Longitudinal Study of Cognitive Function in Idiopathic REM Sleep Behavior Disorder

STUDY OBJECTIVES: To assess the longitudinal course of cognitive functions in a cohort of patients with idiopathic REM sleep behavior disorder (iRBD). DESIGN: Prospective study with baseline and 2-year follow-up. SETTING: Sleep disorders center. PARTICIPANTS: Twenty-four cognitively asymptomatic iRBD patients (18 M; mean age: 69.5 ± 7.3 y) and 12 sex-, age-, and education-matched healthy subjects. INTERVENTIONS: Participants underwent to a video-PSG, a focused neuropsychological evaluation and a neurological examination. Following the first evaluation, subjects were reassessed after a mean interval of 25.8 months. MEASUREMENTS AND RESULTS: Executive functions, attention and language were normal at baseline and at 2 year follow-up examination. At baseline, iRBD patients showed poorer performance than controls in delayed verbal memory (story recall test: P = 0.001) and in visuo-constructional abilities (Copy of the Rey-Osterrieth complex figure: P = 0.0005). At follow-up, they not only performed worse than controls in the same tests (story recall: P = 0.0001; Copy of the Rey-Osterrieth complex figure: P = 0.0004), but they also showed an impairment in visuo-spatial learning (Corsi supraspan test; P < 0.0001). ANOVAs showed a significant worsening in visuo-spatial learning over time in RBD compared to controls (P = 0.0001). Furthermore, 3 patients fulfilled the UK Brain Bank criteria for Parkinson disease, but this was unrelated to cognitive deterioration. CONCLUSIONS: Although no patients developed dementia, the decline observed in some tests involving the memory and visuo-constructional domains in idiopathic RBD suggests the presence of an underlying evolving degenerative process.