome

Your patient is a 3-year-old girl presenting with her mother, who is concerned that her child is mentally and physically "backward." She was born in the Caribbean after a normal pregnancy by unrelated parents. At birth, her weight was 9 pounds, and she had slight jaundice during the first week of life. Her first tooth appeared at 9 months. She held up her head at 5 months and sat with support at 7 months. Then, she grew apathetic, cried a lot, and never learned to grasp or hold objects. At the age of 9 months, she started having salaam attacks and head drops diagnosed as epileptic seizures, for which she was prescribed phenobarbital. Currently, she is having 1-4 grand mal seizures per month and several petit mal attacks daily. She had one attack of upper respiratory infection with fever, when her mother noticed that her urine and sweat had a musty odor. She also has mild eczema. There is no family history of mental abnormalities, and 2 older brothers (6 and 8 years old) are healthy. On examination, you find a well-nourished child with blonde hair and blue eyes who appears apathetic and uninterested in her surroundings. She has patchy eczema on her face. Occasionally, she smiles for no obvious reason. You also note the presence of repetitive organized movements. She does not fix attention, and it appears that she has difficulty in focusing her eyes. The rest of the examination, including hearing and vision, is within normal limits. Laboratory tests reveal mild sideropenic anemia, and serum aminogram shows slight elevation of phenylalanine but with normal biopterin. EEG demonstrates paroxysmal abnormalities. What therapy will you choose first to treat and prevent further cognitive decline in your patient?

Diet

5 and a half-year-old girl has been persistently bedwetting. She has never had a dry period. The mother also reports that the child is constipated, passing stools only once or twice every week. She is a fussy eater, eating mostly milk products. At the age of 1 and a half years, she had to have a fecal disimpaction by a local physician assistant for persisting constipation. She has heard a lot about bedwetting alarms and reward systems in teaching children to be continent. What measure should she pursue initially?

Diet modification, with laxatives if needed

3-year-old girl presents with terrible head pain, increasing fever, and irritability. On examination, you find the child febrile, 103°F, and she cries when you lift her head from the examining table. The neck appears to be quite stiff when manipulated. You perform a lumbar puncture. What findings would you expect if this child had bacterial meningitis?

Elevated protein

Your patient is 3-month-old male infant with failure to thrive. His family and prenatal history were uneventful. He was born by spontaneous vaginal delivery with an APGAR score of 10, and he has been breastfed since birth. The mother states that he has no appetite and cries when feeding. On examination, the baby does not seem to be in acute distress, his HR is 130/min, RR is 26 breaths/min, temperature 36.9 C, and BP is 125/70. Physical examination reveals hypotonia and the absence of subcutaneous fat; his skin is wrinkled, and his abdomen is prominent. He weighs 6 lbs (below the 3rd percentile for the age). His height is 22 inches (below the 3rd percentile for the age), and head circumference is 14.80 in (below the 3rd percentile for the age). The rest of the examination is normal. His laboratory tests show hypercalcemia (total calcium of 18.0 mg/dL, whereas the normal range is 9 - 10.5 mg/dL), low phosphate (4.4 - 4.5 mg/dL), low alkaline phosphatase (100 mg/dL, whereas the normal range is 143 - 320 mg/dL), and oxygen saturation of 75% at room levels. His chest X-ray shows irregular metaphyses, severe metaphyseal flaring, and osteopenia. Your initial diagnosis is hypophosphatasia. What laboratory finding will support your diagnosis?

Elevated urine phosphoethanolamine

9-year-old girl presents with a sore throat. The parents state that she began a fever a few days ago, reporting that her throat hurt. On physical exam, you note a red throat, a red and beefy tongue, tonsillar exudates, and swollen anterior cervical lymph nodes. The parents report a history of a severe anaphylactic reaction to penicillin. What antibiotic would treat this infection while minimizing the risk of invoking an allergic reaction?

Erythromycin

3-year-old girl has a fever. She complains that it burns when she urinates, and she has started wetting the bed again. The most likely bacterial organism in her urine would be:

Escherichia coli

12-year-old boy with HIV presents with a 1-month history of progressive confusion, lethargy, and memory loss. CT scan of the head reveals an isolated hypodense cerebral mass. Histologic examination reveals blast cells. There is no evidence of metastases. What is the most likely tumor type?

Non-Hodgkin's Lymphoma

A mother presents with a 5-week-old male infant for excessive vomiting. He has been having consistent episodes of projectile vomiting 30-40 minutes after feeding and is not gaining weight. The infant has no significant past medical history, although the mother mentions that she began renovating their Victorian-era house while pregnant. He has a 3-year-old sister, who is healthy and has no significant past medical history. What has the most likely diagnosis been most commonly associated with?

