Parasomnia overlap disorder: A distinct pathophysiologic entity or a variant of rapid eye movement sleep behavior disorder? A case series

Background: Parasomnia overlap disorder (POD) currently is classified by the International Classification of Sleep Disorders, Second Edition (ICSD-2) as a variant of rapid eye movement (REM) sleep behavior disorder (RBD), and therefore its diagnosis also implies counseling the patients on the increased risk for developing neurodegenerative disorders. POD pathophysiology is not clear to date. Methods: The authors report 5 cases of POD, review the literature, and analyze previously published cases of POD. Results: In all 5 reported cases sleep-related activity was clearly demonstrated, though the RBD component was mild or incidentally discovered. None of the patients had Parkinsonian clinical features. Based on ICSD-2 criteria, there are 139 more POD cases reported in the literature and 69. 2% are idiopathic. The POD patients had an earlier age of onset than the patients with RBD. The RBD component was milder than the disorder of arousal (DOA) in most cases. Recently an updated classification was published, which included new categories of POD. The features mentioned above and the revised classification suggests that POD is not just a subtype of RBD. Conclusions: We propose that POD is a distinct pathophysiologic parasomnia. Further research to identify the underlying mechanism is needed. Proper counseling is necessary for patients presenting with POD at a young age of onset.