Haptic perception of verticality correlates with postural and balance deficits in patients with Parkinson's disease

Introduction: Perception of verticality is fundamental for postural stability that is often impaired in patients with Parkinson's disease (PD). Haptic perception of verticality has not been fully investigated in PD. The aim of the study was to assess subjective haptic vertical (SHV) in PD patients in relation to postural and balance impairments. Methods: 39 PD patients (mean age 72.87 ± 5.78) and 28 gender and age-matched healthy elderly (ELD, mean age 69.16 ± 13.89) were enrolled. The Pull test and the Activities-specific Balance Confidence (ABC) were used for evaluating balance performance, whereas measurement of posture was performed using the Physical Analyzer System®. For evaluating SHV, participants were instructed to provide their subjective vertical by manipulating with two hands a road while standing with their eyes closed. Results: SHV data showed that PD subjects had a greater deviation from the objective vertical than controls (p < 0.001). Significant differences in balance performance (ABC and Pull test) and postural alignment were found between PD and ELD. Only in PD participants, SHV deviations significantly correlated with the lateral inclination of the trunk (r = 0.618, p < 0.001), pull test (r = 0.519; p = 0.001) and ABC (r = 0.471, p = 0.002) scores. Conclusions: The perception of verticality, driven by multimodal sensory integration, is defective in PD subjects. Deficits in SHV correlated with postural alignment and balance performances, independently from age, disease severity or cognitive decline. Our findings support that PD pathology is associated with a decline in haptic perception suggesting that perception per se might have a causal role in postural and balance deficits.