Rest-activity disturbances and light exposure in myotonic dystrophy type 1 patients with apathy: An exploratory study using actigraphy

Background: Rest-activity rhythm disturbances have been reported in myotonic dystrophy type 1 (DM1) but no study has assessed its relationship with apathy and light exposure using actigraphy. Methods: Thirty-three DM1 patients wore an actigraph for two consecutive weeks. The Lille Apathy Rating Scale was used to assess apathy. Actigraphy was used to characterize sleep, activity, and light exposure and nonparametric analysis was performed to characterize intraday variability (IV), interday stability (IS), least active five-hour period (L5), most active ten-hour period (M10), and relative amplitude (RA). Results: Apathy was found in 42.4% of patients. Patients with apathy have a larger number of CTG repeat than those without (774 vs 381, p<0.01) Also, patients with apathy had higher IV values (0.98 vs 0.69, p<0.001) as well as lower IS (0.34 vs 0.47, p<0.05), RA (0.65 vs 0.83, p<0.05), and M10 (182.6 vs 493.8, p<0.001) values compared to patients without apathy. In addition, DM1 patients with apathy were exposed to less bright light (≥1000 lux) (41.4 vs 141.2 minutes p<0.01) than patients without. No difference was observed relatively to sleep quality and quantity. Conclusions: Daytime activity levels and bright light exposure were significantly lower in DM1 patients with apathy versus those without. The more fragmented, less stable, and lower amplitude rest-activity rhythm of DM1 patients with apathy, as revealed by non parametric analysis, can be partly ascribed to reduced daylight exposure. The use of bright light therapy as well as physical activity interventions should be explored to help prevent or reduce apathy levels in DM1.