Myasthenia Gravis

What is the prognosis for MG?

Crisis - generally good (mortality less than 5%) if recognized and managed MG overall consists of a near normal life expectancy

What is plasma exchange used for MG treatment?

Short term intervention for patients with sudden worsening Preop strengthening Nearly all patients will improve temporarily but variable when in course of treatment Effect best when followed by thymectomy or immunosuppressive therapy

What are the clinical manifestations of a severe exacerbation of MG?

Slack facial muscles, expressionless face Weak neck muscles (unable to support head) Slack jaw Nasal qualtiy to voice Gag reflex absent Respiratory distress Aspiration PNA

MG initial onset clinical presentation.

Specific muscle weakness (not generalized weakness) Severity fluctuates during the day (least in morning, worst in evening) Course is variable but progressive

What populations are usually affected by MG?

Younger onset most common in Asian population Male:Female ratio 2:3 Female predominance in young adult onset Male predominance in older adult onset Peaks in onset in neonates, age 20-30 and older than 50 years of age

Myasthenia Gravis Definition

Rare autoimmune disorder Antibodies form against acetylcholine nicotinic neurotransmitter receptor at the myoneural junction. Results in decreased number of Ach receptors Results in reduced muscle strength with repeated use Recovery of muscle strength after rest A chronic disease with exacerbations

What is the treatment for MG crisis?

Rule out medication overdose via history Restart cholinesterase inhibitors Corticosteroids Plasma exchange/IVIG Management of respiratory failure Address underlying mechanism (infection, fever management)

How do Cholinesterase inhibitors work?

Decrease the breakdown of ACh at the neural junction allowing more ACh to be available. Response is variable and patient specific Most common reported adverse effects are GI (nausea, diarrhea, abdominal cramping, increased oral or bronchial secretions)

How is MG diagnosed?

Edrophonium Chloride (Tensilon) Test or neostygmine test Test for MG antibodies EMG - repetitive nerve stimulation or single muscle stimulation Combined testing often required

What will exacerbations of MG be caused by?

Emotional upset Systemic illness (esp resp infections) Hypothyroidism or hyperthyroidism Pregnancy Menstrual Cycle Drugs affecting neuromuscular transmission Increase in body temperature

What is the main limitation in corticosteroid treatment of MG?

Major limitation is chronic effects of high dose corticosteroids May exacerbate in the first 2 weeks, then progress to remission

What is the natural progression of MG in the initial presentation?

Maximum weakness occurs during the first year in 2/3 of patients 15-20 years after diagnosis weakness often becomes fixed and the most severely involved muscles are frequently atrophic

Patho of MG

Normal muscle contraction is initiated by ACh exchange over neuronal junction. Antibodies develop against ACh nicotinic postsynaptic receptors Thymus abnormal in 75% of patients

What is the treatment for MG?

Not much randomized controlled trial data to guide MG treatment Treatment often guided most by patient response Cholinsterase inhibitors Thymectomy Corticosteroids Immunosuppressant drugs Plasma Exchange IVIG

What muscles are typically affected by MG?

Ocular muscles, ptosis, diplopia Oropharyngeal weakness Limb weakness

Explain Thymectomy.

Often recommended for all MG patients Probably best in younger patients who are earlier in the course of their disease, improvement rarely seen in people with onset over age 60 Patients without thyoma seem to respond better

What is the Tensilon test most accurate for testing?

Patients with bulbar symptoms

What is the clinical presentation of cholinergic crisis?

Too much medication may present similarly to MG crisis Excess cholinesterase inhibitors (neostigmine, pyridostigmine, physostigmine) Excess ACh produces flaccid muscle paralysis as well May cause bronchospasms, wheezes, respiratory failure Miosis and SLUDGE syndrome may be seen DTRs present Indistriguishable from MG crisis