Magnesium Sulfate-Induced Myasthenic Crisis in Pregnancy: A Case Report

Myasthenia gravis (MG) is an autoimmune disorder characterized by antibodies targeting acetylcholine receptors (AChR) or muscle-specific kinase (MuSK) at the neuromuscular junction, resulting in fluctuating skeletal muscle weakness. Preeclampsia is an obstetric complication defined as new-onset hypertension and proteinuria, or new-onset hypertension with evidence of end-organ dysfunction with or without proteinuria, typically presenting after 20 weeks gestation or within six weeks postpartum. We report a 37-year-old woman at 19 weeks' gestation who developed a myasthenic crisis following administration of intravenous magnesium sulfate for suspected preeclampsia. When there is concern for preeclampsia in pregnant patients with MG, alternative treatments to magnesium sulfate should be utilized to avoid exacerbating or triggering a myasthenic crisis. In pregnant patients with MG, alternatives to magnesium sulfate should be considered for seizure prophylaxis and management because magnesium may precipitate or worsen myasthenic crisis. Hydralazine or nifedipine are considered first-line antihypertensive therapies in pregnant patients with MG; however, labetalol can also be used with caution because it may exacerbate MG symptoms.