Abstract
Manual muscle testing (MMT) and hand-held dynamometry (HHD) are commonly used in people with inflammatory myopathy (IM), but their clinimetric properties have not yet been sufficiently studied. To evaluate the reliability and validity of MMT and HHD, maximum isometric strength was measured in eight muscle groups across three measurement events. To evaluate reliability of HHD, intra-class correlation coefficients (ICC), the standard error of measurements (SEM) and smallest detectable changes (SDC) were calculated. To measure reliability of MMT linear Cohen`s Kappa was computed for single muscle groups and ICC for total score. Additionally, correlations between MMT8 and HHD were evaluated with Spearman Correlation Coefficients. Fifty people with myositis (56±14 years, 76% female) were included in the study. Intra-and interrater reliability of HHD yielded excellent ICCs (0.75–0.97) for all muscle groups, except for interrater reliability of ankle extension (0.61). The corresponding SEMs% ranged from 8 to 28% and the SDCs% from 23 to 65%. MMT8 total score revealed excellent intra-and interrater reliability (ICC>0.9). Intrarater reliability of single muscle groups was substantial for shoulder and hip abduction, elbow and neck flexion, and hip extension (0.64–0.69); moderate for wrist (0.53) and knee extension (0.49) and fair for ankle extension (0.35). Interrater reliability was moderate for neck flexion (0.54) and hip abduction (0.44); fair for shoulder abduction, elbow flexion, wrist and ankle extension (0.20–0.33); and slight for knee extension (0.08). Correlations between the two tests were low for wrist, knee, ankle, and hip extension; moderate for elbow flexion, neck flexion and hip abduction; and good for shoulder abduction. In conclusion, the MMT8 total score is a reliable assessment to consider general muscle weakness in people with myositis but not for single muscle groups. In contrast, our results confirm that HHD can be recommended to evaluate strength of single muscle groups.
Highlights
Inflammatory myopathies (IMs), including dermatomyositis (DM), polymyositis (PM) and associated myopathies, are systemic rheumatic muscle diseases characterized by chronic muscle inflammation [1]
Hip abduction and neck flexion had fair to good intrarater reliability
Interrater reliability was excellent for three muscle groups and fair to good for the other five muscle groups
Summary
Inflammatory myopathies (IMs), including dermatomyositis (DM), polymyositis (PM) and associated myopathies, are systemic rheumatic muscle diseases characterized by chronic muscle inflammation [1]. With a worldwide average annual incidence rate ranging from 0.2 to 8 in 100‘0000, IMs are relatively rare. The burden of the disease for affected patients is considerable. The weakness is symmetrical, proximal extremity muscles appear to be more affected, and neck flexors are weaker than extensors [4]. As a consequence of muscle weakness, people with myositis often report difficulties with activities of daily living, e.g., getting up from a chair, going up- or down the stairs, getting into a car, stepping onto a curb, lifting objects, washing hair, brushing teeth, and gripping objects [1, 2]
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