α-Synuclein Pathology in Idiopathic Normal Pressure Hydrocephalus: Evidence for Concomitant Synucleinopathy and Clinical Implications.

Idiopathic normal pressure hydrocephalus (iNPH) is a potentially reversible neurological disorder characterized by gait impairment, cognitive decline, and urinary dysfunction. Despite improvements in diagnostic criteria and neuroimaging techniques, accurate diagnosis remains challenging due to clinical overlap with neurodegenerative diseases, particularly Alzheimer's disease (AD) and synucleinopathies. Biomarkers capable of improving differential diagnosis, patient selection for shunt surgery, and prognostic assessment are therefore of considerable clinical interest, as has been in AD biomarkers. This review summarizes current evidence regarding the role of α-synuclein as a potential additional marker in iNPH, focusing on its association with concomitant neurodegenerative pathology, clinical manifestations, and treatment outcomes. Available studies indicate that α-synuclein pathology may coexist with iNPH in a substantial proportion of patients, with reported positivity rates ranging from approximately 14% to 33%, depending on the detection method used. Patients with concomitant α-synuclein pathology may exhibit clinical features atypical for pure iNPH, including upper limb rigidity, olfactory dysfunction, hallucinations, autonomic dysfunction, sleep disturbances, and fluctuating cognitive impairment. However, current evidence does not support α-synuclein positivity as an independent predictor of poor response to cerebrospinal fluid (CSF) drainage or shunt surgery. On the contrary, α-synuclein presence may provide additional information regarding mixed neurodegenerative pathology and contribute to personalized clinical management. Future studies should focus on standardized detection techniques, larger multicenter cohorts, longitudinal follow-up, and integration of α-synuclein assessment with established AD biomarkers, neuroimaging findings, and clinical evaluation. Overall, α-synuclein represents a promising complementary marker in iNPH, with potential value in being taken into consideration during clinical evaluation and understanding disease heterogeneity.