Schnitzler Syndrome

The Schnitzler syndrome is a rare and underdiagnosed entity which is considered today as being a paradigm of an acquired/late onset auto-inflammatory disease. It associates a chronic urticarial skin rash, corresponding from the clinico-pathological viewpoint to a neutrophilic urticarial dermatosis, a monoclonal IgM component and at least 2 of the following signs: fever, joint and/or bone pain, enlarged lymph nodes, spleen and/or liver, increased ESR, increased neutrophil count, abnormal bone imaging findings. It is a chronic disease with only one known case of spontaneous remission. Except of the severe alteration of quality of life related mainly to the rash, fever and pain, complications include severe inflammatory anemia and AA amyloidosis. About 20% of patients will develop a lymphoproliferative disorder, mainly Waldenström disease and lymphoma, a percentage close to other patients with IgM MGUS. It was exceedingly difficult to treat patients with this syndrome until the IL-1 receptor antagonist anakinra became available. Anakinra allows a complete control of all signs within hours after the first injection, but patients need continuous treatment with daily injections.In many aspects, the Schnitzler syndrome resembles the genetically determined auto-inflammatory syndromes involving activating mutations of the NLRP3 inflammasome. This latter point and its consequences will be addressed.

Schnitzler's syndrome is a rare autoinflammatory disorder characterized by interleukin-1ß-mediated and neutrophil-dominated inflammation. Neutrophil extracellular traps (NETs) are web-like structures of decondensed chromatin, histones, and antimicrobial peptides released by neutrophils. NETs were initially described in the context of pathogen defense but are also involved in autoimmune-mediated skin diseases. Here, we assessed the role of neutrophil extracellular trap formation (NETosis) in Schnitzler's syndrome. Immunofluorescence co-staining of myeloperoxidase and subnucleosomal complex was performed on lesional skin samples from patients with Schnitzler's syndrome, other neutrophilic dermatoses (cryopyrin-associated periodic syndrome, Sweet syndrome, and pyoderma gangrenosum), urticarial vasculitis and chronic spontaneous urticaria as well as healthy control skin. Blood neutrophils from patients with Schnitzler's syndrome and controls were isolated, and NETosis was induced by phorbol 12-myristate 13-acetate (PMA). Also, NETosis of control neutrophils induced by symptomatic Schnitzler's syndrome sera, cytokines and sub-threshold PMA doses was studied. Immunofluorescence co-staining revealed widespread and substantial NET formation in lesional skin of Schnitzler's syndrome patients but absence of NETs in chronic spontaneous urticaria and control skin. Neutrophils undergoing NETosis were observed in the skin of other neutrophilic diseases too. Correspondingly, blood neutrophils from Schnitzler's syndrome patients showed significantly elevated NETosis rates compared to control neutrophils following stimulation with PMA. Increased NETosis correlated well with high levels of C-reactive protein (CRP). SchS patients with the lowest NETosis rates had persistent joint and bone pain despite IL-1 blockade. Stimulation of control neutrophils and sub-threshold PMA with sera of symptomatic Schnitzler's syndrome patients disclosed enhanced NETosis as compared to control sera. Our results suggest that the induction of NET formation by neutrophils contributes to skin and systemic inflammation and may support the resolution of local inflammation in Schnitzler's syndrome.

IntroductionSchnitzler's syndrome (SchS) is a disabling autoinflammatory disorder, characterized by a chronic urticarial rash, an M-protein, arthralgia, and other signs of systemic inflammation. Anti-interleukin-1 (IL-1) beta antibodies are highly effective, but the pathophysiology is still largely unknown. Here we studied the effect of in-vivo IL-1 inhibition on serum markers of inflammation and cellular immune responses.MethodsEight patients with SchS received monthly subcutaneous (s.c.) injections with 150 mg canakinumab for six months. Blood was drawn for measurement of serum markers of inflammation (12 times per patient) and for functional and phenotypic analysis of both freshly isolated and toll-like receptor (TLR)-ligand-stimulated peripheral blood mononuclear cells (PBMCs) (five times per patient). All data were compared to results of healthy controls.ResultsIL-6 levels in serum and in lysates of freshly isolated PBMCs and serum myeloid-related protein (MRP8)/14 and S100A12 levels correlated with disease activity. In vitro, LPS stimulation resulted in higher IL-6 and IL-1 beta production in PBMCs from symptomatic SchS patients compared to healthy controls, whereas patient cells were relatively hyporesponsive to poly:IC and Pam3Cys. The mRNA microarray of PBMCs showed distinct transcriptomes for controls, symptomatic patients and anti-IL-1-treated patients. Numbers of T- and B-cell subsets as well as M-protein concentrations were not affected by IL-1 inhibition. Free light chain levels were elevated in 4 out of 8 patients.ConclusionsIn conclusion, patient PBMCs are hyperresponsive to LPS, and clinical efficacy of IL-1 beta inhibition in patients with SchS is associated with in-vivo and ex-vivo suppression of inflammation. Interestingly, patient PBMCs showed divergent responses to TLR2/6, TLR3 and TLR4 ligands. Our data underscore that IL-1 beta plays a pivotal role in SchS.

IntroductionSchnitzler syndrome (SchS) is a rare, late-onset, acquired autoinflammatory disorder characterized by recurrent urticarial lesions, monoclonal gammopathy and systemic inflammation. Although interleukin-1 (IL-1) blockade with anakinra is considered as a standard of care, real-world data on long-term outcomes, biomarker utility and dose reduction remain limited. To evaluate the long-term efficacy and safety of anakinra, the utility of inflammatory biomarkers for disease monitoring, the feasibility of dose reduction and diagnostic delay in a cohort of Polish patients with SchS.MethodsWe conducted a retrospective observational study of 13 adults with SchS treated with anakinra at two Polish tertiary referral centers between 2018 and 2025. Clinical manifestations, laboratory parameters, treatment response, adverse events and longitudinal follow-up data were analyzed. Receiver operating characteristic (ROC) analyses were used to compare biomarkers of disease activity, including serum amyloid A (SAA), C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), fibrinogen, D-dimers and complete blood count (CBC)-derived inflammatory indices.ResultsAll 13 patients achieved rapid complete clinical remission within 48 hours of starting anakinra, accompanied by significant reductions in CRP and SAA. Remission was sustained over a median follow-up of 38.2 months (maximum 92.5 months), with no treatment discontinuations. In 3 patients (23%), dosing intervals were successfully extended to every 48-72 hours without loss of disease control. ROC analyses revealed that SAA showed the highest discriminatory power for distinguishing active disease from remission (AUC 0.974), outperforming ESR, fibrinogen and D-dimers. CBC-derived inflammatory indices declined markedly after treatment initiation but served mainly as adjunctive rather than primary monitoring tools. The therapy was well tolerated with no serious adverse events. The most frequent events were injection-site reactions, mild paradoxical psoriasis, transient neutropenia and consistent weight gain. Median diagnostic delay was 49 months.ConclusionsAnakinra provides highly effective and safe long-term disease control in SchS. SAA appears to be the most reliable biomarker for monitoring disease activity, while cautious interval prolongation may be feasible in selected patients in sustained remission. Furthermore, treatment-associated weight gain is a consistent clinical observation requiring attention.