Myasthenia Gravis in Pregnancy

Myasthenia gravis in pregnancy is autoimmune neuromuscular junction disease causing fluctuating, fatigable muscle weakness, in a pregnant woman. Course in pregnancy is unpredictable: about one third improve, one third worsen and one third are unchanged, with worsening common in the first trimester and after delivery. Maternal antibodies cross the placenta and cause transient neonatal myasthenia in some babies.

• Risk factors for crisis: infection, surgery, stopping drugs, magnesium sulphate, certain antibiotics.
• Respiratory muscle weakness is the main danger.
• Delivery needs coordination between obstetric and anaesthetic teams.

Women have drooping eyelids, double vision, difficulty chewing, swallowing and speaking, limb weakness and breathlessness, worse after activity and at the end of the day. Examine eyes, bulbar function, neck flexors and breathing.

• Fatigable ptosis on sustained upgaze.
• Weak cough and reduced vital capacity in crisis.
• Differential diagnosis: Guillain-Barre syndrome, botulism, thyroid disease, stroke, polymyositis, motor neurone disease, Lambert-Eaton syndrome.
• Complications: myasthenic crisis, respiratory failure, aspiration, preterm birth, neonatal myasthenia, arthrogryposis in rare cases.

The approach is clinical, with antibody tests and monitoring of lung function.

• Acetylcholine receptor antibodies and muscle specific kinase antibodies.
• Single fibre or repetitive nerve stimulation electromyography; edrophonium or ice pack test where available.
• Forced vital capacity (below 20 mL/kg or falling by 30 percent signals risk), TSH and free T4, chest X-ray with shielding for thymoma.
• Fetal growth scans and monitoring.

The principle is to continue effective treatment, avoid drugs that worsen weakness and protect breathing in labour.

• Supportive: avoid overexertion and infection; plan delivery in a facility with anaesthetic and intensive care; rest between meals; assistance with feeding; breastfeeding is allowed with careful timing of pyridostigmine.
• Pharmacological: pyridostigmine 30 to 60 mg oral every 4 to 6 hours while awake (maximum 360 mg daily), increased slowly, and given 30 to 60 minutes before meals; IV pyridostigmine is one thirtieth of the oral dose; prednisolone 20 to 40 mg oral daily, increased slowly to 60 mg daily, with calcium carbonate 1 g oral daily and vitamin D 1000 IU daily; azathioprine 2 mg/kg oral daily may continue; for crisis give immunoglobulin 0.4 g/kg IV daily for 5 days or plasma exchange on alternate days for 5 sessions; avoid magnesium sulphate (use levetiracetam 500 mg oral or IV 12-hourly for seizure control if needed), aminoglycosides, fluoroquinolones, macrolides, beta blockers and neuromuscular blockers; avoid methotrexate and mycophenolate.
• Procedures: forceps or vacuum assistance for the second stage if maternal pushing is weak; caesarean section only for obstetric reasons; epidural analgesia is preferred; thymectomy only after delivery.
• Special groups: neonates are observed for 48 hours for weakness, weak cry and poor feeding, and treated with neostigmine 0.05 to 0.1 mg IM before feeds if needed; women with preeclampsia need nifedipine 10 to 20 mg oral 8-hourly and, if magnesium is unavoidable, careful monitoring of respiratory function.
• Red flags: breathing difficulty, weak cough, swallowing difficulty, forced vital capacity falling, rising pyridostigmine need, drug triggers.
• Follow-up: review every 2 to 4 weeks; neurology review each trimester; postpartum review at 1 week and 6 weeks; neonatal review daily for 2 days.