Parkinson's disease: quantification of disability based on the Unified Parkinson's Disease Rating Scale

To develop a simple measure for quantification of the disability (dependency) due to Parkinson's disease (PD).

65 nondemented PD outpatients, stage 1 to 5 of the Hoehn and Yahr Classification (HY).

HY, Schwab and England Scale, Northwestern University Disability Scale, Columbia University Rating Scale, Webster Scale, Barthel's Index, finger tapping, and timed "Up & Go" test. Six items from the ADL Section of the Unified PD Rating Scale (UPDRS)--as representative of the most basic ADL--were chosen to compose the UPDRS disability score (UDS), that was simultaneously rated by three observers. Global evaluations of disability by patient and physician were also recorded.

Descriptive, Cronbach alpha, kappa of Fleiss, Spearman rank correlation coefficients, Kruskal-Wallis test, and factor analysis.

Internal consistency (Cronbach alpha = 0.86-0.87) and interobserver reliability (kappa = 0.84-0.98) were satisfactory. Convergent validity of the UDS with the applied PD rating scales (R = 0.76-0.92), global evaluations (R = 0.84-0.88), and timed tests (R = 0.47-0.65) was highly significant (all, p < 0.001). Distribution of UDS values across the HY categories showed significant trends (Kruskal-Wallis test, p < 0.001). A single factor explaining over 64% of the variance was identified.

A simple and valid instrument for standardized evaluation of disability in PD is embedded in the UPDRS.