Disruption of sleep-wake continuum in myotonic dystrophy type 1: Beyond conventional sleep staging

Sleep disruption and excessive daytime sleepiness are well recognised symptoms in myotonic dystrophy type 1 (DM1), where a central dysfunction of sleep-wake regulation may play a pivotal role. Few studies evaluated sleep macrostructure in DM1, but none investigated more refined sleep variables. Eight DM1 patients (6 male, aged 20-50 years) and 10 healthy controls (7 male, aged 22-67 years) underwent nocturnal polysomnography and multiple sleep latency test. Sleep stages and events were scored according to standard criteria; sleep microstructure was analyzed through cyclic alternating pattern. Relative and absolute delta powers were computed for whole non REM and each non REM period. DM1 patients showed increased REM sleep and decreased N2. N3, although not significantly, was increased. Three patients, but no controls, had sleep-onset REM period in nocturnal sleep. DM1 patients showed slower delta power dissipation across the night, and increased sleep instability (CAP rate). Multiple sleep latency tests showed shorter sleep latencies, five patients presenting at least one sleep-onset REM period and, when including also night sleep, two sleep-onset REM periods. Our data confirm a narcoleptic-like phenotype in DM1 with a prominent REM sleep dysregulation, that may account for daytime sleepiness, together with increased sleep instability and impaired delta power dissipation that seem peculiar of the disease.