A 31-year-old woman gave birth to a hypotonic baby.

This 31-year-old woman gave birth to a floppy baby 2 weeks earlier. Although the mother has no past neurological or neuromuscular history of symptoms, simple observation demonstrates classic features of myotonic dystrophy with a myopathic lugubrious facies and mild eyelid ptosis. In addition, the patient demonstrates a classic grip and percussion myotonia. In men, the diagnosis can be even more obvious given the presence of frontal balding. Ninety percent of patients have posterior subcapsular cataracts. Myotonic dystrophy typically produces substantial distal extensor muscle weakness, often more pronounced than in proximal muscle groups.