Myasthenia Gravis
Autoimmune mediated destruction of the postsynaptic NMJ.
Clinical Presentation
Fatiguable weakness in young women in their 20s and older men in their 60s:
| Group | Presentation |
|---|---|
| Ocular | Ptosis, binocular diplopia, pupil-sparing |
| Bulbar | dysarthria, dysphagia, chewing fatigue, head drop |
| Respiratory | orthopnea |
| Extremities | proximal > distal weakness, intense fatigue |
Myasthenic Crisis
Elective Intubation
Consider for the 20-30-40 rule as described for Guillain-Barré Syndrome. Essentially, if FVC < 20 mL/kg, absolute MIP less than 30 cm H2O, absolute MEP < 40 cm H2O, consider early intubation.
Immunosuppressive Agents
- PLEX (preferred due to rapidity of action), vs
- IVIg (2 g/kg over 2-5 days)
Hold pyridostigmine while intubated (for airway secretion management). Consider high-dose prednisone (can cause transient worsening of respiratory status within the next 5-10d)
Maintenance Treatment of MG
Symptomatic Therapy
Pyridostigmine 60 mg PO TID - causes GI upset, bronchorrhea, cholinergic effects
Disease Modifying Therapy
- Prednisone - the lowest effective dose.
- Azathioprine or MMF
- Maintenance PLEX
- Maintenance IVIg
- Eculizumab - needs vaccination against encapsulated organisms
Thymectomy
Refer to thoracic surgery for the 10% of patients with a thymoma. If the patient does NOT have a thymoma, consider elective thymectomy if under age 60, AChRAb+, or if disease duration is less than 5 years (essentially, early and young).