Two weeks of twice-daily prism adaptation treatment does not improve posture or gait in Parkinson's disease: a double-blind randomized controlled trial

Background: Gait difficulties in Parkinson's disease have been related to problems shifting the center of gravity forward. We previously showed reduced forward stepping latencies for people with Parkinson's disease after one session of adaptation to upward visual shifts, which produces downward motor after-effects and potentially shifts the center of gravity forward. Here we tested if repeated prism adaptation improved gait and postural control in Parkinson's disease through a parallel, double-blind, randomized, sham-controlled trial. Methods: We recruited participants with idiopathic Parkinson's disease aged 40-85 and meeting any one of three clinical criteria: (1) Hoehn and Yahr Stage II.5-IV; (2) scoring > 0 on the gait, freezing of gait, and/or postural stability items of the Movement Disorder Society Unified Parkinson's Disease Rating Scale; or (3) Timed Up and Go > 12 s. Sealed envelope style randomization allocated participants to two weeks of twice-daily prism adaptation or sham treatment. Participants, care givers, and those assessing the outcomes were blinded to group assignment. Primary outcomes were changes in postural control measured using the Berg Balance Scale and the Limits of Stability, Sensory Organization, and Motor Control tests from the Smart EquiTest system. Secondary outcomes included other physiotherapy and questionnaire measures. Outcomes were assessed at the Dartmouth Hitchcock Medical Center immediately before and after the treatment period, with further long-term postal follow-up over 3 months. Outcomes were analyzed using analyses of variance with follow-up t tests. Results: Eighteen participants were allocated to undergo prism adaptation, of which sixteen were analyzed. Thirteen participants were allocated to undergo sham treatment, and all were analyzed. The prism adaptation group showed increased forward stepping velocity on the Limits of Stability test (pre: M=2.33, SEM=0.24; post: M=2.88, SEM=0.26; t(15)=3.2, p=.005, d=.819). The sham group showed no such change (pre: M=2.13, SEM=0.22; 1d post: M=2.24, SEM=0.22; t(13)=.636, p=.537, d=.176). However, there were no group differences for any other outcome measures and no indications that prism adaptation produced functional improvements in posture, gait, or activities of daily living. Conclusions: Prism adaptation does not improve gait or postural control in Parkinson's disease.