Schnitzler's syndrome: diagnosis, treatment, and follow-up

Schnitzler's Syndrome-Diagnostic Experience, Approaches to Therapy, and Patient Management according to a Multicenter Russian Cohort

The objectives of the study were to present the experience of diagnosis, management, and therapy with IL-1 inhibitors in patients with Schnitzler's syndrome (SchS) according to a multicenter Russian cohort. An observational retrospective study for a 10-year period (2012-2022) involved 17 patients with SchS who were admitted to the hospital or were observed on an outpatient basis (eight women and nine men). The diagnosis of all of them corresponded to the Strasbourg diagnostic criteria. The age of patients ranged from 25 to 81 years (Me 53[46; 56]). The age at the time of the onset of the disease ranged from 20 to 72 years (Me 46[39; 54]), the duration of the disease before diagnosis ranged from 1 to 35 years (Me 6.5[3; 6]), in three patients it exceeded 10 years, in the rest it ranged from 1 to 8 years. Infectious and lymphoproliferative diseases, monogenic AIDs (CAPS, TRAPS, and HIDS) were excluded from all patients at the prehospital stage. The referral diagnosis for all of them was Still 's disease in adults. Clinical manifestations of the disease in all patients included fatigue, lethargy, fatigue, rash, and fever. In all patients, skin elements were urticular and were accompanied by itching in 6 (37.5%) patients. Bone pain was observed in 12 (70.6%) patients; arthralgias, in 16 (94.1%); arthritis, in 9 (52.9%); myalgia, in 7 (41.2%); and weight loss, in 4 (23.5%). Lymphadenopathy was detected in 6 (35.3%) patients; enlarged liver, in 6 (35.3%); pericarditis, in 4 (23.5%); angioedema, in 6 (35.3); redness and dryness in the eyes, in 3 (17.6%); sore throat, in 2 (11.8%); abdominal pain, in 1 (5.9%), distal polyneuropathy, in 2 (11.8%); paraesthesia, in 1 (5.9%); and chondritis of the auricles, in 1 (5.9%). Monoclonal gammopathy was detected in all patients with a secretion level of 2.9-15.1 g/L: IgMk (n = 10, 64.7%), less often IgMλ (n = 2), IgGk (n = 2), IgGλ (n = 1), and IgAλ (n = 1). Ben-Jones protein was not detected in any of them. All patients had an increased level of ESR and CRP. Before inclusion in the study, 16 patients received GCs (94.1%) with a temporary effect that disappeared with dose reduction or cancellation. Seven patients received cDMARDs, including methotrexate (5), hydroxychloroquine (2), and cyclophosphamide (1). All patients received NSAIDs and antihistamines, as well as biologics, including the anti-B-cell drug rituximab (1), monoclonal ABs to IgE omalizumab (2, 1 without effect and 1 with partial effect), IL-1i canakinumab (n = 10, 58.8%) subcutaneously once every 8 weeks, and anakinra (n = 4, 23.5%) subcutaneously daily. The duration of taking anakinra, which was prescribed in the test mode, ranged from 1 week to 2.5 months with a further switch to canakinumab in 3 patients. The duration of taking canakinumab at the time of analysis ranged from 7 months to 8 years. Against the background of treatment with IL-1i, 10 out of 11 (90.9%) patients received a complete response in terms of the clinical manifestations of the disease and a decrease in the level of ESR and CRP within a few days. In one patient, a partial response to the administration of anakinra was detected; however, after switching to canakinumab, the effect of treatment was finally lost. One patient received IL-6i for 8 months with an incomplete effect and a positive dynamics after switching to anakinra. Thus, anakinra was initially prescribed to four patients and changed to canakinumab in two of them; canakinumab was started as the first drug in seven patients. Treatment with anakinra was continued in two patients; with canakinumab, in nine patients. In one patient, due to the persistent absence of relapses, the interval between canakinumab injections was increased to 5 months without signs of reactivation; however, subsequently, against the background of stress and relapses of the disease, the intervals were reduced to 4 months. A healthy child was born by the same patient on the background of treatment. The tolerability of therapy was satisfactory in all patients, no SAEs were noted. SchS is a rare multifactorial/non-monogenic AID that should be differentiated from a number of rheumatic diseases and other AIDs. The onset in adulthood, the presence of recurrent urticarial rashes in combination with fever and other manifestations of a systemic inflammatory response are indications for examination for monoclonal secretion. The use of short- or long-acting IL-1i is a highly effective and safe option in the treatment of such patients.

[The most frequent febrile syndromes and autoinflammatory diseases in adulthood]

Autoinflammatory diseases are characterized by inflammatory manifestations in various organ systems, whereby recurrent febrile episodes, musculoskeletal complaints, gastrointestinal and cutaneous symptoms frequently occur accompanied by serological signs of inflammation. Autoinflammatory diseases include rare monogenic entities and multifactorial or polygenic diseases, which can manifest as a variety of symptoms in the course of time. Examples of monogenic autoinflammatory diseases are familial Mediterranean fever (FMF), cryopyrin-associated periodic syndrome (CAPS), tumor necrosis factor (TNF) receptor-associated periodic syndrome (TRAPS) and the recently described VEXAS (vacuoles, E1 enzyme, X‑linked, autoinflammatory and somatic) syndrome. For non-monogenically determined autoinflammatory diseases, the most important representatives in adulthood are adult-onset Still's disease (AOSD) and the Schnitzler syndrome, in which a polygenic susceptibility and epigenetic factors are more likely to play a role.

Schnitzler Syndrome: Insights into Its Pathogenesis, Clinical Manifestations, and Current Management

Schnitzler syndrome is a rare disorder characterized by a chronic urticarial rash associated with immunoglobulin M (IgM) monoclonal gammopathy. Schnitzler syndrome shares strong clinicopathologic similarities with monogenic IL-1-mediated autoinflammatory disorders and is now considered an acquired adult-onset autoinflammatory disease. The spectacular effect of interleukin-1 inhibitors demonstrates the key role of this cytokine in the pathogenesis of the disease. However, the physiopathology of Schnitzler syndrome remains elusive, and the main question regarding the relationship between autoinflammatory features and monoclonal gammopathy is still unanswered. The purpose of this narrative review is to describe what is currently known about the pathogenesis of this peculiar disease, as well as to address its diagnosis and management.

