Symptom Flares Common in MuSK-Positive MG, Case Series Shows

Women with myasthenia gravis (MG) with muscle-specific tyrosine kinase (MuSK) antibodies may see an increase in symptoms during pregnancy and may require more aggressive therapy during or after pregnancy, according to a new report.

However, the report—a case series of 14 pregnancies—also found that these patients are able to safely deliver healthy infants. The study was published in Muscle & Nerve.

Between 5% and 8% of cases of MG involve MuSK antibodies, and those patients most commonly experience weakness of the cranial, bulbar, and axial muscles. MuSK-positive MG (MMG) is similar to other forms of MG in that most cases are seen in women, but MuSK-associated cases tend to appear at an earlier age than other types of MG, wrote the study authors.

Previous research shows that MG can have an impact on the course of a pregnancy and vice versa, the authors wrote. Some infants of mothers with MG will even develop a transient form of the disease. However, most of what is known about MG and pregnancy is based on MG in general; there is little evidence looking specifically at outcomes among patients with MMG.

The new report is based on nearly 2 decades of cases from the Duke MG clinic, and the investigators looked at women whose MMG was diagnosed before, during, or within 6 months after pregnancy. The cases span from January 2003 to May 2021. The 14 pregnancies included in the analysis encompass 10 patients, since 4 patients in the study had 2 pregnancies during the study period.

In 8 cases, patients’ MG was diagnosed prior to them becoming pregnant. Five of those patients experienced an increase in their symptoms during their pregnancies or in the postpartum period, the authors said. Those rates are higher than previous studies.

“Several studies have reported increased MG symptoms in 20% to 40% of women with an unspecified type of MG during the first or second trimesters,” the authors said.

The other 6 patients experienced MG symptom onset during pregnancy or within 6 months of their pregnancies. Of the 4 patients with 2 pregnancies in the case series, 3 developed symptoms during their first pregnancy.

In 4 cases, symptoms reached the point where patients needed rescue therapy with plasma exchange (PLEx) or intravenous immunoglobulin during or after pregnancy. All 4 of those patients also needed mechanical ventilation, the authors said.

“Of note, all 3 of our patients who required PLEx developed severe bulbar dysfunction (MGFA [Myasthenia Gravis Foundation of American class IVB),” they noted. “These cases illustrate the importance of monitoring bulbar symptoms in women with MMG during pregnancy and in the postpartum period.”

However, although some patients experienced worsening symptoms, these did not impact outcomes. One patient delivered via cesarean section due to failure to progress, but none of the other pregnancies had complications, and all infants were healthy at birth.

The authors said the small sample size in their case series limits the generalizability of their findings and that a multicenter study would help clarify how MMG affects pregnancy. Until then, the authors said these cases offer insights clinicians can use to care for this patient group.

“Clinicians should be alert to changes in severity during pregnancy and postpartum as the manifestations of MMG at these time-points can be life-threatening,” they concluded.

Reference

Harada Y, Bettin M, Juel VC, et al. Pregnancy in MuSK-positive myasthenia gravis: a single-center case series. Muscle Nerve. Published online May 7, 2023. doi:10.1002/mus.27839