Objective To examine the frequency and clinical features of excessive daytime sleepiness (EDS) and its association with cognitive and behavioural impairments in patients with amyotrophic lateral sclerosis (ALS).

Methods We conducted a cross-sectional investigation to explore the frequency and clinical features of EDS in a group of 121 Chinese patients with ALS compared with 121 age-matched and sex-matched healthy subjects. EDS was diagnosed using the Epworth Sleepiness Scale (ESS). Other characteristics of patients with ALS including sleep quality, REM sleep behaviour disorder (RBD), restless legs syndrome (RLS), cognition, behaviour, depression and anxiety were also evaluated.

Results EDS was significantly more frequent in patients with ALS than in controls (26.4% vs 8.3%; p<0.05). Patients with ALS with EDS scored lower scores on the revised ALS Functional Rating Scale (ALSFRS-R), Mini-Mental State Examination (MMSE), Montreal Cognitive Assessment (MoCA) and MMSE and MoCA delayed memory subitems and higher on the Frontal Behavioural Inventory (FBI) than patients with ALS without EDS. ESS scores correlated with global ALSFRS-R, FBI, MMSE and MoCA scores and MMSE and MoCA delayed memory scores. RLS and global ALSFRS-R scores were independently associated with EDS in patients with ALS.

Conclusions We identified a high frequency of EDS symptoms in Chinese patients with ALS, and these patients might have more serious physical, cognitive and frontal behaviour impairment. Patients with ALS might improve quality of life from the timely recognition and optimised management of EDS symptoms. Our results further suggest that ALS is a heterogeneous disease that might exhibit abnormal sleep-wake patterns.