A patient with urticarial lesions, recurrent fever, and IgM-type monoclonal gammopathy.

Schnitzler syndrome is a rare acquired autoinflammatory syndrome. It presents with an urticarial rash and a monoclonal gammopathy, usually of the IgM kappa type. In addition, patients can present with bone and/or joint pain, recurrent fever, asthenia, weight loss, myalgia, headache, lymphadenopathy, hepatomegaly, or splenomegaly. An elevation of blood inflammation markers is commonly found. Skin biopsy of the urticarial rash reveals neutrophilic infiltrate, known as neutrophilic urticarial dermatosis. To confirm the diagnosis, two sets of diagnostic criteria have been established. The syndrome shares many features with other autoinflammatory disorders, such as adult-onset Still's disease and NLRP3-auto-inflammatory disorders (NLRP3-AID, formerly known as cryopyrin-associated periodic syndromes, or CAPS). The pathogenesis of the disease is not yet fully understood; however, it is believed that interleukin (IL)-1β plays a crucial role and explains the excellent effectiveness of IL-1 blocking agents. It is a chronic disease, and some patients develop lymphoproliferative disease, and seldom AA amyloidosis.