Case report: Schnitzler-like syndrome without monoclonal gammopathy

Neutrophilic Urticarial Dermatosis: A Window into Systemic Inflammation and Autoimmune Disorders

Neutrophilic urticarial dermatosis (NUD) is a distinctive dermatological manifestation that is commonly associated with systemic autoinflammatory and autoimmune diseases. This review comprehensively explores NUD in the context of five major conditions: Schnitzler syndrome, Still's disease, cryopyrin-associated periodic syndrome, systemic lupus erythematosus, and VEXAS syndrome. For each condition, a detailed discussion of the underlying mechanisms, clinical presentations, diagnostic criteria, and treatment strategies is provided. In addition, cases exhibiting features similar to NUD are emphasized, with a comprehensive examination of the pathological characteristics, particularly focusing on neutrophilic epitheliotropism. This review underscores the significance of identifying NUD as a potential indicator of systemic autoimmune disorders and discusses the role of skin biopsy and laboratory tests in diagnosing the underlying etiology. Finally, a diagnostic framework for NUD is proposed, highlighting the importance of a multidisciplinary assessment to ascertain the underlying systemic condition responsible for the dermatological manifestations. The objective of this review is to enhance the comprehension of NUD, thereby facilitating early diagnosis and the implementation of targeted strategies for affected patients.

Acquired autoinflammatory disorders: a dermatologist's perspective

Autoinflammatory disorders are characterized by a dysregulated and disproportionately heightened response by the innate immune system to PAMPs and DAMPs (pathogen- and damage-associated molecular patterns, respectively), with a crucial role played by neutrophils and macrophages in disease pathogenesis. Autoinflammatory disorders closely resemble connective tissue diseases (CTDs); however, tests for antinuclear antibodies, typically considered a marker of CTDs, are negative in autoinflammatory disorders. Many autoinflammatory disorders are monogenic and arise from inherited genetic mutations, resulting in autoinflammation. This is especially true for disorders presenting in childhood or early adulthood. However, with the relatively recent identification of VEXAS (vacuoles, E1 enzyme, X-linked, autoinflammatory, somatic) syndrome, the recognized genetic spectrum of these disorders has expanded, especially in the adult population, emphasizing that these mutations could either be inherited or acquired later in life. Additionally, many of the acquired autoinflammatory disorders, for example, adult-onset Still disease and Schnitzler syndrome, have a multifactorial pathogenesis and are typically polygenic. Many novel disorders are being described in this category, and the majority of them have prominent cutaneous manifestations - either at onset or during the course of disease - that are particularly important from a diagnostic point of view. In this review, we discuss the cutaneous findings of a few acquired autoinflammatory disorders, with a specific focus on adult-onset Still disease, VEXAS syndrome, Schnitzler syndrome, Kikuchi-Fujimoto disease and haemophagocytic lymphohistiocytosis.

Background and Clinical Features of a Unique and Mysterious Autoinflammatory Disease, Schnitzler Syndrome

Schnitzler syndrome is a unique autoinflammatory disease, of which 747 cases have been described worldwide to date. The main features of the syndrome are a triad of recurrent urticaria, monoclonal IgM gammopathy, systemic inflammation associated with recurrent fever, joint and bone pain, and atypical bone remodeling (osteosclerosis). The abnormal activation of the NLRP3 inflammasome produces IL-1, which drives the disease pathology, but it also involves IL-6 and IL-18. Unlike other autoinflammatory diseases, Schnitzler syndrome lacks evidence of the gene divergence causing the abnormal activation of NLRP3. However, mutations in the MEFV and MYD88 genes can be associated with the development of the disease. Due to its rarity, diagnosing the disease can be a challenging task. IL-1 inhibitors (i.e., anakinra, canakinumab, and rilonacept) are prominent in the treatment of the disease, but the IL-6 receptor inhibitor tocilizumab and the Bruton's tyrosine kinase inhibitor ibrutinib are also promising alternatives. In this summary article, we aim to provide a comprehensive overview of the clinical and molecular background of the disease and potential therapeutic targets, based on the cases reported so far. We diagnosed a patient who, to the best of our knowledge, represents the 748th documented case of this specific pathology. In the context of this patient, we would also like to draw attention to the potential pathogenic role of two novel gene mutations (variants of the MEFV gene "c.2084A>G" and the F2 gene "3'UTR c.*97G>A").

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.

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.