A case of Schnitzler syndrome with unusual immunoglobulin A gammopathy exacerbated by COVID-19 infection

Schnitzler syndrome (SchS) is a rare autoinflammatory disease characterized by chronic urticarial rash and monoclonal immunoglobulin M (IgM) or IgG gammopathy. Viruses, including COVID-19, activate the innate immune system, therefore SchS, in which the innate immune system is improperly activated, is hypothesized to be exacerbated by viral infection. However, there were no reported SchS cases exacerbated by any viral infection. Here, we report a SchS case with an unusual IgA gammopathy manifested and exacerbated by COVID-19 infection. This report advocates the need for recognizing unusual cases of SchS with monoclonal IgA, and following up on paraprotein like IgA even when it is initially undetectable in cases with SchS symptoms. We also hypothesize that existing autoinflammatory diseases may be exacerbated by COVID-19 infection in the case of a combination of these diseases.

Neutrophilic epitheliotropism, proposed as an auto-inflammatory condition of neutrophilic urticarial dermatosis including Schnitzler syndrome, is also observed in Japanese cases

Schnitzler syndrome (SchS) is a rare autoinflammatory disease characterized by bone pain, recurrent fever, leukocytosis, and elevated C-reactive protein, along with an urticaria-like rash and monoclonal immunoglobulin (Ig)M or IgG gammopathy. Notably, the condition is distinguished by a relatively persistent recurrent urticarial-like rash. Histopathological features observed in the skin comprise diffuse neutrophil infiltration into the dermis, absence of dermal edema, and vascular wall degeneration, all of which classify SchS as a neutrophilic urticarial dermatosis (NUD). Accumulated histological data from skin biopsies of patients with NUD have revealed a sensitive histopathological marker for NUD, acknowledged as neutrophilic epitheliotropism, which has been proposed as reflecting an autoinflammatory condition. In this report, we present three SchS patients: two men (ages 55 and 68) and a woman (age 75), all displaying neutrophilic epitheliotropism in their skin biopsy specimens. Additionally, a review of eight previously reported SchS cases in Japan identified neutrophilic epithliotropism in five cases. These findings suggest that the inclination of neutrophils toward the epithelial tissue could aid in confirming diagnoses of NUD in most cases that need to be differentiated from conventional urticaria. Consequently, we emphasize that acknowledging neutrophilic epithelial predilection as a hallmark of NUD is critical for expediting early diagnosis and appropriate treatment for SchS.

Neutrophil extracellular traps and neutrophilic dermatosis: an update review

Neutrophils have both antimicrobial ability and pathogenic effect in the immune system, neutrophil extracellular traps (NETs) formation is one of the representative behaviors of their dual role. NETs formation was triggered by pathogen-related components and pathogen non-related proteins as cytokines to exert its effector functions. Recent studies indicate that the pathogenicity of NETs contributed to several skin diseases such as psoriasis, Stevens-Johnson syndrome, toxic epidermal necrolysis, and neutrophilic dermatosis. Especially in neutrophilic dermatosis, a heterogeneous group of inflammatory skin disorders characterized with sterile neutrophilic infiltrate on dermis, NETs formation was reported as the way of participation of neutrophils in the pathogenesis of these diseases. In this review, we describe the different processes of NETs formation, then summarized the most recent updates about the pathogenesis of neutrophilic dermatosis and the participation of NETs, including pyoderma gangrenosum and PAPA syndrome, Behçet syndrome, hidradenitis suppurativa, Sweet Syndrome, pustular dermatosis and other neutrophilic dermatosis. Furthermore, we discuss the link between NETs formation and the development of neutrophilic dermatosis.

Schnitzler syndrome refractory to anakinra: successful treatment with canakinumab

Schnitzler syndrome (SchS) is a rare autoimmune and inflammatory disease mediated by interleukin-1 beta (IL-1β). Recurrent monoclonal gammopathy and chronic urticarial rash are the symptoms required for diagnosis according to the Strasbourg criteria. The low prevalence of this syndrome (around 300 cases have been reported) and confusion with other inflammatory disorders may delay the diagnosis for up to 5 years. Although the most effective treatment for SchS is anakinra, some patients do not respond to this treatment. We report a case of SchS in a 64-year-old woman with multiple episodes of fever, severe rash, erythema, arthralgia and dyspnea. The patient was successfully treated with canakinumab after anakinra intolerance and failure of colchicine, prednisone, methotrexate and dapsone. After the first dose of canakinumab the skin wounds rapidly improved and the patient did not require any concomitant treatments. The cause of SchS is still unknown and a differential diagnosis is recommended, especially with adult-onset Still´s disease due to their similar symptoms. Canakinumab, a specific anti-IL-1β antibody, blocks its binding to receptors, thereby preventing IL-1β-induced gene activation and production of inflammatory mediators. Canakinumab has proven to be an effective drug in SchS, providing an alternative to anakinra.

An unusual presentation of immunoglobulin A gammopathy in a patient with Schnitzler's syndrome

This case summarizes a 69-year-old woman who presented with a history of recurrent fevers, widespread urticarial rash and generalized myalgias for several years with an eventual diagnosis of Schnitzler's syndrome. This is a rare autoinflammatory condition which typically involves a chronic urticarial rash, monoclonal immunoglobulin M (IgM) or IgG gammopathy. Rapid improvement in above symptoms were noted with anakinra, an interleukin-1 receptor antagonist. We report an unusual case of a 69-year-old woman who presented with an isolated IgA monoclonal gammopathy.

[Autoinflammatory syndromes]

The concept of autoinflammation includes a heterogeneous group of monogenic and polygenic diseases. These are characterized by excessive activation of the innate immune system without antigen-specific T cells or autoantibodies. The diseases are characterized by periodic episodes of fever and increased inflammation parameters. Monogenic diseases include familial Mediterranean fever (FMF) and the newly described VEXAS (vacuoles, E1 enzyme, X‑linked, autoinflammatory, somatic) syndrome. Heterogeneous diseases include adult-onset Still's disease and Schnitzler syndrome. Treatment is aimed at preventing the excessive inflammatory reaction in order to avoid long-term damage, such as amyloid A (AA) amyloidosis.

