How to identify tremor dominant and postural instability/gait difficulty groups with the movement disorder society unified Parkinson's disease rating scale: Comparison with the unified Parkinson's disease rating scale

Background Formulas were developed to define tremor dominant (TD) and postural instability/gait difficulty (PIGD) phenotypes of Parkinson's Disease (PD) using the Movement Disorder Society Unified Parkinson's Disease Rating Scale (MDS‐UPDRS). TD and PIGD designations, based on the original Unified Parkinson's Disease Rating Scale (UPDRS), provided useful designations for classifying different phenotypes of PD. With the advent of the MDS‐UPDRS, a valid set of calculations for these phenotypes is needed. Methods UPDRS and MDS‐UPDRS scores were collected on 877 PD patients. TD/PIGD scores were calculated using the UPDRS formula for all patients. Comparable TD and PIGD items from the MDS‐UPDRS were used to calculate new ratios. Data were analyzed using receiver operating characteristic models. Results The new MDS‐UPDRS TD/PIGD ratios accounted for a significant area under the curve compared with the UPDRS classification. Optimal sensitivity and specificity were obtained with MDS‐UPDRS cutoff scores of ≥1.15 for TD classification and ≤0.90 for PIGD. Conclusions The development of comparable and valid PIGD and TD scores from the MDS‐UPDRS provides a clear method for clinicians and researchers to transition from the original UPDRS to the new MDS‐UPDRS in categorizing patients with different clinical phenotypes. © 2013 Movement Disorder Society