Development and testing of a hybrid measure of muscle strength in juvenile dermatomyositis for use in routine care

Giulia Camilla Varnier, Silvia Rosina, Cristina Ferrari, Angela Pistorio, Alessandro Consolaro, Francesca Bovis, Sara Dalprà, Clarissa Pilkington, Susan Maillard, Adele Civino, Elena Tsitsami, Jaime de Inocencio, Marija Jelusic, Jelena Vojinovic, Graciela Espada, Balahan Makay, Maria Martha Katsicas, Polixeni Pratsidou-Gertsi, Dragana Lazarevic, Anand Prahalad RaoDenise Pires Marafon, Nicolino Ruperto, Alberto Martini, Angelo Ravelli

Research output: Contribution to journalArticlepeer-review


OBJECTIVE: To develop and test a hybrid measure of muscle strength for juvenile dermatomyositis (JDM), which is based on the combination of the Manual Muscle Testing 8 (MMT8) and the Childhood Myositis Assessment Scale (CMAS), but is more comprehensive than the former and more feasible than the latter.

METHODS: The hybrid MMT/CMAS (hMC) is composed of all 8 items of the MMT8 and 3 items of the CMAS: 1) time of head lift; 2) assessment of abdominal muscles; 3) floor rise. The score ranges from 0 to 100, with 100 indicating normal muscle strength. Validation procedures were conducted using three large multinational patient samples including a total of 810 JDM patients.

RESULTS: The hMC revealed face and content validity, good construct validity, excellent test-retest reliability (intraclass correlation coefficient = 0.99) and internal consistency (Chronbach's alpha = 0.94), strong responsiveness to clinical change over time (standardized response mean = 0.8 among patients judged as improved by the caring physician), and satisfactory capacity to discriminate patients judged as being in the states of inactive disease or low, moderate, or high disease activity by the physician (p < 0.001) or patients whose parents were satisfied or not satisfied with illness course (p < 0.001).

CONCLUSION: The hMC was found to possess good measurement properties in a large population of patients with a wide range of disease activity and severity. The new tool, which is primarily intended for use in routine clinical care, should be further tested in other populations of patients evaluated prospectively. This article is protected by copyright. All rights reserved.

Original languageEnglish
JournalArthritis care and research : the official journal of the Arthritis Health Professions Association
Publication statusE-pub ahead of print - Dec 15 2017


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