Proposal of a new clinical entity: Paraprotein negative IL-1 mediated inflammatory dermatosis (PANID) that may precede Schnitzler syndrome

Schnitzler syndrome (SchS) is an autoinflammatory disease that is defined by the presence of 2 obligate criteria; an IgM or IgG monoclonal paraprotein and a chronic urticarial rash. Typically, there is an excellent clinical response to IL-1 antagonism. There are reports in the literature of a variant type of SchS that does not fulfil the 2 obligate criteria but responds to IL-1 blockade. Equally, there are reports of an urticarial rash preceding the development of a paraprotein by several years. We describe 3 cases in this manuscript. The first fits the Strasbourg diagnostic criteria of SchS, Simon and Asli (2013); however, with several decades of diagnostic delay. The second case at initial presentation did not fit the major criteria for SchS; however, later developed a monoclonal IgM. Finally we report, a third case that has not yet been confirmed to have a monoclonal IgM/IgG at the time of writing despite 12 years of symptoms and in whom a somatic autoinflammatory disorder remains within the differential. All cases responded strikingly to anakinra, an IL-1 receptor blocker. We propose a new clinical entity, paraprotein negative IL-1 mediated inflammatory dermatosis (PANID), that may act as a precursor or risk factor for the development of SchS or other autoinflammatory conditions.

Genetic Variants Leading to Urticaria and Angioedema and Associated Biomarkers

Advances in next generation sequencing technologies, as well as their expanded accessibility and clinical use over the past 2 decades, have led to an exponential increase in the number of identified single gene disorders. Among these are primary atopic disorders-inborn errors of immunity resulting in severe allergic phenotypes as a primary presenting feature. Two cardinal aspects of type I immediate hypersensitivity allergic reactions are hives and angioedema. Mast cells (MCs) are frequent primary drivers of these symptoms, but other cells have also been implicated. Even where MC degranulation is believed to be the cause, mediator-induced symptoms may greatly vary among individuals. Angioedema-particularly in the absence of hives-may also be caused by hereditary angioedema conditions resulting from aberrant regulation of contact system activation and excessive bradykinin generation or impairment of vascular integrity. In these patients, swelling can affect unpredictable locations and fail to respond to MC-directed therapies. Genetic variants have helped delineate key pathways in the etiology of urticaria and nonatopic angioedema and led to the development of targeted therapies. Herein, we describe the currently known inherited and acquired genetic causes for these conditions, highlight specific features in their clinical presentations, and discuss the benefits and limitations of biomarkers that can help distinguish them.

Therapy resistant urticaria as a long-term symptom of an incomplete Schnitzler syndrome

BACKGROUND

Recurring therapy resistant hives, accompanied by IgM-gammopathy, fever and joint pain can indicate Schnitzler syndrome, a rare autoimmune disorder. There is currently no approved treatment, but complete remission of symptoms can be induced with IL-1 antagonists.

CASE PRESENTATION

A patient with a history of chronic urticaria presented frequently at the outpatient clinic with severe hives and was treated unsuccessfully with antihistamines and omalizumab. After several years, additional symptoms such as joint pain, recurrent fever, and IgM-gammopathy developed. After the diagnostic criteria for Schnitzler syndrome were met, treatment with anakinra was initiated and resulted in an improvement of the symptoms. Shortly after the first injection, the patient developed large and painful erythematous lesions at the injection sites, leading to discontinuation of treatment and a rapid recurrence of symptoms. Subsequently, treatment with a longer-acting IL-1 antagonist (canakinumab) was initiated, resulting in a complete remission of symptoms.

CONCLUSION

This case report demonstrates that patients with urticarial symptoms that are not relieved by typical treatments should prompt repeated reassessments of the diagnosis, even years later, because gammopathy and other diagnostic criteria for Schnitzler syndrome can occur with a delay.

[Autoinflammatory syndromes]

The concept of autoinflammation includes a heterogeneous group of monogenic and polygenic diseases. These are characterized by excessive activation of the innate immune system without antigen-specific T cells or autoantibodies. The diseases are characterized by periodic episodes of fever and increased inflammation parameters. Monogenic diseases include familial Mediterranean fever (FMF) and the newly described VEXAS (vacuoles, E1 enzyme, X‑linked, autoinflammatory, somatic) syndrome. Heterogeneous diseases include adult-onset Still's disease and Schnitzler syndrome. Treatment is aimed at preventing the excessive inflammatory reaction in order to avoid long-term damage, such as amyloid A (AA) amyloidosis.

Urticaria: A Narrative Overview of Differential Diagnosis

Urticaria is an inflammatory skin disorder that may occur in isolation or associated with angioedema and/or anaphylaxis. Clinically, it is characterized by the presence of smooth, erythematous or blanching, itchy swelling, called wheals or hives, which greatly vary in size and shape and last less than 24 h before fading to leave normal skin. Urticaria is the consequence of mast-cell degranulation that can be caused by immunological or non-immunological mechanisms. From a clinical point of view, many skin conditions can mimic urticaria and their recognition is mandatory for a correct management and therapeutic approach. We have reviewed all of the main relevant studies which addressed differential diagnosis of urticarial, published until December 2022. The National Library of Medicine PubMed database was used for the electronic research. The present review offers a clinical narrative overview, based on the available literature, of the principal skin disorders that can be misdiagnosed as urticaria (mainly autoinflammatory or autoimmune disorders, drug-induced reactions, and hyperproliferative diseases). The aim of this review is to provide clinicians a useful tool for correctly suspecting and identifying all of these conditions.

