Most patients diagnosed with idiopathic REM sleep behavior disorder advance to a neurodegnerative disease associated with alpha synuclein deposition (Lewy body disease) within a decade.

Several longitudinal studies have demonstrated a consistent association between idiopathic rapid eye movement (REM) sleep behavior disorder (IRBD) and the development of neurodegenerative disorders associated with alphasynucleinopathy, including Parkinson disease (PD), dementia with Lewy bodies (DLB), and multiple systems atrophy (MSA). In one previously described cohort of 44 patients with symptomatic IRBD for a median interval of 11 years and followed clinically for a median of 4.5 years, 45% met criteria for a neurodegenerative disorder. Now, the investigators report their findings in this cohort after an additional 7-year interval.

The conversion to a defined neurodegenerative diagnosis was 82% (16 PD, 14 DLB, 1 MSA, and 5 mild cognitive impairment). Four cohort members were lost to follow-up. Three patients in the cohort underwent autopsy during the period of study, which demonstrated characteristic pathological changes confirming diagnoses of PD in 2 and DLB in 1. Compared with healthy controls without IRBD, 4 patients who did not meet criteria for a neurodegenerative disorder demonstrated decreased striatal uptake of dopamine transporter, a biomarker associated with alphasynucleinopathies.

Comment: Although the sample size is relatively small, this report emphasizes the importance of longitudinal observations in slowly progressive neurodegenerative disorders. The findings highlight an opportunity to identify at-risk individuals and potentially intervene as disease-modifying therapies become available. However, clinicians should look carefully for other causes of dream-enactment behavior, such as medications or concomitant sleep disorders. In the absence of such factors, clinicians should confirm the diagnosis with polysomnography. As the authors suggest, idiopathic RBD may be more accurately termedisolated RBD. Patients who have REM sleep behavior disorder but are asymptomatic for parkinsonism or dementia should be made aware of the risk and the need for continued clinical follow-up.

Source:Journal Watch Neurology