Laughing as a manifestation of rapid eye movement sleep behavior disorder

Abstract Background Among the range of sleep-related behavior displayed by patients with rapid eye movement (REM) sleep behavior disorder (RBD), aggressive acts are particularly common, while pleasant behaviors have rarely been reported. We aimed at identifying the frequency and characteristics of patients who displayed laughing as a pleasant, nonviolent manifestation of RBD. Methods We reviewed 67 consecutive polysomnographic recordings of patients with RBD, obtained in our sleep laboratory between July 2004 and July 2009. Results We identified 14 patients (21% of our RBD patients with degenerative parkinsonism: 10 males, mean age 63 ± 11 years) who repeatedly laughed during REM sleep. Ten patients had idiopathic Parkinson’s disease, 3 suffered from multisystem atrophy and 1 patient was diagnosed with dementia with Lewy bodies. Other RBD-associated behaviors included smiling, crying, aggressive behavior, screaming, and somniloquia. Nine of the 14 patients were depressed during daytime. Conclusion Laughing belongs to the spectrum of behavioral manifestations of RBD. Many of our patients with RBD-associated laughter were depressed, suggesting a dissociation between emotional expression during daytime and REM sleep.