Clinical correlates of obstructive sleep apnoea in idiopathic normal pressure hydrocephalus

Abstract Background and purpose The pathogenesis of idiopathic normal pressure hydrocephalus (iNPH) remains controversial. Limited studies have indicated a high prevalence of obstructive sleep apnoea (OSA) amongst iNPH patients. The aim was to investigate the clinical correlates of OSA in iNPH patients. Methods In this cross‐sectional observational study, consecutive iNPH patients were prospectively enrolled. Evaluations included the iNPH Rating Scale, the Movement Disorder Society Unified Parkinson's Disease Rating Scale part III, the time and number of steps to walk 10 m, the Epworth Sleepiness Scale, the Pittsburgh Sleep Quality Index, a complete neuropsychological evaluation, 3‐T brain MRI, full‐night video‐polysomnography, tap test and cerebrospinal fluid (CSF) neurodegeneration biomarkers. Results Fifty‐one patients were screened, of whom 38 met the inclusion criteria. Amongst the recruited patients, 19/38 (50%) exhibited OSA, with 12/19 (63.2%) presenting moderate to severe disorder. OSA+ iNPH patients required more time ( p = 0.02) and more steps ( p = 0.04) to complete the 10‐m walking test, had lower scores on the gait subitem of the iNPH Rating Scale ( p = 0.04) and demonstrated poorer performance on specific neuropsychological tests (Rey Auditory Verbal Learning Test immediate recall, p = 0.03, and Rey–Osterrieth Complex Figure, p = 0.01). Additionally, OSA+ iNPH patients had higher levels of total tau ( p = 0.02) and phospho‐tau ( p = 0.03) in their CSF but no statistically significant differences in beta‐amyloid (1–42) levels compared to OSA− iNPH patients. Conclusion Obstructive sleep apnoea is highly prevalent in iNPH patients, particularly at moderate to severe levels. OSA is associated with worse motor and cognitive performance in iNPH. The CSF neurodegeneration biomarker profile observed in OSA+ iNPH patients may reflect OSA‐induced impairment of cerebral fluid dynamics.