The Schnitzler syndrome: chronic urticaria in disguise: a single-centre report of 11 cases and a critical reappraisal of the literature.

OBJECTIVES: The Schnitzler syndrome is a rare inflammatory disorder, with a chronic urticaria-like rash and an IgM (rarely IgG) monoclonal gammopathy as cardinal features. Interleukin-1 β is regarded as the key mediator and the interleukin-1 receptor antagonist anakinra has been proposed as first-line treatment. This case series of eleven patients is intended to enhance disease awareness and to compare our centre's experience with that of literature.

METHODS: We describe the clinical features and disease course of 11 patients with a definite Schnitzler syndrome, according to the Strasbourg diagnostic criteria, encountered in the University Hospital, Leuven, Belgium, between 1995 and 2015.

RESULTS: Eleven patients, with a median age of 55 years, were diagnosed with Schnitzler syndrome. All but one were diagnosed during the last decade. Of 6 patients treated with anakinra, 2 had a suboptimal response and 2 had poor tolerance (injection site reaction and neutropenia, respectively). Two of the 11 patients died as a consequence of the disease, culminating in Waldenström's macroglobulinaemia and AA amyloidosis, respectively.

CONCLUSIONS: The Schnitzler syndrome is rare, but probably underdiagnosed. In a patient with a chronic urticaria-like dermatosis, minor itch, intermittent fever and bone or joint aches, protein electrophoresis and immunofixation should be ordered. Especially, a finding of a monoclonal IgM kappa fits the diagnosis of Schnitzler syndrome. Anakinra may provide symptomatic relief, although the response is not always spectacular. The outcome is not always benign as fatal complications may occur.