The predominance of extra-muscular manifestations (such as rash, arthralgia or severe respiratory impairment) as well as the low frequency of muscular signs in dermatomyositis with anti-MDA5 antibody (anti-MDA5 +) has led a consortium of French clinicians to question the term specific myositis antibody for the anti-MDA5 antibody, as well as the homogeneity of the disease.
In order to characterize the anti-MDA5 + phenotype, the authors performed an unsupervised analysis of anti-MDA5 + patients (n = 83/121) and compared the results to a group of control patients with myositis without anti-MDA5 antibodies (anti-MDA5 + MDA5-; n = 190/201) based on selected variables, collected retrospectively, without any missing data.
Clinicians have identified 3 subgroups among anti-MDA5 + patients:
- the first group (18.1%) corresponded to patients with severe respiratory disease with rapid progression and a very high mortality rate
- the second group (55.4%) corresponded to patients with pure dermato-rheumatological symptoms and a good prognosis
- the third corresponded to patients, mostly male, with severe cutaneous vasculopathy, frequent signs of myositis, and an intermediate prognosis
The unsupervised analysis nevertheless confirmed that the anti-MDA5 antibody delimits an independent group of patients, distinct from the anti-MDA5 patients with myositis.
The authors conclude that anti-MDA5 + patients have a distinct systemic syndrome from other patients with myositis and that there are three different prognosis subgroups.
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]