Refractory serum immunoglobulin M elevation during anti‐interleukin (IL)‐1‐ or IL‐6‐targeted treatment in four patients with Schnitzler syndrome

Schnitzler syndrome is characterized by chronic urticarial rash, neutrophilic dermal infiltrate, recurrent fever, bone pain, elevated C‐reactive protein, and neutrophilic leukocytosis. The pathophysiology of Schnitzler syndrome is unknown, but it is considered to be an acquired form of an autoinflammatory disease because of the resemblance to clinical phenotypes of cryopyrin‐associated periodic syndrome, in which a gain‐of‐function mutation in NLRP3 causes overexpression of interleukin (IL)‐1β. Schnitzler syndrome is generally accompanied by a monoclonal immunoglobulin (Ig)M gammopathy with a long‐term risk of lymphoproliferation that is possibly associated with an MYD88 mutation. Herein, we present the following four patients with Schnitzler syndrome: a 63‐year‐old woman; a 65‐year‐old man; a 43‐year‐old woman; and a 63‐year‐old woman. Each patient fulfilled the Strasbourg diagnostic criteria, but none of the patients had any mutation in NLRP3 or MYD88 detected in their peripheral blood. Although approved treatment options for Schnitzler syndrome are lacking, our patients were treated with IL‐1‐targeted therapy (anakinra or canakinumab) or anti‐IL‐6 (tocilizumab). The acute inflammatory clinical manifestations improved completely with canakinumab and partially with anakinra and tocilizumab, but the serum IgM levels were gradually increased in all patients, even during treatment. To determine whether treatment with anti‐IL‐1β or IL‐6 prevents conversion to a hematopoietic disorder, further collection of cases and long‐term follow‐up will be needed.