Myasthenia Gravis: Treatment

Myasthenic crisis is a life-threatening, rapid worsening of myasthenia gravis (MG) leading to respiratory failure requiring intubation or noninvasive ventilation. Impending crisis is rapid clinical worsening that could lead to crisis in days to weeks. Respiratory function must be closely monitored in patients with worsening myasthenic symptoms, as rapid deterioration can occur (see Chapter 60 ). Myasthenic crisis (or impending crisis) should be treated with either intravenous immunoglobulin (IVIg, 2 g/kg per day for 5 days) or plasmapheresis (three to five exchanges over 1–2 weeks), with the choice of therapy based on comorbidities and institutional availability. Plasmapheresis is probably more effective in patients with anti–muscle-specific kinase (MuSK) antibodies. Corticosteroids (prednisone 1 mg/kg daily) or nonsteroidal immunosuppressive therapies (such as azathioprine) may be started to control MG after the effects of IVIg or plasmapheresis have worn off. However, high-dose oral corticosteroids may transiently worsen myasthenic symptoms shortly after initiation so, in patients not already intubated, should generally be avoided until several days after initiation of IVIg or plasmapheresis. Alternatively, they may be started at a low dose (e.g., prednisone 10–20 mg daily) and gradually increased by no more than 5 mg every 3–5 days ( Table 98.1 ).

Table 98.1

Medications Commonly Used in Myasthenia Gravis

Medication	Starting dose	Titration	Maximum dose
First-line Therapies
Pryridostigmine	30 mg tid	Add 30 mg per dose q5–10 days. Extended release form can be added 180 mg qhs.	1500 mg daily; doses > 120 mg q3–4 h often cause side effects
Prednisone	10–20 mg daily	Increase no faster than 5 mg q3–5 d	1 mg/kg daily or 100 mg daily
Steroid-sparing Immunosuppressants
Azathioprine	50 mg daily	Increase by 50 mg q1–2 wk	3 mg/kg daily
Cylcosporine	100 mg bid	Increase by 0.5 mg/kg per day q2–4 wk to achieve trough serum level 75–150 ng/ml	3–6 mg/kg divided bid
Mycophenolate mofetil	500 mg bid	Increase by 500 mg bid q2–4 wk	1000–1500 mg bid
Tacrolimus	3 mg daily or 0.1 mg/kg per day in 1–2 divided doses	Titrate to achieve a trough concentration of 7–8 ng/mL	–