Measurement of Health-Related Quality of Life in Patients With Amyotrophic Lateral Sclerosis in Clinical Trials of New Therapies

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Abstract
Recent trials of amyotrophic lateral sclerosis (ALS) therapies have included the Sickness Impact Profile (SIP) to evaluate health-related quality of life (HQL). The purpose of this study was to assess the feasibility, psychometric properties, and interpretation of the Sickness Impact Profile in this setting. The Sickness Impact Profile was administered at baseline, 3, 6, and 9 months during a double-blind, placebo-controlled study of recombinant human insulin-like growth factor I. The frequency of missing Sickness Impact Profile data and administration time were recorded. Patients' scores on the Appel ALS (AALS) Rating Scale were used to identify a stable subgroup for reliability testing and clinically distinct groups for validity testing. Internal consistency reliability and reproducibility were evaluated using Cronbach's alpha and intraclass correlation coefficients, respectively. Analysis of variance (ANOVA) models and t tests were used to assess validity. Effect sizes and the responsiveness index were used to assess responsiveness. At baseline, 259 (97%) patients completed a 30-minute Sickness Impact Profile interview. At subsequent assessments, response rates ranged from 92% to 97% and mean administration times ranged from 25 to 27 minutes. The overall Sickness Impact Profile score demonstrated alpha reliability and 3-month stability coefficients of 0.94 and 0.80, respectively. Baseline overall Sickness Impact Profile scores discriminated between patients in the two AALS-defined groups with a mean of 13.0 ± 7.8 and 24.0 ± 11.7 in the better and worse AALS groups, respectively. Similarly, mean overall SIP change scores discriminated patients progressing at different rates (slow to moderate = 4.00 ± 7.97; rapid = 10.74 ± 8.76). With few exceptions, dimension and category scores met similar criteria. Responsiveness statistics for the physical and overall Sickness Impact Profile scores were lower at 3 months and higher at 6 and 9 months. The feasibility, psychometric, and interpretive findings support the validity of the Sickness Impact Profile for assessing outcomes of amyotrophic lateral sclerosis and its treatment. Based on these findings, we recommend including the Sickness Impact Profile in future amyotrophic lateral sclerosis clinical trials.