Daytime serum myoglobin fluctuations in Steinert's disease.

Baseline and evening serum myoglobin levels have been measured in 14 patients with Steinert's myotonic dystrophy. Mean levels in the morning and after a day of habitual activities, were higher in the study group than in a control group of healthy males. Serum levels in dystrophic patients were higher in the evening determinations, especially in the working patient subgroup. It is concluded that the daily physical effort of a normal job, significantly increases the serum myoglobin levels in patients with Steinert's disease.