LAUSR

Introduction It has been recently hypothesized that Pisa syndrome (PS), the most dramatic form of lateral trunk tilt occurring in persons with PD, might be caused by a bias in one of the key spatial referential. Despite many recent papers, this issue remains to be solved. This study is the first to comprehensively investigate the representation of the vertical (2 modalities: visual [VV] and postural [PV]), together with the representation of the long body axis (LBA) in a group of PD patients with PS. Methods The study consisted in a double-blind controlled trial manipulating conditions of deep brain stimulation (DBS) in 18 PD participants (63.4 [5] years, 11 females, disease duration 18.5 [4.7] years) treated with bilateral DBS of the subthalamic nuclei (STN) (11.8 [2.9] years postdiagnosis) and presenting with a PS. VV, PV and LBA were tested off medication under four condition of STN stimulation (bilateral on, bilateral off, unilateral on/off, unilateral off/on). Motor state (UPDRS), scoliosis and lateral trunk tilt were also precisely assessed. Twenty healthy age- and gender-matched participants were also included (61.4 [6.4] years, 12 females, P = 0.36 and P = 0.94). Results The median lateral trunk tilt was 7.6°(5.5) when patients were instructed to stand as upright as possible. Scoliosis prevalence was high (71%) with a mean Cobb angle 18.8°(7.6). No link was found between the side of the PS and the asymmetry of denervation at the onset of the disease (10/18 tilted to the side of the most denervated striatum) or asymmetry of current symptoms (11/18 tilted toward the most affected hemibody). Spatial referential were more frequently biased in PS than in controls (P < 0.05): VV 7/18; PV 4/18; LBA. Transmodal vertical biases (VV + PV) were rare: 2/18. A possible causal relationship between any of these biases and PS was found in only 3 participants. No statistical rule was found between any of biased referential (side or magnitude) and the trunk tilt (side or magnitude). No spatial referential was modulated by DBS. Discussion–conclusion If VV, PV and LBA are frequently biased in PD persons with PS, this is not the origin of their lateral trunk tilt.