Investigating Idiopathic Normal Pressure Hydrocephalus Prevalence and Comorbidity with Alzheimer's and Parkinson's: Ground Level Fall Rates and Shunting Efficacy

Introduction: Idiopathic normal pressure hydrocephalus (iNPH) prevalence estimates vary widely, and symptom overlap with Alzheimer’s (AD) and Parkinson’s diseases (PD) may delay or confound diagnosis. it is unclear how often these diseases occur together. This study offers the most extensive investigation of iNPH prevalence and comorbidity with AD and PD to date. Ground level falls (GLFs) are an important cause of morbidity in this demographic; GLF rates were compared in iNPH patients with and without AD or PD, before and after shunt placement.

Methods: Using the TrinetX database, we analyzed 39,601 elderly (60+ years old) patients diagnosed with iNPH out of 34,944,317 patients across 60 US Healthcare Organizations (2003-2023). Cohorts were matched for sex, age, ethnicity, race, and socioeconomic status. Acne (ICD-10: L70) was utilized as a control population. Data was analyzed using T-tests.

Results: Of the 0.11% of elderly patients diagnosed with NPH, 24.4% also had AD and/or PD. NPH, PD, and AD patients were 64.7%, 72.3%, and 39.2% more likely to fall than controls (all P<.001). In matched cohorts (n=~23,000), NPH patients were 22.3% and 4.6% more likely to experience a GLF than AD or PD patients respectively (P <.001, P=0.31). Of the 8,551 (28%) patients with only iNPH who had a shunt, the GLF prevalence was 18.9% in the 6 months pre-shunt and 15.5% in the 6 months post-shunt (P <.001). When iNPH was comorbid with AD or PD, shunting did not improve fall rates.

Conclusion : In the largest ever iNPH cohort, co-diagnosis of AD and/or PD was common. GLF rates in iNPH were higher than in AD and similar to PD. Shunting in iNPH cases reduced GLFs, but was ineffective in cases with comorbid AD or PD. These findings support therapeutic potential of shunting in iNPH and the need to further explore neurodegenerative comorbidities and improve diagnostic algorithms.