How reproducible is home-based 24-hour ambulatory monitoring of motor activity in patients with multiple sclerosis?

OBJECTIVE To determine the reproducibility of 24-hour monitoring of motor activity in patients with multiple sclerosis (MS). DESIGN Test-retest design; 6 research assistants visited the participants twice within 1 week in the home situation. SETTING General community. PARTICIPANTS A convenience sample of ambulatory patients (N=43; mean age ± SD, 48.7±7.0y; 30 women; median Expanded Disability Status Scale scores, 3.5; interquartile range, 2.5) were recruited from the outpatient clinic of a university medical center. INTERVENTIONS Not applicable. MAIN OUTCOME MEASURES Dynamic activity and static activity parameters were recorded by using a portable data logger and classified continuously for 24 hours. Reproducibility was determined by calculating intraclass correlation coefficients (ICCs) for test-retest reliability and by applying the Bland-Altman method for agreement between the 2 measurements. The smallest detectable change (SDC) was calculated based on the standard error of measurement. RESULTS Test-retest reliability expressed by the ICC(agreement) was .72 for dynamic activity, .74 for transitions, .77 for walking, .71 for static activity, .67 for sitting, .62 for standing, and .55 for lying. Bland and Altman analysis indicated no systematic differences between the first and second assessment for dynamic and static activity. Measurement error expressed by the SDC was 1.23 for dynamic activity, 66 for transitions, .99 for walking, 1.52 for static activity, 4.68 for lying, 3.95 for sitting, and 3.34 for standing. CONCLUSIONS The current study shows that with 24-hour monitoring, a reproducible estimate of physical activity can be obtained in ambulatory patients with MS.