Session Type: ACR Poster Session C
Session Time: 9:00AM-11:00AM
Background/Purpose: Anti-Mi2 autoantibodies (Aabs) have been proposed to be highly specific for dermatomyositis (DM) and to be associated with a DM classical phenotype consisting of typical skin rashes and low extra-muscular features. Cancer has been estimated in about 30% of all DM patients. Patients with anti-Mi2 DM are considered having a good prognosis, possibly related to a markedly lower risk of malignancy reported in this subset. Nonetheless, there has been only a few and small cohort descriptions of this DM subgroup. Our objective was therefore to describe the phenotype of anti-Mi-2 DM in a large French cohort.
Methods: A national multicenter retrospective cohort study was performed (15 medical centers) including all patients with a clinical phenotype suggestive of DM (cutaneous manifestations and/or muscle involvement) and a positive anti-Mi2 Aabs. Medical records were retrospectively reviewed. Muscle strength was assessed using the Medical Research Council (MRC) scale and cancer-associated myositis (CAM) was defined as a cancer occurring ± 3 years of diagnosing myositis.
Results: A total of 65 patients were identified, 62% were female and mean age at diagnosis was 54 years old (yo) (±17 yo). DM skin rash was reported in 88% of patients, most frequently Gottron papules and/or sign (68%), periungueal erythema (51%) and heliotrope rash (40%). Peripheral muscle weakness was reported in 92% of patients and dysphagia was reported in 34% of patients. At diagnosis, patients displayed severe muscle weakness (MRC 3/5, ±1/5) with mean CK level of 5085 UI/L (±5535 UI/L). Systematic review of muscle biopsies (n=11) showed marked inflammatory infiltrates. Strikingly, necrosis and regeneration were identified in all patients (n=11/11). C5b-9 deposition was found in all patients mainly on non-necrotic fibers but only sparsely on capillaries and without prominent capillary loss. Arthritis, Raynaud phenomenon and interstitial lung disease were reported in less than 20 % of patients. CAM was identified in 20% of patients and detected within one year and a half of DM diagnosis in most patients (n=11/12). All CAM patients, but one (38 yo), were diagnosed over 50 yo. There was no predominant histological subtype of malignancy (gastro-intestinal, urological, gynecological and pulmonary) and cancer was metastatic in a third of patients. Survival rate was 83% after a mean follow-up of 4.9 years from cancer diagnosis. Ninety-eight percent of patients were initially treated with corticosteroids (CS), in combination with immunosuppressant (IS) in 60% of cases. Patients treated with CS monotherapy (n=14), needed second-line agents upon follow-up in 60% of cases. In all, 53% of patients relapsed upon CS and/or IS tapering.
Conclusion: In this large French cohort, patients with anti-Mi2 DM displayed a phenotype with 3 main characteristics (i) pure DM phenotype (low overlap features) (ii) necrotizing myositis (severe weakness, high CK level and muscle fiber necrosis) and (iii) higher than expected malignancy rate.
To cite this abstract in AMA style:Landon-Cardinal O, Monseau G, Schoindre Y, Rigolet A, Champtiaux N, Hervier B, Masseau A, Hachulla E, Papo T, Terrier B, Meyer A, Kahn JE, Maurier F, Gaches F, Salort-Campana E, Zenone T, Costedoat-Chalumeau N, Perez F, Samson M, Piette AM, Moulis G, Audia S, Genot S, Schleinitz N, Lefevre G, Verneuil L, Benveniste O, Allenbach Y, Bienvenu B. Anti-Mi2 Dermatomyositis Revisited: Pure DM Phenotype with Muscle Fiber Necrosis and High Risk of Malignancy [abstract]. Arthritis Rheumatol. 2016; 68 (suppl 10). https://acrabstracts.org/abstract/anti-mi2-dermatomyositis-revisited-pure-dm-phenotype-with-muscle-fiber-necrosis-and-high-risk-of-malignancy/. Accessed June 21, 2021.
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ACR Meeting Abstracts - https://acrabstracts.org/abstract/anti-mi2-dermatomyositis-revisited-pure-dm-phenotype-with-muscle-fiber-necrosis-and-high-risk-of-malignancy/