Myasthenic Crisis With IgA Deficiency and Thymoma
61-year-old woman with 6 months of fluctuating ptosis and diplopia presents with 3 days of dysphagia and dyspnea. Anti-acetylcholine receptor antibodies are positive; chest CT shows a 4-cm anterior mediastinal mass consistent with thymoma. Vital capacity is 18 mL/kg, negative inspiratory force -22 cm H2O, and oxygen saturation 94% on room air. She takes pyridostigmine 60 mg every 4 hours and prednisone 20 mg daily. Serum IgA is undetectable (<7 mg/dL). The ICU team asks whether to use plasma exchange or IVIG, how to manage corticosteroids, and when thymectomy should occur.
1. Plasma exchange or IVIG for this crisis? Justify with her IgA deficiency and respiratory status.
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I would favor plasma exchange for this crisis. She has undetectable IgA, which raises the risk of an anaphylactic reaction to IVIG containing IgA, particularly if she has anti-IgA antibodies. PLEX removes pathogenic antibodies and is appropriate for severe bulbar and respiratory weakness. The usual course is five exchanges over 1–2 weeks, with monitoring for catheter complications, coagulopathy, and hemodynamic instability.
IVIG is not absolutely contraindicated; if PLEX is unavailable or access is poor, I would use an IgA-depleted IVIG product with allergy precautions. Her vital capacity of 18 mL/kg and NIF of -22 cm H2O place her near the threshold for intubation, so this decision should occur in the ICU with frequent respiratory monitoring rather than on a ward.
2. How would you adjust pyridostigmine and prednisone during the crisis?
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I would reduce or hold pyridostigmine during the acute crisis, especially if she is intubated or has copious secretions. Anticholinesterase drugs can worsen secretions and do not treat the underlying autoimmune attack; they are restarted cautiously during recovery. Prednisone should not be rapidly escalated without rescue therapy because high-dose corticosteroids can transiently worsen myasthenia. She is already on 20 mg daily; I would continue that or increase it only after PLEX or IVIG has been started, with close respiratory monitoring.
I would also monitor for steroid effects, treat electrolyte abnormalities, and avoid medications that impair neuromuscular transmission. The overall plan is rescue immunotherapy first, then gradual corticosteroid adjustment and thymoma management.
3. When should thymectomy be performed?
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Thymectomy should not be performed during the acute crisis. The priority is stabilization with PLEX or IVIG, respiratory support, and corticosteroid management. Once she is off mechanical ventilation, medically stable, and has recovered enough to undergo anesthesia, I would plan thymectomy, generally within weeks to a few months. Because she has a thymoma, resection is indicated for oncologic and myasthenic reasons.
Preoperative optimization may include another course of PLEX or IVIG, especially if weakness persists. I would involve thoracic surgery, anesthesia, and neurology in a joint plan rather than treating the thymoma as an emergency during respiratory failure.