First-born male child

22-year-old woman has unilateral left renal agenesis incidentally discovered during ultrasound evaluation for cholecystitis. She has no ectopic kidneys and her blood pressure, urine protein, and serum creatinine are all normal. How should you manage her agenesis long term?

Follow blood pressure and urine protein/creatinine

A 15-year-old unmarried young woman delivered a healthy 7-pound baby girl. The parent had not received proper prenatal care because she was trying to hide her pregnancy from her parents. She did not inform her nurses of a persistent vaginal discharge she experienced prior to delivery. A week after delivery, the infant's eyes became filled with pus and swollen (see below). The infant also developed a short stuttering cough. Cultures of exfoliated cells from the infant's eyelids grew negative for bacteria. An endocervical swab of the mother was also negative. Microorganisms similar to those found in maternal endocervical scraping, examined by immunofluorescence, were also seen in the infant's conjunctival scrapings. The mechanism of transmission to the infant was MOST likely through:

Exposure during delivery

Chronic constipation leads a teenage patient to seek medical help. A barium enema revealed a megacolon involving the rectum and sigmoid colon. The differential for this problem included Hirschsprung's Disease. What is the embryologic process that is lacking for Hirschsprung's Disease?

Failure of neural crest cells to migrate to the wall of the colon

The delivery room calls to report a newborn has been delivered with a protruding upper midline abdominal mass. You find that it is a dark red, matted, stiff mass of abdominal viscera without a covering lining. What is the most likely diagnosis?

Gastroschisis

An African American male neonate born 12 hours ago presents with yellowish coloration of the whites of his eyes. His skin also appears darker and yellowish compared to his twin sister's skin. Pregnancy was normal, and the 23-year-old mother had no infections or complications and took no drugs during the pregnancy. Delivery was uneventful; the neonates were born on term with APGAR score 9 and 10, respectively. Family history of anemia, splenectomy, bile stones, and liver disease is negative, but the father has a "beans allergy" that presents with abdominal pain and jaundice. Peripheral smear does not reveal spherocytosis, echinocytosis, or eliptocytosis, but some keratocytes are present. Bilirubin levels in the patient are high (13 mg/dL) with direct bilirubin 1 mg/dL. Coombs test is negative and hemoglobin is low. What is the most likely diagnosis?

Glucose-6-phosphate dehydrogenase deficiency

10-year-old child complains of anorexia, malaise, mild fever, and sore throat for 2 days, then painful sore red spots some with blisters on the tongue, gum, inside of the cheek, palms, and feet. What is the most probable diagnosis?

Hand foot and mouth disease

5-year-old girl presents with a rash of clear and grayish vesicles on a reddened base. Her hands and feet are affected, including her palms and soles. She reports sores in her mouth. There is no desquamation to the rash. Her heart and lungs are clear. She is febrile, and there is an accompanying tachycardia. Her blood pressure is normal. Her oral cavity shows ulcerations. What is the most likely diagnosis?

Hand-foot-mouth disease

2-year-old girl is brought to an otolaryngologist by her mother for chronic ear infections. The patient is otherwise healthy, with the exception of recurrent episodes of otitis media (OM). Examination and history show that the child has had average growth and development; she has not had invasive infections, skin disorders, or hospitalization. The child's mother is concerned about the risk of hearing loss and its effects on development. What patient education information can you give the child's mother?

Hearing loss during OM may adversely affect cognition and language

12-year-old boy presents with a 3-day history of acute fever, left-sided chest pain, productive cough, nausea, and vomiting. His mother claims that he has been "dainty since birth"; he has had frequent upper respiratory infections, including several episodes of pneumonia. His stomach is frequently "upset", resulting in vomiting and diarrhea. His physical examination today is: HR 100 beats/min, BP 105/60 mmHg, temperature 38 °C, and RR 22 breaths/min. Respiratory examination reveals increased fremitus and hyper resonance, bronchial breath sounds, and crackles on the left. There is no lymphadenopathy; on the contrary, his tonsils are hypoplastic. The rest of the systemic examination is unremarkable. His laboratory data reveal elevated WBC with neutrophilia and elevated acute phase reactants. Extensive laboratory evaluation shows that serum electrolytes, BUN, creatinine, liver function tests, sweat test, CH50, AP 50, and candida skin test are all within normal limits. Arterial blood gases show pH of 7.40; PCO2 is 32 mmHg, PO2 is 68 mmHg, and O2 saturation is 94.5%. Chest X-ray shows patchy alveolar infiltrates in the left mid-to-low parts of the lung. Further laboratory investigations do not detect antibodies on tetanus and diphtheria toxoid. What is the most probable underlying defect in your patient?

Humoral immunity

What condition is demonstrated in the attached sonographic image?

