[Severe MDA5 dermatomyositis associated with cancer and controlled by JAK inhibitor].

Dermatomyositis is an idiopathic inflammatory myopathy with various clinical and serological profiles, including poor prognosis forms for which aggressive immunosuppressive treatment is warranted. We report the case of a 60-year-old woman referred to our hospital for an anti-melanoma differentiation-associated 5 gene antibody-positive dermatomyositis (MDA5 DM) with rapidly progressive interstitial pneumonia, typical cutaneous features and muscular impairment. Treatment with high-dose methylprednisolone, cyclophosphamide and gamma globulin was performed, but the patient remained corticodependant. Blood detection of positive interferon signature justified the administration of an anti-JAK1/2, leading to the clinical remission and the regression of the interferon signature. After 12 months of follow up, a small cell carcinoma was discovered, raising the question of a paraneoplastic syndrome, for which the most recent datas are quite reassuring for this kind of MDA5 DM. The presentation of this case is of twofold interest: describing one of the first report of successful treatment of intereronopathy MDA5 DM with ruxolitinib and highlighting an association with a cancer, which is not expected for this phenotype of dermatomyositis.