Case report: Schnitzler-like syndrome without monoclonal gammopathy

Schnitzler syndrome is a rare autoinflammatory disorder characterized by urticarial rash, joint pain, recurrent fever, leucocytosis, elevated C-reactive protein (CRP) and serum amyloid A (SAA), and monoclonal IgM or IgG gammopathy. According to the Strasbourg criteria, both urticarial rash and gammopathy are mandatorily required for the diagnosis of Schnitzler’s syndrome. However, incomplete variants lacking either skin symptoms or monoclonal gammopathy have also been described. Here, we report a case in which the diagnosis of Schnitzler-like syndrome was made despite the absence of gammopathy, based on neutrophilic dermal inflammation, episodic and excessive increase in inflammatory parameters, and prompt response to anakinra, a soluble IL1 receptor antagonist (sIL-1RA). In addition, we detected neutrophil epitheliotropism, which is highly suggestive of autoinflammatory disease. Using whole-exome sequencing, we were unable to find a causative pathogenic mutation but did find several mutations possibly related to the inflammatory processes in this patient. This and other cases highlight that the existing Strasbourg criteria are too strict to capture Schnitzler-like syndromes that may respond well and rapidly to IL1 inhibition. Recurrent episodes of disease with normalization of inflammatory symptoms in the interval, rapid response to anakinra, and neutrophilic epitheliotropism in a lesional skin biopsy may help confirm the diagnosis of Schnitzler-like syndrome.

Similarities and differences in autoinflammatory diseases with urticarial rash, cryopyrin-associated periodic syndrome and Schnitzler syndrome

Cryopyrin-associated periodic syndromes (CAPS) and Schnitzler syndrome (SchS) are autoinflammatory diseases that present with urticaria-like rashes. CAPS is characterized by periodic or persistent systemic inflammation caused by the dysfunction of the NLRP3 gene. With the advent of IL-1-targeted therapies, the prognosis of CAPS has improved remarkably. SchS is considered an acquired form of autoinflammatory syndrome. Patients with SchS are adults of relatively older age. The pathogenesis of SchS remains unknown and is not associated with the NLRP3 gene. Previously, the p.L265P mutation in the MYD88 gene, which is frequently detected in Waldenström macroglobulinemia (WM) with IgM gammopathy, was identified in several cases of SchS. However, because persistent fever and fatigue are symptoms of WM that require therapeutic intervention, it is a challenge to determine whether these patients truly had SchS or whether advanced WM was misidentified as SchS. There are no established treatments for SchS. The treatment algorithm proposed with the diagnostic criteria is to use colchicine as first-line treatment, and systemic administration of steroids is not recommended due to concerns about side effects. In difficult-to-treat cases, treatment targeting IL-1 is recommended. If targeted IL-1 treatment does not improve symptoms, the diagnosis should be reconsidered. We hope that the efficacy of IL-1 therapy in clinical practice will serve as a stepping stone to elucidate the pathogenesis of SchS, focusing on its similarities and differences from CAPS.

Monoclonal Gammopathy of Undetermined Significance: A Comprehensive Review

Monoclonal Gammopathy of Undetermined Significance (MGUS) is an asymptomatic premalignant plasma cell dyscrasia with a predominate rise of the IgG immunoglobulin fraction without end-organ damage, often diagnosed incidentally. Despite its progression into various subsequent forms of hematological malignancies, MGUS remains underdiagnosed. A literature search was conducted using the Medline, Cochrane, Embase, and Google Scholar databases, including articles published until December 2022. Keywords used encompassed "Monoclonal Gammopathy of Undetermined Significance," "Plasma Cell dyscrasia," "Monoclonal gammopathy of renal significance," and "IgM Monoclonal gammopathy of Undetermined Significance," This study aimed to conduct a critical review to update knowledge regarding the pathophysiology, risk factors, clinical features, diagnostic protocols, complications, and current and novel treatments for MGUS. We recommend a multidisciplinary approach to manage MGUS due to the complexity of the illness's etiology, diagnosis, and therapy. This comprehensive review also highlights future prospects, such as developing screening protocols for at-risk populations, prevention of disease progression by early diagnosis through genome-wide association studies, and management using Daratumumab and NSAIDs.

The Expanding Spectrum of Autoinflammatory Diseases

Autoinflammatory diseases are systemic disorders caused by genetic or acquired abnormalities in certain signaling pathways of the innate immune system. Dysregulated activation of the inflammasome, i.e. molecular platforms responsible for the activation of caspase-1 and production of interleukin-1β, causes autoinflammation. Familial Mediterranean fever (FMF), the most common genetic autoinflammatory disease, is characterized by a periodic fever and serositis. The complex and heterogeneous genetic background of Japanese FMF patients, accompanied by potential overlap with other rheumatic diseases, suggests crosstalk between genetic and environmental factors. Recently, FMF has been recognized as being part of a spectrum of autoinflammatory syndromes named pyrin-associated autoinflammatory diseases. The discovery of a new monogenic autoinflammatory disease, A20 haploinsufficiency, may provide novel insights into early-onset Behçet's-like diseases. In contrast, adult-onset Still's disease and Schnitzler's syndrome are acquired autoinflammatory diseases without a monogenic abnormality. Although the concept of autoinflammatory diseases originally applied to monogenic hereditary recurrent fevers, it has been expanded to include non-genetic complex autoinflammatory diseases. Information concerning monogenic autoinflammatory diseases may prove useful for elucidating the molecular mechanisms underlying non-genetic autoinflammatory diseases.

Summary of the current status of clinically diagnosed cases of Schnitzler syndrome in Japan

BACKGROUND

Schnitzler syndrome is a rare disorder with chronic urticaria, and there is no report summarizing the current status in Japan.

METHODS

A nationwide survey of major dermatology departments in Japan was conducted in 2019. We further performed a systematic search of PubMed and Ichushi-Web, using the keywords "Schnitzler syndrome" and "Japan" then contacted the corresponding authors or physicians for further information.

RESULTS

Excluding duplicates, a total of 36 clinically diagnosed cases were identified from 1994 through the spring of 2022, with a male to female ratio of 1:1. The median age of onset was 56.5 years. It took 3.3 years from the first symptom, mostly urticaria, to reach the final diagnosis. The current status of 30 cases was ascertained; two patients developed B-cell lymphoma. SchS treatment was generally effective with high doses of corticosteroids, but symptoms sometimes recurred after tapering. Colchicine was administered in 17 cases and was effective in 8, but showed no effect in the others. Tocilizumab, used in six cases, improved laboratory abnormalities and symptoms, but lost its efficacy after several years. Rituximab, used in five cases, was effective in reducing serum IgM levels or lymphoma mass, but not in inflammatory symptoms. Four cases were treated with IL-1 targeting therapy, either anakinra or canakinumab, and achieved complete remission, except one case with diffuse large B-cell lymphoma.

