To describe the disease course of muscle specific tyrosine kinase (MuSK) positive myasthenia gravis (MMG) during pregnancy and the postpartum period.

Patients with MuSK antibodies comprise approximately 5-8% of all MG cases. Although MMG is predominantly seen in women of childbearing age, its disease course during pregnancy and the postpartum period has not been well described.

A retrospective review of the medical records of female patients with MMG seen in the Duke MG Clinic after 2003.

Ten patients with MMG who were pregnant during their course of MG were identified with a total of 14 pregnancies. Initial MG symptoms developed during pregnancy or within 6 months postpartum in 6/10 patients. Four patients had 2 pregnancies, 3 of whom developed MG during the first pregnancy. In the previously diagnosed patients, MG symptoms increased in 5/8 pregnancies.

Four patients required rescue therapy with plasma exchange or intravenous immunoglobulin during pregnancy. One patient had C-section after 14 hours of labor due to failure of delivery progression. There were no other complications of pregnancy or delivery, and all the babies were healthy at delivery. Four of 8 patients who underwent thymectomy before or after pregnancy had thymic hyperplasia.

As in non-MuSK MG, women with MMG may also have disease improvement or worsening, or develop initial MG symptoms during pregnancy or within 6 months postpartum. Among our patients, 4 required rescue therapy; pregnancy and delivery were not otherwise complicated by MG except for 1 patient who required C-section due to failure of delivery progression. Further study is needed to understand the mechanism and risk of worsening of MG during pregnancy or postpartum in MMG. Clinicians should pay attention to the changes of MG during pregnancy and postpartum as manifestations of MG at these times can be life-threatening.