Myasthenia Gravis

Myasthenia Gravis Diagnostic Studies

Diagnostic Studies The diagnosis of MG can be made based on history and physical examination. However, other tests may be used to confirm a diagnosis. EMG may show a decreased response to repeated stimulation of the hand muscles, indicative of muscle fatigue. Single-fiber EMG is sensitive in confirming the diagnosis of MG. Use of drugs may also aid in the diagnosis. In addition, serologic testing for specific antibodies is useful. The Tensilon test in a patient with MG reveals improved muscle contractility after IV injection of edrophonium chloride (Tensilon), which is an anticholinesterase agent. (Anticholinesterase blocks the enzyme acetylcholinesterase.) This test also aids in the diagnosis of cholinergic crisis (secondary to overdose of anticholinesterase drug), which occurs due to excessive cholinesterase inhibition. Clinical features include muscle fasciculation, sweating, excessive salivation, and constricted pupils. In this condition, edrophonium does not improve muscle weakness but may actually increase it. Atropine, a cholinergic antagonist, should be readily available to counteract the effects of edrophonium when it is used diagnostically. In patients with a confirmed diagnosis of MG, a chest CT scan may be done to evaluate the thymus.

Myasthenia Gravis Patho

Autoimmune process, antibodies attack acetylcholine (ACh) receptors. This results in a decreased number of ACh receptor (AChR) sites at the neuromuscular junction. This prevents ACh molecules from attaching to receptors and stimulating muscle contraction. Anti-AChR antibodies are detectable in the serum of 90% of patients with generalized MG. In the 10% of patients who lack autoantibodies to AChR, their muscular weakness may be related to autoantibodies to muscle-specific tyrosine kinase or to other unknown antigens. Thymic hyperplasia and tumors are common in patients with MG, suggesting autoantibody production occurs in the thymus.

Myasthenic Crisis

Causes Exacerbation of myasthenia following precipitating factors or failure to take drug as prescribed or drug dose too low Differential Diagnosis Improved strength after IV administration of anticholinesterase drugs Weakness within 1 hr after ingestion of anticholinesterase drugs Increased weakness of skeletal muscles manifesting as ptosis, bulbar signs (e.g., difficulty swallowing, difficulty articulating words), or dyspnea

Cholinergic Crisis

Causes Overdose of anticholinesterase drugs resulting in increased ACh at the receptor sites, remission (spontaneous or after thymectomy) Differential Diagnosis Weakness within 1 hr after ingestion of anticholinesterase drugs Increased weakness of skeletal muscles manifesting as ptosis, bulbar signs, dyspnea Effects on smooth muscle include pupillary miosis, salivation, diarrhea, nausea or vomiting, abdominal cramps, increased bronchial secretions, sweating, or lacrimation

Myasthenia Gravis Clinical Manifestations

Clinical Manifestations and Complications The primary feature of MG is fluctuating weakness of skeletal muscles. The condition usually affects multiple muscle groups, including muscles used to move the eyes and eyelids, chew, swallow, speak, and breathe. These muscles are generally strongest in the morning and become exhausted with continued activity. By the end of the day muscle weakness is prominent. A period of rest usually restores strength. At onset, only the ocular muscles are involved for about 50% of patients; bilateral ptosis and constant or transient diplopia result. The disease does not progress beyond the ocular muscles in about 20% of patients. When facial muscles are affected, facial mobility and expression can be impaired. Patients may have difficulty chewing/swallowing food. Speech is affected, and the voice often fades after a long conversation. The muscles of the trunk and limbs are less often affected. Of these, the proximal muscles of the neck, shoulder, and hip are more often affected than the distal muscles. No other signs of neural disorder accompany MG. No sensory loss occurs, reflexes are normal, and muscle atrophy is rare.

Myasthenia Gravis/ Drug Therapy

Drug Therapy. Drug therapy for MG includes anticholinesterase drugs, alternate-day corticosteroids, and immunosuppressants. Anticholinesterase drugs are given to enhance transmission at the neuromuscular junction. Acetylcholinesterase is the enzyme that breaks down ACh. Thus inhibition of this enzyme by an anticholinesterase inhibitor will prolong the action of ACh and facilitate transmission of impulses at the neuromuscular junction. Pyridostigmine (Mestinon) is the most successful drug of this group in the long-term treatment of MG. Tailoring the dose to avoid a myasthenic or cholinergic crisis often presents a clinical challenge. Corticosteroids (specifically prednisone) are used to suppress the immune response. Drugs such as azathioprine (Imuran), mycophenolate (CellCept), and cyclosporine (Sandimmune) may also be used for immunosuppression. Many drugs are contraindicated or must be used with caution in patients with MG. Classes of drugs that should be cautiously evaluated before use include anesthetics, antidysrhythmics, antibiotics, quinine, antipsychotics, barbiturates and sedative-hypnotics, cathartics, diuretics, opioids, muscle relaxants, thyroid preparations, and tranquilizers.

