Résumé :
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Inclusion body myositis (IBM) is a late-onset inflammatory myopathy which is the most common occurring over the age of 50 years. New emerging treatments are being to be tested in a near future and the choice of robust and reliable outcome measures is needed for efficacy assessment. Few natural history studies have been carried out on this rare, slowly progressive disorder presenting a large phenotypic variability. In the present study, we intended to follow 22 patients suffering from an IBM during 9 months to determine over this period of time the most sensitive outcome measures among several assessment methods: 6-minute walk test (6MWT), strength dynamometry of hand grip and elbow, wrist, ankle and knee extension and flexion, manual muscle testing and clinical scores (Barringazzini, Walton, Karnofsky, RMI score /15, IBM score /100).Twenty two patients (14 women and 8 men) were included in the study; 16 (9 women and 7 men) were reassessed about 9 months later. Results show very large between-individual variability in the impairments. No correlations were found between the duration of the disease and strength, except for knee extension. For the upper limb, the non dominant side was more affected than the dominant side. The most affected muscle functions were from worst to most preserved: knee extension, ankle flexion, hand grip, wrist flexion, elbow flexion. After 9 months, no significant changes occurred in strength, 6MWT or clinical scores. The composite strength score showed a mean decrease of 1.4 % only. This result is in contrast with previous works which revealed larger decrease in strength.This study underlines the difficulty in choosing reliable outcome measures when the patient deterioration is progressive, slow and variable among individuals.
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