REM sleep behaviour disorder in elderly subjects with epilepsy: frequency and clinical aspects of the comorbidity

To evaluate the clinical aspects of REM sleep behaviour disorder (RBD) occurring in elderly people with epilepsy, and the frequency of this comorbidity.

Eighty epilepsy patients aged 60 or over (47 men; mean age 70.7+/-7.1) were screened for episodes of RBD. Those whose clinical and video-polysomnographic findings met the relevant ICSD-2005 criteria received a definite diagnosis of RBD.

Undiagnosed or misdiagnosed episodes of idiopathic RBD were found to coexist with epilepsy in 10 out of the 80 (12.5%) subjects investigated. RBD occurred more frequently in the men (p<0.04) than in the women, and in those with cryptogenic epilepsy (p<0.05). The RBD episodes pre-dated seizure onset by 4.5 years in six subjects and post-dated seizure onset by 9.7 years in the others, and were more likely to occur in patients with sleep-related seizures.

Undiagnosed or misdiagnosed RBD can coexist with epilepsy in the elderly. Increased awareness of this potential comorbidity may help to prevent misdiagnosis and incorrect treatment of affected patients. The ultimate neurobiological meaning of the coexistence of RBD and seizures is still unclear. The two conditions could co-occur by chance; alternatively they may both be underlain by neurodegenerative processes. In cases of seizures during sleep the two disorders may, hypothetically, also show interactions (similarly to what has been documented in feline models of generalised and focal epilepsy with REM sleep "without atonia" and "without EEG desynchrony" induced by pontine dissociation techniques.