0790 Clinical and Demographic Characteristics of Isolated REM Sleep Behaviour Disorder with and Without Obstructive Sleep Apnoea

Abstract Introduction Isolated rapid eye movement (REM) sleep behaviour disorder (iRBD) is characterised by dream-enactment behaviours and loss of muscle REM atonia on polysomnogram (PSG) and represents a prodromal marker of α-synucleinopathies (e.g. Parkinson’s disease; PD). Obstructive sleep apnoea (OSA) involves recurrent upper airway collapse and intermittent hypoxia. OSA has been linked to neurodegeneration, with reports of increased α-synuclein levels in OSA patients, and is proposed as an independent predictor of PD. iRBD and OSA frequently coexist yet their interaction remains unclear. This study assesses demographic and clinical differences in iRBD patients, with and without OSA. Methods Patients with PSG-confirmed iRBD and symptom onset ≥45 years were included from our Sleep Disorders Centre. OSA was defined as apnoea-hypopnoea index (AHI) ≥5 events/hour at iRBD diagnosis. Demographic, clinical, and PSG data were collected from electronic records. Results are presented as mean±standard deviation, unless otherwise specified. Results 205 individuals were included (age 68.1±7.8 years, 82.4% male); age at iRBD diagnosis 65.4±7.4 years; 91 (44.4%) had OSA (overall AHI 17.1±12.8, 20% severe). Kaplan–Meier analysis showed that, over 2.68±2.85 years, 13.7% of patients phenoconverted. In the OSA group, BMI was higher (29.2±4.7 vs 27.0±4.3 kg/m2, p=0.001), sexual dysfunction was more common (50.0% vs 32.6%, p=0.033), and hyposmia was less prevalent (51.1% vs 65.7%, p=0.042). Individuals with sexual dysfunction spent more sleep time with SpO2 90% (8.8±21.6 vs 1.5±5.0%, p=0.011), had lower mean nocturnal SpO2 (93.7±2.1 vs 94.5±1.5%, p=0.005) and higher oxygen desaturation index (9.4±12.1 vs 5.4±7.2, p=0.023). Within phenoconverted patients, 39% had OSA; time from iRBD diagnosis to phenoconversion was similar between groups (non-OSA 5.2±3.8 vs OSA 4.4±3.7 years). On adjusted multivariate analysis, lower mean nocturnal SpO2 was independently associated with cognitive dysfunction at baseline (OR 1.09, p=0.009). Conclusion In iRBD, OSA is highly prevalent and associates with higher BMI, sexual dysfunction and less hyposmia. OSA may contribute to dysautonomia features, such as sexual dysfunction in iRBD. No significant differences were observed in proportion or time to phenoconversion between groups. Nocturnal hypoxia may relate to increased odds of cognitive dysfunction. Longitudinal studies with longer follow-ups are warranted to clarify clinical differences and prognostic implications of OSA in iRBD. Support (if any)