Hydrocephalus

A 13-year-old boy came to the ER with a suddenly decreased vision in the right eye after being accidentally hit by ball in the face. On examination the right side of the face is full of bruises and the eye is shown in the following photograph. The vision is 20/40 and there are no cut wounds in the eye. The fundus examination shows no hemorrhage or edema. What is the most likely cause of the decreased vision?

Hyphema

2-year-old child presents with a tonic convulsion. His mother states that he is usually sick; he has had recurrent infections since he was born. His temp is 99° F. He also has special facial features; his eyes are separated by a wide space, and he is known to have a congenital heart disease. What is the most likely cause of the convulsion?

Hypoparathyroidism

A mother brought her 2-month-old infant son to a pediatric clinic because, during micturition, urine ran from the opening at the bottom of the midline groove of the scrotum instead of from the tip of the penis. What is the most likely diagnosis?

Hypospadias

14-year-old boy presents due to embarrassment after an incident in school: while undressing before the class in physical education, the other boys laughed at him because of his "underdevelopment." His personal and family history is non-contributory. What is a definitive sign of the onset of puberty in this patient?

Increase in size of testes

In response to a complaint by her kindergarten teacher, a mother brings her 4-year-old girl to her pediatrician. The child has been noticed spending time alone while at kindergarten, talking to her self and to imaginary friends. The conversations also occur at home. Her reading and writing are comparable to her classmates. At her bedside, she keeps a pillow and blanket for her companion. Her mother also reports that her child has frequent nightmares, sometimes waking her in the night in tears. The mother wants her child evaluated further. What is the most likely cause?

Normal development

A 12-year-old African American boy presents with poor appetite; he has felt unwell for over a month. He cannot delineate any specific symptoms, except feeling "puffy." He denies pain, eating disorder, rash, depression, drug use, and fevers. The family denies recent travel. PMH features no recent or chronic illnesses. He has had no surgeries and takes no medications. His family history includes grandparents on both sides with hypertension; one died from a kidney problem. ROS is negative except for some change in the urine, which he describes as frothy. He denies dysuria, gross hematuria, polyuria, and nocturia. Vitals: T 97.9°F; R 14, HR 90, BP 160/94. Weight is up 2 lb from his charted weight 3 months ago. HEENT, neck/thyroid, lungs, cardiac, abdominal, musculoskeletal, neurological, and derm exams are unremarkable. Examination of extremities reveals bilateral 1-2+ edema in the upper and lower extremities, with 2+ pulses.Basic laboratory studies: Test Result Complete blood count (CBC) Hematocrit 35.0% Rest of CBC Within normal limits Complete metabolic panel (CMP) Albumin 2.7 g/dL BUN 30 mg/dL Glucose 88 mg/dL Rest of CMP Within normal limits Dipstick Urinalysis Protein 3+ Blood 1+ Glucose Negative Ketones Negative Nitrites Negative Leukocyte esterase Negative Specific gravity 1.025 A urine protein-to-creatinine ratio shows 3.6 mg/mg. What is the primary explanation for the high level of proteinuria in this patient?

Increased glomerular permeability to protein

9-year-old boy presents with a 1-week history of fever, malaise, sore throat, headache, and body aches. Physical examination reveals that the child has a fever of 102°F. Throat shows congestion of the pharynx with tonsillar enlargement and some exudates. Cervical submandibular and epitrochlear lymph nodes are enlarged. The spleen is palpable 3 cm below costal margin, and the liver is 2.5 cm below costal margin. There is a maculopapular rash over the face, trunk, and the extremities. Blood examination shows leukocytosis with absolute lymphocytosis. Most lymphocytes are large, with pale blue vacuolated cytoplasm and an eccentric nucleus. The nucleus is irregular with a dense chromatin, and it is surrounded by a halo. What is the most likely diagnosis?

Infectious mononucleosis

14-year-old boy is brought to the Emergency Department by paramedics after being found in a neighbor's pool. He was pulled out of the pool by the neighbor who performed CPR until paramedics arrived. Regarding drowning events in children, which of the following statements is most accurate?

It is one of the top 3 causes of injury-related death in children worldwide

10-year-old girl presents because she has been moody lately. Her mother believes it is down to her lack of "development". The patient reveals that some girls in her class have had their 1st period and begun developing breasts. Despite being a year younger than most in her grade, she believes that there is something wrong. She has yet to attain menarche; she does not have breasts, and she has pre-pubescent axillary and pubic hair. On her growth chart, she is at the 3rd centile for height and at the 98th centile for weight. Her nipples appear to be widely spaced, and her elbow carrying angle appears wide. What is the most appropriate next step in management?

