Longitudinal study of cognitive function in idiopathic REM sleep behavior disorder

To assess the longitudinal course of cognitive functions in a cohort of patients with idiopathic REM sleep behavior disorder (iRBD).

Prospective study with baseline and 2-year follow-up.

Sleep disorders center.

Twenty-four cognitively asymptomatic iRBD patients (18 M; mean age: 69.5 ± 7.3 y) and 12 sex-, age-, and education-matched healthy subjects.

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.

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.

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.