Case report of congenital myotonic dystrophy with multiple prenatal sonographic findings

Myotonic dystrophy 1 (DM1) is an autosomal dominant inherited neuromuscular disorder. The most severe form is congenital myotonic dystrophy (cDM). Prenatal diagnosis is complicated and sonographic findings of cDM that are not pathognomonic occur in the late second or early third trimester of pregnancy.

It is the case of prenatally diagnosed cDM. In 32 weeks of pregnancy multiple sonographic findings such as severe polyhydramnios, bilateral talipes, fetal legs akinesia, macrocephaly with mild bilateral ventriculomegaly, right-sided pleural effusion and diaphragmatic pathology were observed by fetal medicine specialist. As the patient complained of weakness in her limbs, she was consulted by a neurologist. The neurological examination revealed a pathognomonic sign of DM1 - grip myotonia. The amniotic fluid and the mother's blood sample were further tested for DM1. This identified >150 repeats in one copy of the DMPK gene of the both, which is consistent with the diagnosis DM1.

The sonographic findings of fetal limb abnormalities with progressive polyhydramnios is an indication for maternal neurological examination and genetic testing due to myotonic dystrophy.