Karyotyping

Your patient is an 18-month-old boy whose parents are concerned that he is "mentally backward." He was born to a 27-year-old mother and delivered at term with no prenatal, labor, or postnatal complications. His birth weight was 3.6 kg, and he was breast fed for 3 months. Between 3 and 6 months, a babysitter took care of the boy while the mother began renovating an old farm house the family wanted to move into. The mother has had several episodes of stomach aches and severe nausea that she thinks have been caused by unhealthy foods since beginning renovations. Also, heavy physical activity (sanding and torching) left her feeling very tired and weak. As soon as the renovation was completed, the family moved into their new home and the child has since lost his appetite, has frequents attacks of abdominal pain and constipation, vomits often, and is not gaining weight as expected. He rolled over at 5 months, sat without support at 7 months, crawled at 10 months, and began to walk around 14 months, but most worrisome is the fact that he is still not talking; he started to babble at about 9 months of age and only recently learned a few words such as "Dada" and "Boo." At the examination, you find a pale irritable child without dysmorphic features. His height and weight are both less than the 5th percentile. Currently, his speech is at the 7- to 9-month level, motor skills at a 6-month level, and the rest of examination is not contributing. Routine laboratory test shows microcytic anemia with normal iron studies. What is the most probable cause of developmental delay in this child?

Lead

A 2-year-old boy presents with his mother due to her concerns about his paleness; she states that he used to be playful, but now looks tired and doesn't even cry as he did previously. She first noticed this occuring 3 months after moving to his grandmother's old house. CBC is ordered and shows the following results: RBC 4 million/microliter, WBC 11,000/mm3, Hb 9 mg/dL, platelets 180,000/mm3, and hematocrit 31%. The image shown is of his blood film. What is the most likely diagnosis?

Lead poisoning

18-month-old boy presents with delayed sitting and an inability to stand up. His mother has noticed that he consistently bites his lips and fingers to the extent that it leads to injury. He also shows delayed language development. On review of the family history, the mother states that she and her husband are healthy and well; one of her brothers has a disorder that causes renal stones, and he is wheelchair-bound and always kept restrained. What is the most likely diagnosis?

Lesch-Nyhan Syndrome

A young woman presents with her daughter, who appears to be about 6 years old. You note that the child's eyes are downcast and she is scratching her scalp. On closer inspection, you note a tiny white wingless insect and tiny eggs attached to the hair shafts. The child's mother also notes that the same insects are present in the girl's eyelashes. What is the most likely diagnosis?

Lice

The 2-year-old girl (shown below) has normal stature for her age and clear corneas, but mildly coarsened facial features and slowly progressive behavioral symptoms, including sleep disturbances, temper tantrums, and atypical aggressive behavior. She excretes abnormally high quantities of heparin sulfate in her urine, and she clearly suffers from a mucopolysaccharidosis (MPS). What is the most likely diagnosis?

MPS III (Sanfilippo disease)

6-year-old boy presents for the evaluation of frequent upper respiratory infections, vomiting, and diarrhea that started when he was around 6 - 7 months old. He was born after an uneventful pregnancy; he was not breastfed, and his immunizations are up to date. His older brother was diagnosed with Bruton's hypogammaglobulinemia. Except for the tonsillar hypoplasia, his physical examination today is normal. Extensive laboratory evaluation shows that serum electrolytes, BUN, creatinine, liver function tests, sweat test, CH50, AP 50, and candida skin test are all within normal limits; no antibodies on tetanus and diphtheria toxoid are detected. What prevented the development of infections in this child during the first 6 months of life?

Maternal IgG

A newborn infant is delivered at 30 weeks since the last menstrual period. At birth, the infant weighs 1,500 grams, but otherwise appears normal. Soon after birth the infant becomes cyanotic and breathes with a grunting noise. Chest X-rays reveal dense lungs with significant atelectasis. What is the most significant predictive prenatal test for the newborn infant's condition?

Measurement of amniotic fluid lecithin/sphingomyelin ratio

3-year-old girl presents to her pediatrician with perianal itching that wakes her up at night. Her pediatrician performs an anal swab, and microscopic examination reveals eggs. What is the most likely recommended treatment for this patient?

Mebendazole

Routine obstetric sonography reveals anomalies of the fetus which may or may not be of concern. During the examination an echogenic area that appears attached to the venous portion of the cord is imaged. Doppler analysis of the cord reveals normal flow in both arteries and the vein. The mother reveals that she fell down stairs a few weeks ago, but did not tell her clinician. The patient denies any bleeding, pain, or decreased fetal movement. Which of the following is a differential for this finding?

Mechanical trauma causing a hematoma

23-month-old boy presents with a sudden onset of bright red blood in his bowel movements. He is afebrile and does not seem to be in any pain. A technetium-99m pertechnetate scan after enhancement with cimetidine shows a 'hot spot' in the area of his ileum. What is the most likely cause?

Meckel diverticulum

After 22 hours of difficult labor, a 25-year-old primigravida delivers a full-term female neonate. Both baby and the placenta demonstrated green staining. The USG at 20 weeks showed normal development for age; major organs were identified and normal in size for the age. Amniotic fluid volume was normal. An alpha-fetoprotein level was in the normal range. What condition is most likely to explain the respiratory distress that develops in this neonate?

