Development of an activity scale for individuals with advanced Parkinson disease: Reliability and "on-off" variability

Background and Purpose. Functional mobility in people with advanced Parkins on disease, some of whom have a variable response to drug treatment, is oft en difficult to evaluate. The objectives of this study were to investigate the interrater reliability of measurements obtained with a scale designed t o measure mobility and to determine the impact of self-rated dyskinesias an d fluctuations on the measure. Subjects. Twenty-nine people with Parkinson disease and with disability and considerable disease duration ((X) over bar =11.7 years, SD=4.9, range=6-22) took part in the study. Methods. The subj ects' performance on a 10-item scale was videotaped. The videotapes were th en scored by 2 independent raters, and the scores were used to determine in terrater reliability. The stability of 6 repeated measurements was examined in the home situation, taking into account self-rated fluctuations of moto r performance. Results. Weighted Kappa values of agreement (.86-.98) confir med the reliability between testers. Measurement during the "on" phase (whe n medication was working optimally) and the "off" phase (when the action of medication was strongly decreased or absent) led to different measurements . Measuring frequently within "on" and "off" phases gave relatively stable measurements for total function, bed transfers, and gait akinesia, the latt er during the "off' phase only (intraclass correlation coefficients [ICCs] =.70-.93). However, more modest repeatability applied to transfers from a c hair (ICC=.65-.67). Conclusion and Discussion. To ensure valid results in f uture effect studies, clinical differentiation between "on" and "off' phase measurements is proposed on the basis of patients' own perception of their medication status.