Association between Parkinson’s Disease subtypes and tests of physical function: the 360-degree turn test is most predictive

BACKGROUND AND PURPOSE People with Parkinson’s disease (PD) present phenotypes that can be characterized as tremor-dominant (TD) or postural instability / gait difficulty (PIGD) subtypes. Differentiation of subtypes allows clinicians to predict the disease course and adjust treatment accordingly. We examined whether brief mobility and balance measures can discriminate PIGD from TD phenotypes.

METHODS We performed a cross-sectional study with individuals with PD (N=104). Blinded raters assessed participants with the UPDRS or MDS-UPDRS, and potential predictor variables: 360-degree turn test, one-leg stance, backward perturbation test and tandem walk. Participant were classified as PIGD or TD based on the Unified Parkinson’s Disease Rating Scale or the Movement Disorder Society revision (UPDRS or MDS-UPDRS) assessment results. Differences in study variables between subtype groups were assessed with univariate analyses. Receiver operating characteristic (ROC) curve analyses were performed to investigate the ability of candidate predictor variables to differentiate PD subtypes.

RESULTS Mean age and disease duration were 68±9 and 7±5 years, respectively, and Hoehn & Yahr Stages I-IV median (1st,3rd quartile) = II (II, III). No differences between subtypes were observed for tandem walk or reactive postural control. PIGD participants performed worse on number of steps (p<0.001) and time to complete (p=0.003) the 360-degree turn test and one-leg stance (p=0.006). ROC curves showed only the 360-degree turn test could discriminate PIGD from TD with high sensitivity.

CONCLUSIONS The 360-degree turn test requires minimal time to administer and may be useful in mild-moderate PD for distinguishing PIGD from TD subtypes.