Meconium aspiration

A 1-year-old boy (shown below) has low serum copper and ceruloplasmin, intellectual disability, sparse, kinky pale hair, hypotonia, and myoclonic seizures. The child's karyotype is an apparently normal 46, XY. The MOST likely diagnosis is:

Menke syndrome

15-year-old boy with no significant past medical history is seen in the Emergency Department after he had collapsed after a dental extraction in which prilocaine hydrochloride was used as topical anesthesia. He states that during the procedure he did not feel well. Shortly after the procedure, he developed a headache, difficulty breathing, and a bluish skin colon. Physical examination reveals an ill-appearing young man in moderate distress. He is cyanotic and tachypnic. His breath sounds are clear equally. Although in distress, he is alert and oriented. A sample of his arterial blood is drawn and noted to have a deep brown color that does not turn red when exposed to air. The patient is treated with IV methylene blue and begins to improve within 1 hour of treatment. What is the most likely cause of this patient's symptoms?

Methemoglobinemia

A 6-week-old infant was the product of an uncomplicated pregnancy, labor, and delivery. She has been breast-feeding well with only the occasional spit-up. Stools have been seedy, yellow, and at the rate of 5-6 times per 24 hours. Over the last 24 hours, she has vomited 6-7 times. The last 2 have produced yellow-green material. She has not stooled in the last 24 hours. She is markedly lethargic and has a tense distended abdomen. The differential diagnosis includes:

Midgut volvulus

12-year-old girl presents because her joints are hurting. Her knees and ankles have been painful, warm, and swollen for several weeks now. Symptoms first started in her left knee, then her left ankle became involved, and then her right knee was affected. Her left knee is "almost back to normal now," but the other involved joints are becoming more painful. She is a middle school student and has been unable to go to school for the past 3 days because of the pain. She is taking acetaminophen arthritis formula, but the pain continues to get worse. Her mother did not want to give her non-steroidal anti-inflammatory medications because of her age. Review of systems (ROS) is positive for fever, chills, malaise, mild chest pain when lying down, moderate headaches, and weight loss. ROS is negative for sexually transmitted diseases, trauma to affected joints, tick exposure, and recent travel. What component of the physical exam would lead you to suspect acute rheumatic fever as the cause of her joint pain?

Mitral regurgitation

A 12-year-old African American boy presents with a 1-month history of poor appetite and has complained of overall not feeling well. When questioned, the boy cannot delineate any specific symptoms except that he feels "puffy." He denies pain, eating disorder, rash, depression, drug use, and fevers. The family denies recent travel. His PMH is unremarkable with no recent or chronic illnesses. He has had no surgeries, and he takes no medications. His family history includes grandparents on both sides with hypertension, with one of these grandparents also having died from some type of kidney problem. His ROS is entirely negative except for the above symptoms and some noted change in urine, which he describes as frothy. He denies dysuria, gross hematuria, polyuria, and nocturia in the ROS. On physical exam, his vitals are: Tem: 97.9°F; Resp 14; HR 90; BP 120/74 mm Hg right arm sitting. It is noted weight is up 2 pounds from his charted weight 3 months ago. HEENT, neck/thyroid, lungs, cardiac, abdominal, musculoskeletal, neurological and derm exams are unremarkable. Examination of extremities reveals bilateral 1-2+ edema in the upper and lower extremities, with 2+ pulses. Basic laboratory studies were ordered and results are available at the time of visit. Test Result Complete blood count (CBC) Hematocrit 35.0% Rest of CBC Within normal limits Complete metabolic panel (CMP) Albumin 2.7 g/dL BUN 30 mg/dL Glucose 88 mg/dL Rest of CMP Within normal limits Dipstick Urinalysis Protein 3+ Blood 1+ Glucose Negative Ketones Negative Nitrites Negative Leukocyte esterase Negative Specific gravity 1.025 Given the proteinuria, a urine protein-to-creatinine ratio is obtained, showing 3.6 mg/mg. What is the most likely diagnosis?

Nephrotic syndrome

9-year-old boy has 11 irregularly shaped, 2 X 3 cm, hyperpigmented lesions on the skin of his trunk. He has freckles in his axilla. He recently developed several cutaneous and subcutaneous masses and some visual disturbances. What is the most likely diagnosis?

