Transient neonatal myasthenia gravis due to a mother with ocular onset of anti-muscle specific kinase myasthenia gravis.

We describe a 27-year-old pregnant female with new onset of conjugate gaze deficit during the third trimester of pregnancy. Repetitive nerve stimulation tests, neostigmine tests, and acetylcholine receptor antibody assays were all negative. The patient delivered a normal healthy baby at a local clinic via cesarean section. The baby became hypotonic and had respiratory failure several minutes after birth. The result of acetylcholine receptor antibody was negative in the neonate. The neonate became healthy spontaneously and was extubated after 21 days of ventilation care. Two months after delivery, the mother developed ptosis and generalized symptoms and subsequent workup revealed she was muscle specific kinase (MuSK) antibody positive. The neonate was presumed to have an anti-MuSK-mediated transient neonatal myasthenia gravis. Although MuSK antibody testing is rarely indicated in ocular myasthenia gravis, MuSK antibody testing is necessary in pregnant women who are presumed ocular myasthenia gravis to warn occurrence of transient neonatal myasthenia gravis.