Myasthenia gravis
Myasthenia gravis is an autoimmune disorder of the postsynaptic neuromuscular junction, most often caused by acetylcholine receptor antibodies, producing fluctuating, fatigable weakness of ocular, bulbar, and limb muscles. Diagnosis rests on antibody testing and electrodiagnostics; first-line treatment is pyridostigmine, with glucocorticoids and steroid-sparing immunosuppression for generalized disease and thymectomy for eligible patients.
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What this article covers
- Overview
Autoimmune neuromuscular junction disease: myasthenia gravis (MG) is caused by antibodies against the postsynaptic membrane of the neuromuscular junction, most commonly the acetylcholine receptor…
- Epidemiology
Bimodal age and sex distribution: onset most commonly occurs in the third decade of life in women and after age 50 years in men.
- Risk factors
Female sex in young adulthood or male sex after age 50: the two demographic peaks of onset.
- Pathophysiology
AChR antibody-mediated receptor loss: IgG antibodies against the nicotinic acetylcholine receptor activate complement and accelerate receptor internalization and destruction at the postsynaptic…
- Clinical features
Fluctuating, fatigable, painless weakness without sensory loss: the cardinal clinical picture; weakness characteristically worsens with sustained or repeated activity and toward the end of the day, and improves with rest.
- Differential diagnosis
Myasthenic crisis: not a separate diagnosis but the acute respiratory-failure exacerbation of MG; distinguished by the presence of hypoxemia/hypercapnia and the need for ventilatory support, addressed as its own emergency.
- Diagnosis
The diagnosis is established by the combination of a compatible fatigable weakness pattern with a positive disease-specific autoantibody and/or a decremental electrodiagnostic response…
- Management
Start pyridostigmine for symptomatic control of ocular or mild generalized disease: pyridostigmine 30-60 mg PO every 4-6 hours, titrated to symptom control (usual ceiling around 120 mg per dose, not…
- Complications
Myasthenic crisis: rapid, life-threatening respiratory failure requiring intensive monitoring and ventilatory support; can arise spontaneously or be triggered by infection, surgery, or precipitating medications.
- Prognosis
Good functional outcomes with treatment: most patients achieve substantial symptom control or remission with pyridostigmine, immunosuppression, and thymectomy when indicated; near-normal life expectancy is expected with adequate treatment.
- Prevention
No primary prevention exists for this autoimmune disease.
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- Myasthenic crisis
Myasthenic crisis is acute, life-threatening respiratory and bulbar failure from severe worsening of myasthenia gravis, distinct from the chronic, ambulatory disease. Diagnosis rests on bedside respiratory monitoring (vital capacity, maximal inspiratory pressure) and distinguishing it from cholinergic crisis (anticholinesterase overtreatment); management is airway protection plus IVIG or plasma exchange.
- Guillain-Barre syndrome
Guillain-Barre syndrome is an acute, post-infectious autoimmune polyradiculoneuropathy causing rapidly progressive ascending flaccid weakness and areflexia. Diagnosis is clinical, supported by albuminocytologic dissociation on CSF and demyelinating changes on electrodiagnostic studies; first-line treatment is IVIG or plasma exchange with close monitoring for respiratory failure.
- Botulism
Botulism is a descending, symmetric flaccid paralysis caused by Clostridium botulinum neurotoxin, which blocks presynaptic acetylcholine release at the neuromuscular junction and autonomic synapses. Diagnosis is clinical, supported by toxin assay of serum, stool, or wound, and management is early antitoxin administration plus supportive respiratory care, since antitoxin halts progression but does not reverse existing paralysis.