Postural instability is a frequent symptom of patients with idiopathic normal pressure hydrocephalus (iNPH), and might be due to the misperception of body verticality. The objective of this study was to assess the usefulness of the subjective body vertical (SBV) as a potential tool for diagnosing iNPH. Twenty patients with iNPH underwent tests of SBV in the pitch and roll planes before and after cerebrospinal fluid (CSF) drainage. Ten patients with other central gait disorders served as controls and also underwent tests for SBV. Before CSF drainage, patients with iNPH showed an impaired verticality perception in the pitch plane with a significant backward deviation of the SBV as compared to the control group (iNPH: mean ± SD -3.7 ± 3.6°; control group: -0.8 ± 2.2°; t value = -2.30, p t-test = 0.03). After CSF drainage, the SBV of the iNPH patients normalized for the pitch plane (-0.9 ± 1.9°). There was a correlation between the backward deviation of the SBV and the ventricular enlargement of the frontal horns (Evan's index; r = -0.52; p Pearson = 0.02). An even stronger correlation was found with the enlargement of the third ventricle (Thalamus index; r = -0.64; p Pearson = 0.002). The new and clinically relevant finding of this study is that verticality perception of patients with iNPH is primarily impaired the pitch plane, and it improves after CSF drainage. This disturbance in pitch might be due to a bilateral central vestibular dysfunction of the thalamus. Determination of the SBV in pitch promises to increase diagnostic accuracy in the cases of suspected iNPH.
Keywords: Falls; Idiopathic normal pressure hydrocephalus; Posture; Thalamus; Verticality perception.