Supplementary Material for: Cutaneous Neoplasms in Myotonic Dystrophy Type 1

Background: The most frequent skin features associated with myotonic dystrophy type 1 (DM1) are frontal alopecia and pilomatrixomas. Several reports suggest that the incidence of basal cell carcinoma is increased in DM1. However, two recently published studies examining this topic have contradictory results. Objective: To retrospectively study the incidence of cutaneous tumours in patients with DM1. Methods: The clinical features of 102 Caucasian patients diagnosed with DM1 at Bellvitge Hospital in Barcelona, Spain, were retrospectively analysed. Clinical charts of the patients were reviewed, and cutaneous tumours diagnosed in our hospital were recorded. A group of 103 Caucasian patients matched for age and sex were used as the control group. Results: A total of 56 male and 46 female patients with DM1 were included in the study (mean age 49.07 years, SD 13.02). At least 1 basal cell carcinoma was diagnosed in 6 patients in the DM1 group versus 3 patients in the control group (p = 0.332). The mean age at diagnosis of the first basal cell carcinoma was 51 years compared with 66 years in the control group (p = 0.035). Five patients with DM1 presented pilomatrixomas versus none in the control group (p = 0.029). We did not detect any melanoma in our DM1 patients. Conclusion: Basal cell carcinomas appeared at a significantly younger age in our DM1 patients than in the general population, and this suggests that, at least in some patients, DM1 may predispose to the development of basal cell carcinomas.