Teaching NeuroImages: Myotonic dystrophy type 1.

A 51-year-old woman presented with 2 years' history of progressive distal weakness and muscle atrophy. Clinical and electrophysiological myotonia were found. MRI showed bilateral discrete and confluent areas of abnormal hyperintensity throughout the white matter with predominant involvement of the anterior temporal lobes and external capsules (figure). Genetic testing of DMPK revealed more than 50 CTG repeats in 1 allele, confirming the diagnosis of myotonic dystrophy type 1 (DM1). DM1 is the most common muscular dystrophy observed in adults.1 Though MRI in the late stage of DM1, CADASIL and mitochondrial myopathy may be similar, the clinical history for each condition is very different.2