High Evans Index in progressive supranuclear palsy may mimic normal pressure hydrocephalus: a retrospective cross-sectional study

Differentiating true normal pressure hydrocephalus (NPH) from neurodegenerative disorders with ex-vacuo ventriculomegaly remains a clinical challenge. Misdiagnosis can lead to inappropriate and risky shunt surgeries.

To evaluate the diagnostic utility of NPH-specific magnetic-resonance-imaging (MRI) markers, namely Evans Index (EI), callosal angle (CA), and disproportionatelyenlarged subarachnoid-space hydrocephalus (DESH) pattern, across different movement disorders.

In this retrospective cross-sectional study, we evaluated 125 consecutive patientsdiagnosed with Parkinson’s disease (PD, n = 43), essential tremor (ET, n = 43), dystonia (DYT, n = 19), and progressive supranuclear palsy (PSP, n = 20). Three movement disorder specialists measured the EI, CA, and DESH pattern on structural cranial MRIs. Kruskal-Wallis and Fisher’s exact tests were utilized for group comparisons.

The PSP group had a significantly higher median EI (0.27 ± 0.04) than PD (0.23 ± 0.02), ET (0.22 ± 0.02), and DYT (0.22 ± 0.02) (p < 0.001). Notably, EI exceeded the traditional NPH cutoff (> 0.3) only in the PSP group. However, the DESH pattern was absent in all 125 patients (0%). Furthermore, the median CA remained preserved (> 90°) across all groups (PSP: 123.5°, PD: 124.0°, ET: 126.0°, DYT: 129.0°), with no significant intergroup difference (p = 0.096). MMSE scores differed significantly among groups (p = 0.024).

Patients with PSP may demonstrate marked ventriculomegaly mimicking NPH. However, the absence of the DESH pattern and preserved CAs strongly indicate ex-vacuo hydrocephalus secondary to central atrophy rather than true NPH. Relying solely on the EI in movement disorders may lead to critical misdiagnoses.