LAUSR

Myositis are systemic autoimmune rare diseases characterized by muscle inflammation and weakness. Even though the signs of active disease have been resolved, myositis patients frequently present residual muscle weakness, decreased physical performance and sustained disability. This condition has been coined on the term “damage” (as opposed to “activity”).Sarcopenia is a frequent, progressive and generalized skeletal muscle disorder characterized by low muscle strength and mass leading to handicap, decreased quality of life and increased mortality.1Prevalence and significance of sarcopenia in myositis patients has never been reported.To study sarcopenia in myositis patients with low or no disease activity.Adult myositis patients (2017 ACR/EULAR criteria), with disease duration greater than 12 months, creatine kinase serum level (CK) less than 500 U/l, stable medication for 6 months were enrolled. Patients with inclusion body myositis were excluded. Total (LM) and appendicular (ALM) muscle mass were measured using dual-energy X-ray absorptiometry (DXA, Hologic) and muscle grip strength was measured using Jamar dynamometer. Sarcopenia was defined according to the EWGSOP2 consensus.129 patients (20 female, 68.9%), with a median age of 61 years (50.5-71) were enrolled. They suffered from dermatomyositis (DM, n=4), immune-mediated necrotizing myopathy (IMNM), n=8), anti-synthetase syndrome (ASS, n=9), scleromyositis (SM, n=8) since 4.7 years (2.8-8.3). At the evaluation, muscle strength assessed with MMT-8 was 139/150 (136-147), MMT-12 was 210/220 (204-216) and CK were 131.5 U/l (105.5-202). Four patients (13.8%) were sarcopenic. Sarcopenic patients were older (73.4 years (66.2-80.5) vs 58.7 years (44.2-79.6), p=0.03), with a longer disease duration (7.3 years (5.3-11.8) vs 4.3 (2.7-8.3), p = 0.1), longer time with increased CK (449 days (169.8-954) vs 255.5 (124-872.8)), higher maximum CK values (6000 U/l (2205-7000) vs 1636 (900-4457)). They suffered from IMNM (2/4, 50%); DM (n=1) and SM (n=1), had more frequently disease-related cardiac involvement (50% vs 4%, p=0.04), and tended to a longer steroid therapy duration (2.4 years (0.8-5) vs 1.8 (1.3-3.9), p=0.9) and a higher number of immunomodulatory drugs (2.5 (2-5.3) vs 2 (2-3), p=0.3).At the evaluation, sarcopenic patients were globally weaker as highlighted by lower MMT-12 (201 (196.8-206.8) vs 213 (207-217.5), p=0.02). Head flexo-extensors and proximal upper muscles were especially weaker (respectively, p=0.04 and p=0.03). Muscle performance was also lower in sarcopenic patients as assessed by distance covered at 6-minute walk test (6mWT, p=0.003) and number of squats in 30 seconds (p=0.005). Time to drink a glass of water was significantly longer in sarcopenics (p=0.04) even if any patient referred dysphagia. Health assessment questionnaire score was greater (1.4 (0.8-2) vs 0.6 (0.2-1), p=0.04) indicating higher handicap. LM positively correlated with MMT-8 (ρ=0.5, p=0.01) and MMT-12 (ρ=0.5, p=0.004), with number of squats in 30 seconds (ρ=0.7, p=0.0003) and 6mWT distance covered/lower limit (ρ= 0.5, p=0.01). Moreover, LM negatively correlated with time to drink a glass of water (ρ=-0.6, p=0.002).Muscle mass measured by DXA is a relevant parameter for muscle damage and disability in myositis patients. Sarcopenic myositis patients represent a subgroup with important muscle damage and handicap.[1]Cruz-Jentoft AJ et al. Sarcopenia: revised European consensus on definition and diagnosis. Age Ageing. 1 Jan 2019;48(1):16-31.None declared