Selective disappearance of medial back muscles in a case of myotonic dystrophy type 1

Here, we report a unique case of late-onset myotonic dystrophy type 1 in a 64-year-old woman, with selective disappearance of the medial lower back muscles. We compared the clinical features of this patient with those of a cohort of 29 patients with myotonic dystrophy type 1 to clarify the correlation between clinical features and lower back muscle atrophy. After classification into three subgroups according to muscle atrophy pattern, medial muscle atrophy was present in 17.2% of the patients. Affected patients were older at onset than non-affected patients, and limb muscle power and respiratory function decreased with atrophy progression.