CONCLUSIONS

Since Schnitzler syndrome is a rare disease, the continuous collection and long-term follow-up of clinical information is essential for its appropriate treatment and further understanding of its pathophysiology.

Monoclonal Gammopathies of Clinical Significance: A Critical Appraisal

Simple Summary

Monoclonal gammopathy of clinical significance (MGCS) refers to a recently coined term describing a complex and heterogeneous group of nonmalignant monoclonal gammopathies. These patients are characterized by the presence of a commonly small clone and the occurrence of symptoms that may be associated with the clone or with the monoclonal protein through diverse mechanisms. This is an evolving, challenging, and rapidly changing field. Patients are classified according to the key organ or system involved, with kidneys, skin, nerves, and eyes being the most frequently affected. However, multiorgan involvement may be the most relevant clinical feature at the presentation or during the course. This review delves into the definition, history, differential diagnosis, classification, prognosis, and treatment of this group of entities by analyzing the evidence accumulated to date from a critical perspective.

Abstract

Monoclonal gammopathies of clinical significance (MGCSs) represent a group of diseases featuring the association of a nonmalignant B cells or plasma cells clone, the production of an M-protein, and singularly, the existence of organ damage. They present a current framework that is difficult to approach from a practical clinical perspective. Several points should be addressed in order to move further toward a better understanding. Overall, these entities are only partially included in the international classifications of diseases. Its definition and classification remain ambiguous. Remarkably, its real incidence is unknown, provided that a diagnostic biopsy is mandatory in most cases. In fact, amyloidosis AL is the final diagnosis in a large percentage of patients with renal significance. On the other hand, many of these young entities are syndromes that are based on a dynamic set of diagnostic criteria, challenging a timely diagnosis. Moreover, a specific risk score for progression is lacking. Despite the key role of the clinical laboratory in the diagnosis and prognosis of these patients, information about laboratory biomarkers is limited. Besides, the evidence accumulated for many of these entities is scarce. Hence, national and international registries are stimulated. In particular, IgM MGCS deserves special attention. Until now, therapy is far from being standardized, and it should be planned on a risk and patient-adapted basis. Finally, a comprehensive and coordinated multidisciplinary approach is needed, and specific clinical trials are encouraged.

Improving Diagnosis and Clinical Management of Acquired Systemic Autoinflammatory Diseases

Systemic autoinflammatory diseases (SAID) are conditions caused by dysregulation or disturbance of the innate immune system, with neutrophils and macrophages the main effector cells. Although there are now more than 40 distinct, genetically defined SAIDs, the genetic/molecular diagnosis remains unknown for a significant proportion of patients with the disease onset in adulthood. This review focuses on new developments related to acquired/late onset SAID, including phenocopies of monogenic disorders, Schnitzler's syndrome, Adult onset Still's disease, VEXAS syndrome, and autoinflammatory complications associated with myelodysplastic syndrome.

Schnitzler Syndrome Presenting as a Fever of Unknown Origin with Elevated Alkaline Phosphatase Levels

Schnitzler syndrome (SchS) is a rare, acquired, autoinflammatory disease that is sometimes associated with a fever of unknown origin (FUO). Elevated alkaline phosphatase (ALP) stemming from abnormal bone remodeling is a characteristic laboratory finding of SchS and is included in the diagnostic criteria. However, its utility as a clue to the diagnosis of SchS has been under-emphasized. We herein report a case of SchS presenting with a FUO and highly elevated ALP concentration, which led to repeated, unnecessary liver biopsies.

New insights on multigenic autoinflammatory diseases

Autoinflammatory diseases are disorders of the innate immune system, which can be either monogenic due to a specific genetic mutation or complex multigenic due to the involvement of multiple genes. The aim of this review is to explore and summarize the recent advances in pathogenesis, diagnosis, and management of genetically complex autoinflammatory diseases, such as Schnitzler's syndrome; adult-onset Still's disease; synovitis, acne, pustulosis, hyperostosis, osteitis syndrome/chronic recurrent multifocal osteomyelitis/chronic non-bacterial osteomyelitis; Adamantiades-Behçet's disease; Yao syndrome; and periodic fever with aphthous stomatitis, pharyngitis, and adenitis syndrome. The PubMed database was screened for relevant articles using free text words and specific search strings. The search was limited to English-language articles, reporting the results of studies in humans, published through March 2021. Evidence from literature suggest that these rare multigenic autoinflammatory diseases can present with different clinical features and the diagnosis of these diseases can be challenging due to a combination of nonspecific manifestations that can be seen in a variety of other conditions. Diagnostic delays and disease complications may occur due to low disease awareness and the lack of pathognomonic markers. The pathogeneses of these diseases are complex and in some cases precise pathogenesis is not clearly understood. Conventional treatments are commonly used for the management of these conditions, but biologics have shown promising results. Biologics targeting proinflammatory cytokines including IL-1, IL-6, TNF-α, IL-17A and IL-18 have been shown to ameliorate signs and symptoms of different multigenic autoinflammatory diseases.

Malignant Evolution of Schnitzler Syndrome to Waldenström Macroglobulinemia: a Case Report

Introduction: Schnitzler syndrome (SchS), first described in 1972, is a rare autoinflammatory condition characterized by chronic urticaria and monoclonal gammopathy of IgM or, exceptionally, IgG profile. Additional features include recurrent fever, evidence of abnormal bone remodeling, a neutrophilic dermal infiltrate on skin biopsy, leukocytosis or elevated C-reactive protein, according to the Strasbourg criteria.

Case Presentation: We describe the case of a 56-year-old Caucasian male patient, who suffered from chronic urticaria, moderate-grade fever, severe generalized fatigue and arthralgias. After five years of chronic disease evolution, he was referred to the hematology department where he was found to have IgM kappa light chain monoclonal gammopathy. The constellation of symptoms, a negative rheumatologic workup, and the finding of IgM monoclonal gammopathy determined the diagnosis of Schnitzler syndrome. Bone marrow biopsy proved the association of Waldenström macroglobulinemia.