Myastenia Gravis (MG)/Interprofessional Care

Interprofessional Care Diagnostic Assessment • History and physical examination • Fatigability with prolonged upward gaze (2-3 min) • Muscle weakness • EMG • Tensilon test • Acetylcholine receptor antibodies • Chest x-ray

Myastenia Gravis (MG)/Interprofessional Care

Management • Drug therapy • Anticholinesterase agents • Corticosteroids • Immunosuppressive agents • Surgery (thymectomy) • Plasmapheresis • IV immunoglobulin G EMG, Electromyography.

Myasthenia Gravis Info

Myasthenia gravis (MG) is an autoimmune disease of the neuromuscular junction characterized by the fluctuating weakness of certain skeletal muscle groups. This weakness increases with muscle use. MG occurs in either gender and in people of any ethnicity. The prevalence rate is approximately 20 per 100,000; currently an estimated 60,000 people have MG in the United States. The mean age at onset in women is 28 years; in men the mean age at onset of MG is 42 years. Women are affected more often than men (3 : 2). In older adults, both men and women are equally affected.

Myasthenia Gravis/Myasthenic Crisis

Myasthenic crisis is an acute exacerbation of muscle weakness triggered by respiratory infection, surgery, emotional distress, pregnancy, exposure to drugs that may increase myasthenic weakness, or beginning treatment with corticosteroids. The major complications of MG result from muscle weakness in areas that affect swallowing and breathing. This results in aspiration, respiratory insufficiency, and respiratory tract infection.

myasthenia gravis (MG)/Nursing Assessment

Nursing Assessment Assess the severity of MG by asking the patient about fatigability, what body parts are affected, and how severely they are affected. Some patients become so fatigued that they are no longer able to work or even walk. Assess the patient's coping abilities and strategies as well as understanding of the disorder. Objective data should include respiratory rate and depth, O2 saturation, arterial blood gas analyses, pulmonary function tests, and any evidence of respiratory distress in patients with acute myasthenic crisis. Assess muscle strength of all face and limb muscles, swallowing, speech (volume and clarity), and cough and gag reflexes.

Myastenia Gravis (MG)/Sugrical/Other therapies

Surgical Therapy. Because the presence of the thymus gland in the patient with MG appears to enhance the production of AChR antibodies, removal of the thymus gland results in improvement in a majority of patients. Thymectomy is indicated for almost all patients with thymoma, for patients with generalized MG between the ages of puberty and about 65 years, and for patients with purely ocular MG. Other Therapies. Plasmapheresis and IV immunoglobulin G can yield short-term improvement in symptoms. They are indicated for patients in myasthenic crisis or in preparation for surgery when corticosteroids must be avoided. Plasmapheresis directly removes circulating AChR antibodies, leading to a decrease in symptoms. It is not certain how IV immunoglobulin works, but it is probably related to a decrease in antibody production.

Myasthenia Gravis Clinical Manifestations

The course of this disease is highly variable. Can have short-term remissions, others may stabilize, and others may have severe, progressive involvement. Exacerbations of MG can be precipitated by emotional stress, pregnancy, menses, another illness, trauma, temperature extremes, and hypokalemia. Ingestion of drugs, including aminoglycoside antibiotics, β-adrenergic blockers, procainamide, quinidine, and phenytoin, can aggravate MG. Psychotropic drugs (e.g., lithium carbonate, phenothiazines, benzodiazepines, tricyclic antidepressants) have also been associated with worsening of myasthenia, as have neuromuscular blocking agents (tubocurarine chloride, pancuronium, succinylcholine [Anectine]).

Myastenia Gravis (MG)/Nursing IMP

The patient with MG who is admitted to the hospital usually has a respiratory tract infection or is in an acute myasthenic crisis. Nursing care is aimed at maintaining adequate ventilation, continuing drug therapy, and watching for side effects of therapy. Be able to distinguish cholinergic from myasthenic crisis (Table 58-19) because the causes and treatment of the two conditions differ greatly. As with other chronic illnesses, focus care on the neurologic deficits and their impact on daily living. Teach the patient about a balanced diet that can easily be chewed and swallowed. Semisolid foods may be easier to eat than solids or liquids. Scheduling doses of drugs so that peak action is reached at mealtime may make eating less difficult. Arrange diversional activities that require little physical effort and match the patient's interests. Help the patient plan activities of daily living to avoid fatigue. Teaching should focus on adherence to the medical regimen, complications of the disease, potential adverse reactions to specific drugs, and complications of therapy (crisis conditions), and what to do about them. Explore community resources such as the Myasthenia Gravis Foundation of America and MG support groups.