Schnitzler syndrome: an under-diagnosed clinical entity.

Schnitzler syndrome is considered to be a rare disorder characterized by a monoclonal IgM protein and chronic urticaria that is associated with considerable morbidity. We hypothesized that the syndrome may be under-recognized and patients may be deprived of highly effective therapy in the form of anakinra. We performed a retrospective search of the dysproteinemia database at Mayo Clinic as well as the medical records of all patients with chronic urticaria to determine the true incidence of the disease. We compared patients with the diagnosis of Schnitzler syndrome and those who met the criteria but in whom the syndrome was not recognized. Comparisons between groups were performed and survival curves determined. We identified 16 patients with diagnosed Schnitzler syndrome and an additional 46 patients who met diagnostic criteria. The monoclonal protein was IgMκ in 94% of patients. Therapy with anakinra in 4 patients led to rapid and complete resolution of symptoms. The median overall survival for this syndrome is over 12.8 years. Progression to lymphoma was only observed in 8% of patients; this is lower than previous reports. Schnitzler syndrome may be present in up to 1.5% of patients with a monoclonal IgM in their serum and likely under-recognized as a clinical syndrome.