Conclusion: The main goal of our case report was to highlight the clinical features and treatment, with emphasis on the hematological aspects, to provide a better understanding and to raise awareness of Schnitzler syndrome among healthcare professionals.

Development and implementation of the AIDA international registry for patients with Schnitzler's syndrome

Objective

The present paper describes the design, development, and implementation of the AutoInflammatory Disease Alliance (AIDA) International Registry specifically dedicated to patients with Schnitzler's syndrome.

Methods

This is a clinical physician-driven, population- and electronic-based registry implemented for the retrospective and prospective collection of real-life data from patients with Schnitzler's syndrome; the registry is based on the Research Electronic Data Capture (REDCap) tool, which is designed to collect standardized information for clinical research, and has been realized to change over time according to future scientific acquisitions and potentially communicate with other existing or future similar registries.

Results

Since its launch, 113 centers from 23 countries in 4 continents have been involved. Fifty-seven have already obtained the approval from their local Ethics Committees. The platform counts 324 users (114 Principal Investigators, 205 Site Investigators, 2 Lead Investigators, and 3 data managers) at current (April 28th, 2022). The registry collects baseline and follow-up data using 3,924 fields organized into 25 instruments, including patient's demographics, history, clinical manifestations and symptoms, trigger/risk factors, laboratory, instrumental exams, therapies, socioeconomic information, and healthcare access.

Conclusions

This International Registry for patients with Schnitzler's syndrome facilitates standardized data collection, enabling international collaborative projects through data sharing and dissemination of knowledge; in turn, it will shed light into many blind spots characterizing this complex autoinflammatory disorder.

Unmet Medical Needs in Chronic, Non-communicable Inflammatory Skin Diseases

An estimated 20-25% of the population is affected by chronic, non-communicable inflammatory skin diseases. Chronic skin inflammation has many causes. Among the most frequent chronic inflammatory skin diseases are atopic dermatitis, psoriasis, urticaria, lichen planus, and hidradenitis suppurativa, driven by a complex interplay of genetics and environmental factors. Autoimmunity is another important cause of chronic skin inflammation. The autoimmune response may be mainly T cell driven, such as in alopecia areata or vitiligo, or B cell driven in chronic spontaneous urticaria, pemphigus and pemphigoid diseases. Rare causes of chronic skin inflammation are autoinflammatory diseases, or rheumatic diseases, such as cutaneous lupus erythematosus or dermatomyositis. Whilst we have seen a significant improvement in diagnosis and treatment, several challenges remain. Especially for rarer causes of chronic skin inflammation, early diagnosis is often missed because of low awareness and lack of diagnostics. Systemic immunosuppression is the treatment of choice for almost all of these diseases. Adverse events due to immunosuppression, insufficient therapeutic responses and relapses remain a challenge. For atopic dermatitis and psoriasis, a broad spectrum of innovative treatments has been developed. However, treatment responses cannot be predicted so far. Hence, development of (bio)markers allowing selection of specific medications for individual patients is needed. Given the encouraging developments during the past years, we envision that many of these challenges in the diagnosis and treatment of chronic inflammatory skin diseases will be thoroughly addressed in the future.

Development and Implementation of the AIDA International Registry for Patients With Undifferentiated Systemic AutoInflammatory Diseases

Objective

This paper points out the design, development and deployment of the AutoInflammatory Disease Alliance (AIDA) International Registry dedicated to pediatric and adult patients affected by Undifferentiated Systemic AutoInflammatory Diseases (USAIDs).

Methods

This is an electronic registry employed for real-world data collection about demographics, clinical, laboratory, instrumental and socioeconomic data of USAIDs patients. Data recruitment, based on the Research Electronic Data Capture (REDCap) tool, is designed to obtain standardized information for real-life research. The instrument is endowed with flexibility, and it could change over time according to the scientific acquisitions and potentially communicate with other similar tools; this platform ensures security, data quality and data governance.

Results

The focus of the AIDA project is connecting physicians and researchers from all over the world to shed a new light on heterogeneous rare diseases. Since its birth, 110 centers from 23 countries and 4 continents have joined the AIDA project. Fifty-four centers have already obtained the approval from their local Ethics Committees. Currently, the platform counts 290 users (111 Principal Investigators, 179 Site Investigators, 2 Lead Investigators, and 2 data managers). The Registry is collecting baseline and follow-up data using 3,769 fields organized into 23 instruments, which include demographics, history, symptoms, trigger/risk factors, therapies, and healthcare information access for USAIDs patients.

Conclusions

The development of the AIDA International Registry for USAIDs patients will facilitate the online collection of real standardized data, connecting a worldwide group of researchers: the Registry constitutes an international multicentre observational groundwork aimed at increasing the patient cohort of USAIDs in order to improve our knowledge of this peculiar cluster of autoinflammatory diseases. NCT05200715 available at https://clinicaltrials.gov/.

Monoclonal gammopathy of clinical significance: what the rheumatologist needs to know

Monoclonal proteins can provide important information on the diagnosis of several non-malignant systemic inflammatory disorders. At low concentration, they most commonly represent monoclonal gammopathy of undetermined significance (MGUS), whereas high concentrations often signify plasma cell myeloma or B-cell lymphoma. However, several rare inflammatory conditions associated with variable concentrations of monoclonal proteins, systemic symptoms, and organ dysfunction also exist. These conditions are termed monoclonal gammopathies of clinical significance (MGCS). Patients with MGCS might present to rheumatologists with undiagnosed systemic inflammatory disorders and the monoclonal protein provides an important, underappreciated clue for diagnosis. In this Review, we provide an approach to distinguishing MGCS from MGUS and lymphoid neoplasms, focusing on four rare MGCS that rheumatologists must recognise: scleromyxedema, Schnitzler's syndrome, idiopathic systemic capillary leak syndrome (also known as Clarkson's disease), and telangiectasias, elevated erythropoietin and erythrocytosis, monoclonal gammopathy, perinephric fluid collections, and intrapulmonary shunting (known as TEMPI) syndrome.

