BACKGROUND AND PURPOSE: Patients with myotonic dystrophy type 1 (DM1) have an increased incidence of endocrine dysfunction. In this study, the temporal evolution of endocrine dysfunction in patients with DM1 was investigated.

METHODS: Endocrine function was assessed in 68 patients with DM1, in whom endocrine function had been followed, on average, for 8 years. The endocrine function was assessed by measuring the concentration of hormones and metabolites in blood and by validating libido with questionnaires.

RESULTS: At baseline, 30 of the 68 patients presented with at least one hormonal dysfunction. When re-evaluated after 8 years, 57 of 68 patients had endocrine dysfunction. Diabetic patients had increased from one to four. At follow-up, hyperparathyroidism occurred in 25% and abnormal thyroid-stimulating hormone in 21%, compared with 14% and 9% at baseline. Sixteen of 33 men had increased luteinizing hormone levels compared with seven at baseline.

CONCLUSIONS: Our findings show that endocrine abnormalities amongst patients with DM1 increase over time. Based on these findings it is suggested that correctable endocrine abnormalities should be monitored periodically in this patient group.