Altered central vestibular processing in Parkinson's disease with Pisa syndrome

In Parkinson's disease (PD) dizziness, imbalance, postural instability and impaired visuospatial orientation occur, about 10% of PD additionally present with Pisa syndrome (PS). Aim of the current study was (a) to evaluate the perception of verticality by subjective visual vertical (SVV) and visuospatial orientation by the Benton Judgement of Line Test (JLO) in PS, (b) to analyze vestibular reactivity after vestibular stimulation and (c) to compare isolated cervical dystonia (iCD) before and after botulinum neurotoxin (BoNT) treatment. Participants consisted of 20 PD patients (8 with PS), 32 iCD patients and 51 controls. All underwent a clinical examination, evaluation of JLO and SVV. JLO and SVV were tested before and after vestibular activation by galvanic vestibular stimulation (GVS). iCD patients were treated with BoNT and performed a second trial of the study protocol. PS had pathological deviations of SVV (SVV = 2.3 ± 0.7; F = 5.22, p = 0.002). After GVS this deviation further increased (SVV = 3.1 ± 0.9; F = 7.36, p < 0.001). The course of the SVV deviation induced by GVS differed significantly (rm-ANOVA: F = 6.09, p = 0.003), displaying a pathological response to vestibular activation in PS only. For iCD a significant decrease in JLO was detected after GVS (JLO = 11.4 ± 0.5; F = 2.82, p = 0.043). Finally iCD significantly improved after BoNT treatment, without an effect on SVV. PS patients have pathological perception of verticality. Since SVV deviations further increase in PS after GVS, this points to a pathological central processing of vestibular information. Therefore, PS may be associated with involvement of central vestibular and graviceptive pathways in PD.