Cutaneous manifestations of monoclonal gammopathy

Monoclonal gammopathy associated with dermatological manifestations are a well-recognized complication. These skin disorders can be associated with infiltration and proliferation of a malignant plasma cells or by a deposition of the monoclonal immunoglobulin in a nonmalignant monoclonal gammopathy. These disorders include POEMS syndrome, light chain amyloidosis, Schnitzler syndrome, scleromyxedema and TEMPI syndrome. This article provides a review of clinical manifestations, diagnostics criteria, natural evolution, pathogenesis, and treatment of these cutaneous manifestations.

The Expanding Spectrum of Autoinflammatory Diseases

Autoinflammatory diseases are systemic disorders caused by genetic or acquired abnormalities in certain signaling pathways of the innate immune system. Dysregulated activation of the inflammasome, i.e. molecular platforms responsible for the activation of caspase-1 and production of interleukin-1β, causes autoinflammation. Familial Mediterranean fever (FMF), the most common genetic autoinflammatory disease, is characterized by a periodic fever and serositis. The complex and heterogeneous genetic background of Japanese FMF patients, accompanied by potential overlap with other rheumatic diseases, suggests crosstalk between genetic and environmental factors. Recently, FMF has been recognized as being part of a spectrum of autoinflammatory syndromes named pyrin-associated autoinflammatory diseases. The discovery of a new monogenic autoinflammatory disease, A20 haploinsufficiency, may provide novel insights into early-onset Behçet's-like diseases. In contrast, adult-onset Still's disease and Schnitzler's syndrome are acquired autoinflammatory diseases without a monogenic abnormality. Although the concept of autoinflammatory diseases originally applied to monogenic hereditary recurrent fevers, it has been expanded to include non-genetic complex autoinflammatory diseases. Information concerning monogenic autoinflammatory diseases may prove useful for elucidating the molecular mechanisms underlying non-genetic autoinflammatory diseases.

Schnitzler syndrome and Schnitzler-like syndromes

Schnitzler syndrome is a rare disease of adult-onset with main features including chronic urticarial rash, recurrent fever, arthralgia or arthritis, monoclonal gammopathy of undetermined significance (MGUS), and marked systemic inflammation. Schnitzler syndrome is often underdiagnosed. Patients with Schnitzler syndrome may present to dermatologists and allergists for urticaria, hematologists for MGUS, or rheumatologists for arthritis. It is important to recognize Schnitzler syndrome for its remarkable response to interleukin (IL)-1 blockade. Besides, many cases of Schnitzler-like syndromes do not meet the diagnostic criteria of classical Schnitzler syndrome but display excellent response to IL-1 inhibitors. The overly produced IL-1 is the result of a somatic mosaic gain of function mutation of NLRP3 (nucleotide-binding oligomerization domain [NOD]-like receptor [NLR] family pyrin domain containing 3) gene in some patients with Schnitzler-like syndromes. Inflammasome activation is evident in patients with classical Schnitzler syndrome although no NLRP3 gene mutation is identified. Collectively, Schnitzler syndrome and Schnitzler-like syndromes represent a spectrum of IL-1 mediated adult-onset autoinflammatory diseases.

Genetics of somatic auto-inflammatory disorders

Systemic autoinflammatory disorders (SAIDs) encompass a heterogeneous group of monogenic disorders characterized by recurrent episodes of systemic and organ-specific inflammation. Genetic studies have facilitated the identification of Mendelian forms of SAIDs but many patients still remain without a diagnosis. Recent studies have uncovered that somatic (acquired) mutations can cause later-onset SAIDs. In this review, we will discuss the current knowledge surrounding the genetics of these acquired auto-inflammatory disorders (AAIDs), with a focus on VEXAS, NLRP3-associated AAIDs and Schnitzler's syndrome and provide suggestions for future research in this field.

[Autoinflammation-differences between children and adults]

Autoinflammatory diseases present as multisystemic inflammation and often manifest in early childhood. In contrast, in a few diseases, e.g., the recently described VEXAS (vacuoles, E1 enzyme, X‑linked, autoinflammatory, somatic) syndrome, the first symptoms occur exclusively in adulthood. This article describes how the phenotypic expression and severity of individual autoinflammatory diseases differ depending on age. Furthermore, differences in the development of organ damage in children and adults are pointed out. In addition to the hereditary periodic fever syndromes, the clinical picture of deficiency of adenosine deaminase 2, the interferonopathies, periodic fever, aphthous stomatitis, pharyngitis, and adenitis syndrome as well as VEXAS and Schnitzler syndromes are highlighted.

AA amyloidosis complicating monoclonal gammopathies, an unusual feature validating the concept of "monoclonal gammopathy of inflammatory significance"?

INTRODUCTION

AL amyloidosis is caused by the proliferation of an immunoglobulin-secreting B cell clone. AA amyloidosis is a rare complication of chronic inflammation. However, some patients present with diseases combining monoclonal immunoglobulin production and chronic inflammation. The aim of this work was to describe cases of AA amyloidosis associated with monoclonal gammopathies.

PATIENTS AND METHODS

We reviewed all patients reported in French national amyloid centres presenting with AA amyloidosis and monoclonal gammopathy and performed a literature review. The quality of AA amyloidosis diagnosis and the causal relationship with monoclonal gammopathy were assessed.

RESULTS

In total, four patients from our centres and eight from the literature fulfilled the inclusion criteria. The haematological disorders presenting with monoclonal gammopathy were as follows: Waldenström macroglobulinaemia (n = 8), Schnitzler syndrome (n = 2), multiple myeloma (n = 1) and monoclonal gammopathy of undetermined significance (n = 1). Treatment strategies varied among the cases, with the treatment of the haematological disorder in 4 and anti-inflammatory treatment in 2.

CONCLUSION

Monoclonal gammopathies might be a rare and poorly known cause of AA amyloidosis. Such monoclonal gammopathies could be named "monoclonal gammopathies of inflammatory significance."

