Identified in 2009, the anti-MDA5 autoantibodies are considered to be specific for dermatomyositis, a rare autoimmune disease which can cause skin, muscle and / or lung damage (interstitial lung disease). A large observational study conducted between 2011 and 2017 in 37 French hospitals included 83 patients with anti-MDA5 autoantibodies, compared to 190 patients with myositis without anti-MDA5 followed at the Pitié-Salpêtrière hospital (Paris) . Its results confirm that anti-MDA5 patients form a distinct group, itself composed of 3 subsets of different prognoses as shown for the first time in this study:
- the first subgroup, well known, brings together 18.1% of patients and is characterized by severe interstitial pneumonitis rapidly progressive and a very high mortality rate;
- the second (55.4%) combines dermatological and rheumatic symptoms (82.6% of arthralgia) and proves to have a good prognosis;
- the third subgroup (26.5%) is rather male (72.7% of patients), with severe cutaneous vasculopathy (Raynaud’s phenomenon, ulcers, calcinosis, etc.), frequent signs of myositis (weakness of the proximal muscles in 68.2% of cases) and an intermediate prognosis.
Gender, the existence of a Raynaud’s phenomenon and the presence of joint pain or arthritis allow prediction of membership of this or that subgroup in 83.3% of cases.
According to the authors of the publication, dermatomyositis with anti-MDA5 is more a systemic syndrome than a musculo-cutaneous disease. Anti-MDA5 autoantibodies should be sought in the case of seronegative arthritis, interstitial lung disease with suspected autoimmune character or, in intensive care, before an acute respiratory distress syndrome of unknown origin.
Different phenotypes in dermatomyositis associated with anti-MDA5 antibody: Study of 121 cases. Allenbach Y, Uzunhan Y, Toquet S, Leroux G, Gallay L, Marquet A, Meyer A, Guillaud C, Limal N, Gagnadoux F, Hervier B, Borie R, Deligny C, Terrier B, Berezne A, Audia S, Champtiaux N, Devilliers H, Voermans N, Diot E, Servettaz A, Marhadour T, Castelain V, Humbert S, Blanchard-Delaunay C, Tieulie N, Charles P, Gerin M, Mekinian A, Priou P, Meurice JC, Tazi A, Cottin V, Miyara M, Grange B, Israël-Biet D, Phin-Huynh S, Bron C, De Saint Martin L, Fabien N, Mariampillai K, Nunes H, Benveniste O; French Myositis Network. Neurology. 2020 Jun 2. pii: 10.1212/WNL.0000000000009727. doi: 10.1212/WNL.0000000000009727. [Epub ahead of print]