Neurofibromatosis

5-month-old infant was found cold and blue by his mother when she went to feed the baby. The infant was born prematurely at 34 weeks of gestation with a low birth weight of 4 pounds. He was the third child of a 20-year-old female. The child was developing normally with no major illnesses. The autopsy in this case will probably reveal

No abnormal finding

24-year-old woman, gravida 4, para 2, abort 1, presents to the sonography department for a mid-pregnancy examination. She is sure her last menstrual period was 24 weeks ago, but is considered LGA and has an elevated MSAFP. The sonographic examination reveals a female fetus with a femur length appropriate for 24 weeks; however, the fetal head measures below 2 standard deviations. Facial examination reveals the presence of a cleft maxilla and the feet are bilaterally clubbed. The abdominal circumference is also small, and echogenic dilated loops of bowel are seen in the amniotic fluid. Surface appearance of the bowel is smooth, indicating a membrane. What condition is a differential diagnosis?

Omphalocele

18-month-old boy presents with a 9-month history of progressively increasing pallor and failure to gain weight. Weight is 7.5 kg, length is 73 cm, head circumference is 44 cm. Physical examination reveals liver palpable 4 cm below costal margin and spleen palpable 3.5 cm below costal margin. Skeletal survey reveals diffuse bone sclerosis with loss of differentiation between cortex and medullary cavity. Lab results: Hemoglobin 6 g/dL Total leukocyte count 3900/mm3 Platelet count 52,000/mm3 Normal MCV and MCH What is the most likely diagnosis?

Osteopetrosis

A child presents with a cat bite that occurred yesterday; the parents are concerned about infection. The parents state that the child was playing with a neighborhood cat that appears to be homeless. The child pulled on the cat's tail and the cat bit the child on the hand. On exam, the 2 puncture wounds appear red and swollen. What aerobe does the patient most likely have?

Pasteurella species

A mother brings in her 6-year-old daughter because the girl's teacher is concerned about behaviors at school. The teacher has noticed the girl "staring off into space" frequently throughout the day; the teacher is able to get the girl's attention only occasionally. There are also periods when she appears to be talking to herself, but there is no sound coming from her mouth. The mother states that there are times when her daughter does not seem to be paying attention to what the mother is saying. Shortly after these episodes, the child engages in conversation without any problem, so the mother did not think the episodes were an issue. There is no concern about other abnormal behavior or discipline issues at home or at school. What is the most likely diagnosis?

Petit mal (absence) seizures

You are examining a 6-month-old male infant who has not received any immunizations since birth. He was born at home and has a history of multiple respiratory tract infections and chronic diarrhea since birth. His parents are not related. Family history is significant for two of his older brothers dying of pneumonia at ages 8 and 1. His 4-year-old sister is healthy. His parents moved to the US from an underdeveloped country 3 months ago. They are worried because one of their neighbors' children (age 6) developed a pruritic skin rash and fever 2 days ago; another child (age 6 months) is in the hospital because of severe vomiting and diarrhea. On examination, your patient's vitals are normal. His weight is <5th percentile, his height is at the 5th percentile, and his head circumference is at the 50th percentile. Physical exam shows an eczematous skin rash, and mucocutaneous changes suggestive to a fungal infection are noted. His thyroid, heart, lungs, abdomen, genitalia, and nervous system are within normal limits. There are no palpable lymph nodes and no hepatosplenomegaly. What vaccine should you recommend?

Pneumococcal vaccine (PCV13)

In the winter, an 11-month-old male infant presents with a 2-day history of vomiting, diarrhea, and fever. He has not had routine medical care since birth. Mother reports no significant past medical history. His temperature is 102°F. Clinically, he appears dehydrated; his white blood cell count is 5400 cells/mm3 with a normal differential. His stool and urine are negative for white blood cells. What is the most likely cause of gastroenteritis in this child?

Rotavirus

A newborn infant presents with central cyanosis on day 1 of life. An increased left ventricular impulse is noted. There is a holosystolic murmur heard along the left sternal border. Second heart sound is single. X-ray chest shows oligemic lung fields. ECG shows left axis deviation and left ventricular hypertrophy. What is the drug of choice for the management of this infant?

Prostaglandin E1

24-year-old Caucasian woman, gravida 2 para 2, presents in a distressed state. She brought her 5-day-old daughter with her and reports that the child started to bleed spontaneously from her vagina. The pregnancy was without any complications; labor was at term and occurred spontaneously without any problems. Examination of the child reveals an afebrile child with blood at the introitus. The child does not appear to be in pain, and she sleeps through the examination. What is the next step in management?

Reassurance

Parents bring their 4-year-old daughter in because of knock-knee. She is otherwise healthy, and her height is in the 50th percentile for age. On examination, she has about 10 degrees of valgus. What should you recommend?

Reassurance that this is normal for age

A newborn infant is delivered at 30 weeks since the last menstrual period. At birth, the infant weighs 1500 gm but otherwise appears normal. Soon after birth, the infant becomes cyanotic and breathes with a grunting noise. Chest X-rays reveal dense lungs with significant atelectasis but no cardiovascular abnormalities. What is the most likely diagnosis?

