The Schnitzler syndrome is a rare entity characterized by an urticarial rash and recurrent fever in a patient with a monoclonal IgM component. Other frequent signs include joint, bone and muscle pain, enlarged spleen, liver and lymph nodes, increased blood sedimentation rate (BSR), elevated neutrophil count and abnormalities on bone morphologic investigations. In 2001, the investigators proposed criteria to diagnose this syndrome, which are currently admitted in the literature. The main complications of the Schnitzler syndrome are a difficult-to-control inflammatory anemia, AA-amyloidosis and malignant B lymphoproliferative disorders. About 15% of patients with a Schnitzler will eventually develop a lymphoproliferative disorder; thus this syndrome allows studying the relationship between lymphomagenesis and inflammation. By many aspects, the Schnitzler syndrome is reminiscent of auto-inflammatory syndromes. Though the term auto-inflammatory disease is as to yet restricted to diseases with Mendelian inheritance, some polygenic inflammatory diseases like for example Crohn's disease clearly involve pathogenetic pathways shared with the monogenic auto-inflammatory syndromes. The investigators stipulate that this could also be the case in the Schnitzler syndrome for the following reasons: (1) this is a recurrent fever of unknown cause; (2) the peculiar eruption, characterized pathologically by a neutrophilic infiltrate very similar to the one observed in the auto-inflammatory cryopyrinopathies (CINCA/NOMID syndrome, Muckle-Wells syndrome and familial cold-urticaria); the investigators recently individualized this particular eruption, significantly associated with systemic inflammatory disease, within the group of neutrophilic urticarias (Kieffer et al. Medicine, in press); (3) the occurrence of aseptic neutrophilic osteitis, very similar to the one reported in patients with Majeed syndrome, another auto-inflammatory syndrome; (4) a significant increase of neutrophil count, not otherwise explained; (5) a spectacular response to the IL-1 inhibitor, within hours after the first injection, similar to what is reported in the PAPA (pyogenic arthritis, pyoderma gangrenosum and acne) syndrome or the cryopyrinopathies, suggesting a direct pathogenic effect of IL-1.
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