[Eosinophilic fasciitis: From pathophysiology to therapeutics].

Eosinophilic fasciitis (EF) is a rare connective tissue disorder characterized by painful edema and induration of the limbs and trunk, likely associated with hypereosinophilia and hypergammaglobulinemia. EF causes arthralgia and range of motion limitation, leading to significant functional impairment and poor quality of life. Since its description by Shulman in 1974, over 300 cases have been reported. We present here a review of the latest diagnostic, pathophysiological and therapeutic developments in this disease. Magnetic resonance imaging appears useful to guide diagnosis and biopsy. Diagnosis is based on a deep skin biopsy involving the fascia, which will reveal edema, sclerofibrosis of the muscular fascia and subcutaneous tissue, and an inflammatory infiltrate sometimes composed of eosinophilic polynuclear cells. EF may occur in patients treated with immune checkpoint inhibitors and the diagnosis should be raised in case of cutaneous sclerosis in these patients. The pathophysiology of the disease remains poorly understood, and its management lacks randomized, controlled, blinded trials. First-line treatment consists in oral corticosteroid therapy, sometimes combined with an immunosuppressant, mainly methotrexate. A better understanding of the pathophysiology has opened new therapeutic perspectives and clarified the role of targeted therapies in the management of EF, such as interleukin-6 inhibitors, whose efficacy has been reported in several cases.