Treatment of Patients with Monoclonal Gammopathy of Clinical Significance

Simple Summary

Monoclonal gammopathy of clinical significance (MGCS) is a recently recognized clinical-pathological entity. Symptoms are caused by the presence of a monoclonal protein leading to high comorbidity. The affected organs vary according to the target antigen However, as most of the knowledge relies on case reports or short series; there is a lack of consensus regarding treatment approach. Here, we discuss MGCS other than renal (skin, ocular, neurologic, and bleeding disorders). We provide insights into the pathophysiology, diagnosis, treatment, and follow-up based on clinical cases. Finally, we discuss future directions in this field, such as potential novel therapeutic targets and prognosis of patients with MGCS.

Abstract

Monoclonal gammopathy of undetermined significance (MGUS) is defined as the presence of a monoclonal protein (M-protein) produced by a small amount of plasma cells. The majority of patients remain asymptomatic; however, a fraction of them develop clinical manifestations related to the monoclonal gammopathy despite not fulfilling criteria of multiple myeloma or other lymphoproliferative disorder. These patients constitute an emerging clinical issue coined as monoclonal gammopathy of clinical significance (MGCS). The mechanisms involved are poorly understood, and literature is scarce regarding management. The clinical spectrum involves symptoms related to renal, neurologic, skin, ocular, or bleeding manifestations, requiring a multidisciplinary approach. Treatment strategies rely on the basis of symptomatic disease and the M-protein isotype. In this review, we focus on MGCS other than renal, as the latter was earliest recognized and better known. We review the literature and discuss management from diagnosis to treatment based on illustrative cases from daily practice.

Refractory serum immunoglobulin M elevation during anti-interleukin (IL)-1- or IL-6-targeted treatment in four patients with Schnitzler syndrome

Schnitzler syndrome is characterized by chronic urticarial rash, neutrophilic dermal infiltrate, recurrent fever, bone pain, elevated C-reactive protein, and neutrophilic leukocytosis. The pathophysiology of Schnitzler syndrome is unknown, but it is considered to be an acquired form of an autoinflammatory disease because of the resemblance to clinical phenotypes of cryopyrin-associated periodic syndrome, in which a gain-of-function mutation in NLRP3 causes overexpression of interleukin (IL)-1β. Schnitzler syndrome is generally accompanied by a monoclonal immunoglobulin (Ig)M gammopathy with a long-term risk of lymphoproliferation that is possibly associated with an MYD88 mutation. Herein, we present the following four patients with Schnitzler syndrome: a 63-year-old woman; a 65-year-old man; a 43-year-old woman; and a 63-year-old woman. Each patient fulfilled the Strasbourg diagnostic criteria, but none of the patients had any mutation in NLRP3 or MYD88 detected in their peripheral blood. Although approved treatment options for Schnitzler syndrome are lacking, our patients were treated with IL-1-targeted therapy (anakinra or canakinumab) or anti-IL-6 (tocilizumab). The acute inflammatory clinical manifestations improved completely with canakinumab and partially with anakinra and tocilizumab, but the serum IgM levels were gradually increased in all patients, even during treatment. To determine whether treatment with anti-IL-1β or IL-6 prevents conversion to a hematopoietic disorder, further collection of cases and long-term follow-up will be needed.

Autoinflammation and autoimmunity across rheumatic and musculoskeletal diseases

Most rheumatic and musculoskeletal diseases (RMDs) can be placed along a spectrum of disorders, with autoinflammatory diseases (including monogenic systemic autoinflammatory diseases) and autoimmune diseases (such as systemic lupus erythematosus and antiphospholipid syndrome) representing the two ends of this spectrum. However, although most autoinflammatory diseases are characterized by the activation of innate immunity and inflammasomes and classical autoimmunity typically involves adaptive immune responses, there is some overlap in the features of autoimmunity and autoinflammation in RMDs. Indeed, some 'mixed-pattern' diseases such as spondyloarthritis and some forms of rheumatoid arthritis can also be delineated. A better understanding of the pathogenic pathways of autoinflammation and autoimmunity in RMDs, as well as the preferential cytokine patterns observed in these diseases, could help us to design targeted treatment strategies.

The combined prevalence of classified rare rheumatic diseases is almost double that of ankylosing spondylitis

BACKGROUND

Rare diseases (RDs) affect less than 5/10,000 people in Europe and fewer than 200,000 individuals in the United States. In rheumatology, RDs are heterogeneous and lack systemic classification. Clinical courses involve a variety of diverse symptoms, and patients may be misdiagnosed and not receive appropriate treatment. The objective of this study was to identify and classify some of the most important RDs in rheumatology. We also attempted to determine their combined prevalence to more precisely define this area of rheumatology and increase awareness of RDs in healthcare systems. We conducted a comprehensive literature search and analyzed each disease for the specified criteria, such as clinical symptoms, treatment regimens, prognoses, and point prevalences. If no epidemiological data were available, we estimated the prevalence as 1/1,000,000. The total point prevalence for all RDs in rheumatology was estimated as the sum of the individually determined prevalences.

RESULTS

A total of 76 syndromes and diseases were identified, including vasculitis/vasculopathy (n = 15), arthritis/arthropathy (n = 11), autoinflammatory syndromes (n = 11), myositis (n = 9), bone disorders (n = 11), connective tissue diseases (n = 8), overgrowth syndromes (n = 3), and others (n = 8). Out of the 76 diseases, 61 (80%) are classified as chronic, with a remitting-relapsing course in 27 cases (35%) upon adequate treatment. Another 34 (45%) diseases were predominantly progressive and difficult to control. Corticosteroids are a therapeutic option in 49 (64%) syndromes. Mortality is variable and could not be determined precisely. Epidemiological studies and prevalence data were available for 33 syndromes and diseases. For an additional eight diseases, only incidence data were accessible. The summed prevalence of all RDs was 28.8/10,000.

CONCLUSIONS

RDs in rheumatology are frequently chronic, progressive, and present variable symptoms. Treatment options are often restricted to corticosteroids, presumably because of the scarcity of randomized controlled trials. The estimated combined prevalence is significant and almost double that of ankylosing spondylitis (18/10,000). Thus, healthcare systems should assign RDs similar importance as any other common disease in rheumatology.