Functional index‐2: Validity and reliability of a disease‐specific measure of impairment in patients with polymyositis and dermatomyositis

Abstract

Objective. To revise the content of the Functional Index in myositis (FI) and to evaluate measurement properties of a revised FI. Methods. Previously performed FI (n ‫؍‬ 287) were analyzed for internal redundancy and consistency, and ceiling and floor effects. Content was evaluated and a preliminary revised FI was developed. To evaluate the construct validity of the preliminary revised FI, it was compared with isokinetic measurements of muscular strength and endurance, the Myositis Activities Profile, disease impact on general wellbeing, and creatine phosphokinase levels. Minor adjustments were made and the revised FI was investigated for interrater reliability and intrarater reliability over a 1-week period. After this, some minor, additional adjustments were made leading to the final version, FI-2. Results. Five tasks were removed from the original FI due to ceiling effects. Performance pace and number of repetitions were modified for the remaining tasks. A moderate correlation (r s ‫؍‬ 0.58) was found between the shoulder flexion task of the preliminary revised FI and isokinetic measurements of shoulder flexion endurance. Intraclass correlation coefficient (ICC) for interrater reliability of the revised FI varied from 0.86 -0.99 with no systematic differences. ICC for intrarater reliability varied from 0.56 -0.99 with systematic differences (P < 0.05) between test and retest in 3 of the tasks. The sit-up task was excluded due to low intrarater reliability resulting in the final 7-item FI-2. There was a good correlation between tasks on the right and left side suggesting that the FI-2 could be performed unilaterally. Conclusion. The FI-2 is a valid and reliable outcome measure of impairment for patients with polymyositis or dermatomyositis. It is well tolerated and the unilateral FI-2 requires a maximum of 20 minutes to perform. Further evaluation of sensitivity to change and testing in healthy individuals needs to be conducted.

Assessing Function and Endurance in Adults with Spinal and Bulbar Muscular Atrophy: Validity of the Adult Myopathy Assessment Tool

“…However, the data suggesting that the sit-up was the most difficult task was unexpected and has not been previously described in SBMA. Trunk weakness is a notable finding that has been observed in myopathies such as polymyositis and dermatomyositis [51]. Muscle groups of the extremities are typically more readily tested with dynamometry than trunk muscles, so the trunk musculature is typically omitted from objective strength assessment studies.…”

Abatacept in the treatment of adult dermatomyositis and polymyositis: a randomised, phase IIb treatment delayed-start trial

“…Concomitant methotrexate or azathioprine was allowed, with stable doses for ≥1 month prior to inclusion in the study. Active disease was defined as persisting or worsening muscle weakness (Manual Muscle Test (MMT)-8 bilaterally <150) or low endurance measured by Functional Index for myositis (FI-2) <20% of upper value,15 together with at least one other sign of active disease: elevated (above upper limit of normal) serum levels of muscle enzymes, inflammation in a recent muscle biopsy (<1 month) or on MRI findings consistent with inflammation, or active extramuscular disease. Inclusion and exclusion criteria are shown in online supplementary material 1 and 2).…”

Does Computed Tomography–Based Muscle Density Predict Muscle Function and Health‐Related Quality of Life in Patients With Idiopathic Inflammatory Myopathies?

“…Participants underwent manual muscle testing (MMT-8) and muscle endurance testing using the Functional Index-2 (FI-2) (16). Frequency, intensity, type, and duration of weekly exercise were assessed using the International Physical Activity Questionnaire (IPAQ) (17).…”