Dopaminergic imaging separates normal pressure hydrocephalus from its mimics

Idiopathic normal pressure hydrocephalus (iNPH) and iNPH mimics (i.e., Parkinson's disease, progressive supranuclear palsy or dementia with Lewy bodies) share similar clinical features, and discrimination between both conditions relies on invasive time-consuming investigations. This study aims to compare [¹²³I]FP-CIT SPECT imaging-visual rating and semiquantitative values-between iNPH and iNPH mimics.

Among 56 patients with a suspicion of iNPH (76.5 ± 6.1 years; 23.2% women), 26 fulfilled the iNPH diagnostic criteria and the remaining 30 were classified as iNPH mimics. Patients were visually categorized as having normal or abnormal [¹²³I]FP-CIT SPECT; and for the quantification of the [¹²³I]FP-CIT SPECT imaging, we calculated striatal binding ratios (SBR) using BRASS™ automated brain analysis while applying locally established reference limits (adjusted for age). Logistic regressions were used to assess the association between [¹²³I]FP-CIT SPECT and diagnostic groups.

A normal SBR [¹²³I]FP-CIT SPECT was present in 69.2% of iNPH and 37.9% of mimics (p value = .020), while visual rating did not differ between the two groups. Normal SBR [¹²³I]FP-CIT SPECT values were associated with the diagnosis of iNPH, even after adjusting for white matter changes and comorbidities (adjusted odds ratio: 4.17; 95% CI 1.26-13.80).

Semi-quantitative [¹²³I]FP-CIT SPECT evaluation, but not visual assessment, discriminates iNPH patients from their mimics. [¹²³I]FP-CIT SPECT represents an interesting neuroimaging biomarker to improve the selection of patients with iNPH for invasive shunt surgery.