Objective: We compared iRBD versus secondary RBD due to narcolepsy, searching for discriminating clinical, neurophysiological and pathological biomarkers.

Background: Idiopathic REM sleep behavior disorder (iRBD) has the highest positive predictive value for impending neurodegeneration due to p-alpha-synuclein deposits, while the significance of RBD within narcolepsy is still poorly understood.

Method: Seventeen adults’ patients with NT1 and RBD were compared with 30 age and sex-matched patients with iRBD. Both groups underwent extensive examinations with neuropsychological investigations, neuroimaging and skin biopsy looking for phosphorylated α-synuclein (p-α-syn) deposits. Whole-night video-polysomnography (v-PSG) was analyzed by two sleep experts for identifying simple and complex motor episodes during all sleep stages.

Results: Patients with iRBD reported more frequently an every-night occurrence of RBD episodes, which more often were reported to be violent. NT1 patients had more frequently simple motor episodes which occurred throughout the whole night, in all sleep stages and showed an “intra-individual” stereotyped pattern. IRBD patients instead had episodes confined to REM sleep and occurring predominantly in the second half of the night. Skin biopsy was positive for p-α-syn deposits in 86.7% of iRBD patients and in none of NT1 patients. Subtle abnormalities at neuropsychological investigation were more frequent in iRBD patients versus patients with RBD due to NT1.

Conclusion: iRBD and RBD due to NT1 do have different clinical and pathological findings, confirming a completely different pathophysiology. Both v-PSG and skin biopsy can discriminate between the two conditions.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/biomarkers-of-idiopathic-rem-sleep-behavior-disorder-versus-rbd-within-narcolepsy/