Myasthenia gravis
Description
- Autoimmune disorder of the post-synaptic neuromuscular junction -> fatigable weakness
- Ocular (confined to lids and extraocular muscles) vs generalised
Serotypes - they behave differently
| % | Features | |
|---|---|---|
| AChR antibody | ~85% generalised, ~50% ocular | Classic phenotype; thymic pathology; responds to pyridostigmine |
| MuSK antibody | ~5-8% | F>>M, bulbar/facial/neck/respiratory predominant, tongue and facial wasting; poor or paradoxical response to pyridostigmine; no thymic pathology; excellent response to rituximab |
| LRP4 | 1-3% | Milder, often ocular |
| Seronegative | ~10% | Diagnosis rests on neurophysiology; check MuSK before calling it seronegative |
- Anti-striated muscle (titin, ryanodine receptor) antibodies -> think thymoma, especially in a patient <50
MGFA class
- I ocular only | II mild generalised | III moderate | IV severe | V intubation required
- Suffix a = limb/axial predominant, b = oropharyngeal/respiratory predominant
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