Respiratory distress syndrome

The mother of a 2-year-old boy came to the outpatient clinic concerned about deviation of the right eye of her child. She has also noticed that the pupil is white. She said she noticed these features a few weeks ago and that it is stationary. He was born at 40 weeks of gestation, had up-to-date vaccination, and never complained of anything regarding his eyes, which were normal. What condition is the primary suspect to exclude in diagnostic workup?

Retinoblastoma

5-year-old boy presents with an ankle injury. While on his school's playground, he was playing on the swings and decided to jump off. An X-ray of the ankle demonstrates a fracture line through the metaphysic plate of the superior aspect of the distal fibula, ending before the epiphyseal plate. What type of Salter-Harris fracture does this child have?

Salter-Harris type II

3-day-old male infant is seen in the NICU. He was a breech delivery, but the birth was otherwise uneventful. He had a normal Apgar score and is feeding well. Physical examination is remarkable for excessive plantar flexion of both feet with the soles facing inward. What is the best management option for this condition?

Serial cast application

16-month-old African American boy presents with a 2-day history of irritability and refusal to bear weight. His mother denies any recent history of fever, vomiting, diarrhea, rash, or trauma. Family history is significant for a maternal uncle who had a stroke and died when he was 35. On exam, vital signs are stable. Patient appears smaller than stated age and is irritable but consolable. He is in no apparent distress, but he refuses to bear weight or play. The only significant findings on exam are swollen hands and feet. CBC reveals WBC 18,000 mm3, with 40% neutrophils, 30% lymphocytes, and 1% monocytes. Hb is 8 g/dL and platelets are 400,000 mm3. What test would be helpful in making a diagnosis?

Sickle cell solubility test

2-year-old Caucasian boy presents with a 1-month history of decreased energy and increased somnolence. His mother admits that he is a picky eater and that he "loves to eat mattresses." Review of systems reveals that he drinks milk only with cereal and has occasional constipation. His vital signs are within normal limits. You suspect this patient may have iron deficiency anemia. What finding is most supportive of this diagnosis?

Spoon nails: 6 Hb (g/dL), 68 MCV (fL), and decreased reticulocyte count

4-year-old boy is brought to the office by his mother. She is worried that he still wets his bed at night. He had a normal delivery with a birth weight of 3.4 kg and has had normal developmental milestones up to this point. She is extremely anxious and seeks reassurance about this problem. She said that lately she has been punishing him for each nocturnal occurrence and that this does not seem to help. All of his lab values appear to be normal. What is the next step for the doctor to take?

Stop punishment and follow up

8-year-old boy presents in January with a fever, pharyngeal erythema, tonsillar exudates, and enlarged cervical lymph nodes. He does not have a cough; his tympanic membrane is normal and does not show any signs of conjunctivitis. What is the most likely diagnosis?

Strep throat

15-year-old boy was healthy until 3 months ago. He has been having episodes of crampy abdominal pain and explosive liquid stools 2-3 times a day. He has had intermittent fevers and has noted blood in the stool. He has a documented 15-lb weight loss. Biopsied obtained at colonoscopy revealed inflammation with distorted crypt architecture and erosion of the mucosal later. What is the best way to start treatment?

Sulfasalazine

2-year-old boy is evaluated by a specialist at his primary physician's referral. His medical records indicate multiple admissions; there were 2 for CMV pneumonia, pneumocystis pneumonia, esophageal candidiasis, and severe herpes simplex labialis. His mother says her pregnancy and delivery were uneventful. Soon after birth, the child had multiple seizures due to an electrolyte disturbance; the mother is not sure exactly what the disturbance was. Immunoglobulin levels are normal. There is no significant family history of disease. Examination reveals a malnourished baby with flat facies and a fish-shaped mouth. The rest of the examination appears normal. A chest X-ray shows the absence of a 'sail sign'. What is the likely pathogenic mechanism?

T cell dysfunction

An 18-month-old boy presents for evaluation of frequent infections. His past medical history is significant for several episodes of otitis media and 2 upper respiratory tract infections. The infections responded to the antibiotics on each occasion. He has 2 sisters that are healthy and are not prone to infections. His immunizations are up to date. Physical examination reveals a pale boy whose height and weight are below the 3rd percentile; his tonsils are hypoplastic. The rest of the examination is normal. His blood type is A+, and his laboratory results shows panhypogammaglobulinemia, very low CD19 and CD20, and normal CD3. What will be a further confirmation of the diagnosis?

The absence of isohaematogglutinins

You are examining a 6-month-old male infant who is receiving sulfamethoxazole/trimethoprim IV 20 mg/kg for suspected Pneumocystis jiroveci pneumonia. The patient has suffered respiratory tract infections and chronic diarrhea since birth. His parents are not related. 3 of his older brothers died of pneumonia at the age of 6, 8, and 12 months; however, both his 10-year-old sister and 12-year-old sister are healthy. On examination, his vitals are normal; his weight, height, and head circumference are lower than expected for the age. Eczematous skin rash and thrush are noted. You are not able to palpate the lymph nodes; there are no signs of hepatosplenomegaly, and the rest of the examination is normal. What do you expect that the chest X-ray of this patient will reveal?

