Schnitzler Syndrome at 50: What We’ve Learned So Far

First described by Liliane Schnitzler in 1972, Schnitzler syndrome (SchS) has evolved from a rare association of chronic urticarial rash and IgM monoclonal gammopathy into a well-defined acquired autoinflammatory disorder with systemic features—recurrent fever, arthralgia, bone pain, and elevated acute-phase reactants. A major conceptual shift came in the mid-2000s with recognition of overlap with cryopyrin-associated periodic syndromes (CAPS). The pivotal finding was that IL-1 blockade, particularly with anakinra, produced rapid, often complete symptom resolution—establishing IL-1β–mediated inflammation as central and reclassifying SchS as an innate immune disorder. Phenotypic similarity to CAPS prompted searches for NLRP3 mutations. Although isolated somatic mosaicism was reported, larger studies found no consistent mutations in classical SchS; many positive cases are now reclassified as late-onset CAPS. Current evidence supports NLRP3 inflammasome overactivation and excess IL-1β as downstream mechanisms, though the upstream trigger remains unknown. Attention has more recently turned to the clonal hematopoiesis associated with SchS. Somatic MYD88 L265P mutations, characteristic of Waldenström macroglobulinemia, occur in a subset of patients and might represent a plausible bridge (via NF-κB activation) between gammopathy and innate immune activation. Recently described “Schnitzler-like” syndromes, which lack monoclonal gammopathy but demonstrate other SchS traits, including IL-1 responsiveness, have prompted reconsideration of the SchS diagnostic criteria. Therapeutically, IL-1 inhibitors (e.g., anakinra, canakinumab) are now standard of care, inducing sustained remission and reducing AA amyloidosis risk, though they neither eliminate the paraprotein nor prevent lymphoproliferative progression. Clone-directed strategies—Bruton tyrosine kinase inhibitors and plasma cell–targeted agents—are under investigation. The fundamental relationship between monoclonal gammopathy and inflammasome activation remains unresolved, and clarifying it may enable a shift from cytokine suppression toward disease-modifying or curative approaches.