Background/Purpose: Muscle weakness is often progressive and persistent in Juvenile Dermatomyositis (JDM). Muscle strength testing is useful for evaluating severity of muscle weakness. There is age limitation for testing muscle strength; the Manual Muscle Test (MMT) and the Childhood Myositis Assessment Scale (CMAS) were selected as myositis core set of outcome measures in adults and children (Miller FW Rheumatology 2001, 40:1262) (Ruperto N Rheumatology 2003, 42: 1452). Both tests were carried out according to the Brazilian Registry of JDM protocol. Muscle strength scored by MMT and CMAS in newly diagnosed JDMwas compared, at onset and follow up for 2 years .

Methods: All 96 patients selected in the JDM registry with diagnoses certified by the attending physician were elicited to perform the tests according to age and willing to participate, under supervision of a physician or physiotherapist; at baseline, 6, 12, 18 and 24 month follow up. The Manual Muscle Test (MMT) (Rider LG Arthritis Care Res 2010; 62:465) version was developed based on Kendall method using a summary of 8 muscle groups and a potential range of 0-80, being 1 axial, 5 proximal (2 upper extremity and 3 lower extremity) and 2 distal muscles (upper and lower extremity). Childhood Myositis Assessment Scale (CMAS) (Lovell DJ Arthritis Rheum 1999, 42: 2213-9) is composed by 14 manoeuvres testing proximal muscle strength and the version of 0 to 53 – final score was selected (Huber A Arthritis Care Res 2014, 66:648). Attending physicians were trained by a video performance (recorded by Dr R Rennebohn). The scores were compared by Poisson model and Wald test for repeated measures with significance set at 5% or p 0.05.

Results: The number (n) of performed tests was variable for each of the longitudinal assessments. MMT (mean± SD) scores were: Baseline (n=92) (37.5±34.6)*, 6m (n= 60) (58.5±29)*, 12m (n=44) (66.6±23.7), 18m (n= 26) (72.8±16.7) and 24m (n=17)(74.8±7.8), the difference among visits was significant with p=0.015*; and the only significant difference (Wald test) was from the baseline to six months. CMAS test scores had no significant variation between visits. The mean± SD scores of CMAS scores (0-53), were Baseline (n=60) (29.5±11.4), 6m (n=51) (32.3±11.4), 12m (n=41) (34.2±5.8), 18m (n=23) (34 ± 6) and 24 m (n=15) (33.3±5.4) p = 0.06 (NS).

Conclusion: We tested the feasibility and validity of MMT and CMAS performed by the attending physician or physiotherapist in a national JDM registry . Discontinued follow up was the main limitation. There was marked improvement in MMT scores during the first 6 months, compared to only mild improvement of CMAS, that persisted stable with moderate weakness indicating persistent functional impairment up to 2 years.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/the-brazilian-registry-of-juvenile-dermatomyositis-jdm-ii-a-longitudinal-assessment-of-muscle-strength-by-manual-muscle-test-mmt-and-childhood-myositis-assessment-scale-cmas-tools/