The absence of thymus shadow

4-year-old boy is taken to the Emergency Department after ingesting household plant fertilizer that he found in his garage. While in the ED, he was found to be lethargic, light-headed, cyanotic, and tachypnic. A sample of his arterial blood was taken and was found to be chocolate brown in color. Laboratory analysis revealed higher than normal levels of methemoglobin in his blood. What is true regarding this patient's condition?

There are acquired and inherited forms of the disease.

15-year-old boy sees a dermatologist because of concern over a "mole" he has had since birth. The dermatologist reassures him that it is just a supernumerary nipple. Where are supernumerary nipples typically found?

Thorax

4-year-old boy presents with bloody diarrhea, anemia, thrombocytopenia, fever, and lethargy following the exposure to the homemade hamburgers. His urine output is decreasing. What is the acute mechanism of kidney failure in this child?

Thrombotic microangiopathy

15-year-old boy was healthy until 3 months ago. He has been having episodes of crampy abdominal pain and explosive liquid stools 2-3 times a day. He has had intermittent fevers and has noted blood in the stool. He has a documented 15-lb weight loss. What is the most likely diagnosis?

Ulcerative colitis

2-month-old female infant was born after an uncomplicated pregnancy, labor, and delivery. The baby was fed artificial formula rather than nursed by her mother. She had an uncomplicated neonatal course and was well until about 1 month of age. Since that time, she has had some vomiting every day and has very loose, wet, runny yellow to green stools. In the last several days, her parents have noted red flecks in her stools. She has had intermittent periods of fussiness. What would be the MOST likely item in the following differential diagnosis?

cow's milk allergy

5-year-old child on broad-spectrum antibiotics for a lower respiratory tract infection develops explosive watery diarrhea with fever, abdominal cramps, and vomiting. Stool examination is positive for occult blood. Clostridium difficile is detected in the stool. What is the best treatment for this patient?

Vancomycin

17-year-old girl presents to the clinic due to chronic fatigue. Her past medical history is unremarkable. There is no history of surgeries. Review of systems reveals heavy monthly menses since menarche at age 13. She admits to using more than 20 tampons on each of the heaviest 3 days of her menstrual cycle. Her last menstrual cycle commenced 1 week ago. There are no recent medications. Exam is within normal limits, with no vaginal discharge. Labs: pregnancy test negative; cervical cultures negative; thyroid studies within normal limits; Hb 10 g/dL, WBC 9000/μL, platelet count 250 x 103/μL. Peripheral blood smear is consistent with microcytic hypochromic anemia. Prothrombin time, partial thromboplastin time (PT, PTT), and fibrinogen are normal. Bleeding time is prolonged. What is the most likely diagnosis?

Von Willebrand disease

An 18-month-old boy presents with delayed sitting and an inability to stand up. His mother has noticed that he consistently bites his lips and fingers to the extent that it leads to injury. He also shows delayed language development. On review of the family history, the mother states that she and her husband are healthy and well; one of her brothers has a disorder that causes renal stones, and he is wheelchair-bound and always kept restrained. What is the most likely mode of inheritance?

X-linked recessive

A 30-year-old primigravida in her third trimester presents with decreasing urine output, fatigue, and tremors over the past 3 days. She was previously healthy and had an uneventful pregnancy. Physical exam shows a blood pressure of 110/80 mm Hg, mild bibasilar pulmonary edema, and mild bilateral lower leg edema. She is normorreflexic. Uterine ultrasound: partial concealed placenta abruption and fetus with a slow heart rate Renal ultrasound: mild, right greater than left, hydronephrosis and normal sized kidneys with decreased, right greater than left, renal cortical echogenicity. Laboratory work shows Urinalysis: 300 cc/day. Dark yellow urine. No casts. No cells. ++blood +protein Serum creatinine: 2mg/dl Serum potassium: 5.0 meq/l Serum bicarbonate: 20 meq/l Total white blood cell count: 6.0x103/mm3 What is her most likely diagnosis?

a. Renal cortical necrosis

2-month-old female infant was born after an uncomplicated pregnancy, labor, and delivery. The baby was fed artificial formula rather than nursed by her mother. She had an uncomplicated neonatal course and was well until about 1 month of age. Since that time, she has had some vomiting every day and has very loose, wet, runny yellow to green stools. In the last several days, her parents have noted red flecks in her stools. She has had intermittent periods of fussiness. The component of cow's milk that causes the allergic reaction is thought to be:

beta-lactoglobulin