Objective:

Assess the risk factors and geographic distribution of idiopathic normal pressure hydrocephalus (NPH) in the United States (U.S.).

Background:

The etiology and healthcare burden of NPH in the U.S. is unknown. Population-based studies, such as those using Medicare data, have the potential to address that knowledge gap.

Design/Methods:

Using Medicare beneficiaries from 2017-2018, we conducted a case-control study of incident NPH cases (n=5,573) and matched controls (n=34,467), excluding cases with shunts or diagnoses indicative of secondary hydrocephalus. We calculated the odds ratios (ORs) and 95% confidence intervals (CIs) for all ICD-10 diagnosis codes in the year prior to NPH diagnosis or control reference date, adjusted for demographics (sex, age, race, healthcare utilization, and smoking), and applied Bonferroni correction. Diagnoses for significant ICD-10 codes were grouped based on clinical similarity and odds ratios for groups were recalculated. County-level standardized incidence ratios (SIRs) were calculated adjusting for sex, age, and race, and then mapped with spatial smoothing. Bivariate local indicators of spatial association (BiLISA) analysis was used to evaluate the relationship between SIRs and the density of neurosurgeons.

Results:

NPH cases were more likely to be older (p<0.01), male (p<0.01), and smokers (p<0.01). Diagnosis codes for cognitive impairment (OR=5.66, 95% CI:5.31-6.05), movement disorders (OR=5.13, 95% CI:4.81-5.47), urinary incontinence (OR=2.00, 95% CI:1.88-2.14), insomnia (OR=1.51, 95% CI:1.33-1.71), mental health disorders (OR=2.14, 95% CI:1.99-2.29), and cardiovascular disease (OR=1.30, 95% CI:1.22-1.39) were positively associated with NPH. Higher SIRs were observed in Southern California, Florida, and Texas. BiLISA results showed SIRs in these regions were positively correlated with the density of neurosurgeons.

Conclusions:

Prodromal NPH symptoms and cardiovascular disease are strongly associated with incident NPH diagnosis. NPH incidence varies regionally, but many high incidence regions are correlated with local neurosurgical expertise.