Serum biomarkers are similar in Churg-Strauss syndrome and hypereosinophilic syndrome

[Bronchial asthma and allergic rhinitis-The skin sample reveals a severe systemic disease]

This article reports the case of a 30-year-old female patient who suffered for many years from initially unspecific symptoms, such as recurrent, nonallergic and noninfectious sinusitis, late-onset bronchial asthma and pronounced lymphadenopathy; however, the correct diagnosis of eosinophilic granulomatosis with polyangiitis (EGPA) could only be made by histological investigations after the appearance of skin symptoms. The EGPA is a severe systemic disease which, if left untreated, can cause multiple organ damage and even be fatal. With adequate treatment the disease is mild in more than 90% of cases and patients can even completely recover. By making the correct diagnosis, the patient could be successfully treated and the risk of late manifestations and subsequent damage with a potentially fatal outcome was reduced.

The challenge of diagnosing and classifying eosinophilia and eosinophil disorders: A review

Eosinophilia is a feature of multiple conditions, both hematologic and non-hematologic, and may be associated with organ damage. The pathogenesis of eosinophilia can follow two distinct pathways. Primary eosinophilia is caused by a cell-intrinsic mechanism originating from clonal expansion of eosinophils through acquisition of a somatic mutation, such as FIP1L1-PDGFRA. In recent years, great progress has been made in the field of pathogenesis and molecularly targeted therapy of neoplastic eosinophilia. The diagnostic procedure should include, among other things, morphologic analysis of blood and bone marrow samples, cytogenetics and fluorescence in situ-hybridization tests to detect evidence of an acute or chronic myeloid or lymphoid disorder. Secondary eosinophilia follows a cell-extrinsic mechanism as a response to exogenous cytokines. In most clinical cases, peripheral blood eosinophilia is reactive and typically associated with non-hematological disorders such as infections, allergic conditions, connective tissue disorders, vasculitis, malignancy, or endocrinopathies. Nonetheless, the cause of most cases of hypereosinophilic syndrome remains unknown. In this article, we present a short review focused on differential diagnosis of eosinophilia and eosinophilic disorders. The diagnosis of eosinophilia is a challenge for physicians; thus this review may be useful in clinical practice.

HES and EGPA: Two Sides of the Same Coin

Elevated eosinophil counts are implicated in multiple diseases, from relatively prevalent organ-specific disorders such as severe eosinophilic asthma, to rare multisystem disorders such as hypereosinophilic syndrome (HES) and eosinophilic granulomatosis with polyangiitis (EGPA). Patients with these multisystem diseases, often associated with markedly elevated eosinophil counts, have a substantial risk of morbidity and mortality due to delayed diagnosis or inadequate treatment. A thorough workup of symptomatic patients presenting with elevated eosinophil counts is essential, although in some cases the differential diagnosis may remain difficult because of overlapping presentations between HES and EGPA. Notably, first- and second-line treatment options and response to therapy may differ for specific HES and EGPA variants. Oral corticosteroids are the first line of treatment for HES and EGPA, except when HES is the result of specific mutations driving clonal eosinophilia that are amenable to targeted treatment with a kinase inhibitor. Cytotoxic or immunomodulatory agents may be required for those with severe disease. Novel eosinophil-depleting therapies, such as those targeting interleukin 5 or its receptor, have shown great promise in reducing blood eosinophil counts, and reducing disease flares and relapses in patients with HES and EGPA. Such therapies could reduce the side effects associated with long-term oral corticosteroids or immunosuppressant use. This review provides a pragmatic guide to approaching the diagnosis and clinical management of patients with systemic hypereosinophilic disorders. We highlight practical considerations for clinicians and present cases from real-world clinical practice to show the complexity and challenges associated with diagnosing and treating patients with HES and EGPA.

Identification of new risk loci shared across systemic vasculitides points towards potential target genes for drug repurposing

OBJECTIVES

The number of susceptibility loci currently associated with vasculitis is lower than in other immune-mediated diseases due in part to small cohort sizes, a consequence of the low prevalence of vasculitides. This study aimed to identify new genetic risk loci for the main systemic vasculitides through a comprehensive analysis of their genetic overlap.

METHODS

Genome-wide data from 8467 patients with any of the main forms of vasculitis and 29 795 healthy controls were meta-analysed using ASSET. Pleiotropic variants were functionally annotated and linked to their target genes. Prioritised genes were queried in DrugBank to identify potentially repositionable drugs for the treatment of vasculitis.

RESULTS

Sixteen variants were independently associated with two or more vasculitides, 15 of them representing new shared risk loci. Two of these pleiotropic signals, located close to CTLA4 and CPLX1, emerged as novel genetic risk loci in vasculitis. Most of these polymorphisms appeared to affect vasculitis by regulating gene expression. In this regard, for some of these common signals, potential causal genes were prioritised based on functional annotation, including CTLA4, RNF145, IL12B, IL5, IRF1, IFNGR1, PTK2B, TRIM35, EGR2 and ETS2, each of which has key roles in inflammation. In addition, drug repositioning analysis showed that several drugs, including abatacept and ustekinumab, could be potentially repurposed in the management of the analysed vasculitides.

CONCLUSIONS

We identified new shared risk loci with functional impact in vasculitis and pinpointed potential causal genes, some of which could represent promising targets for the treatment of vasculitis.

Eosinophilic granulomatosis with polyangiitis - Advances in pathogenesis, diagnosis, and treatment

Eosinophilic granulomatosis with polyangiitis (EGPA) is a rare disease characterized by eosinophil-rich granulomatous inflammation and necrotizing vasculitis, pre-dominantly affecting small-to-medium-sized vessels. It is categorized as a primary antineutrophil cytoplasmic antibody (ANCA)-associated vasculitides (AAVs) but also shares features of hypereosinophilic syndrome (HES); therefore, both vessel inflammation and eosinophilic infiltration are suggested to cause organ damage. This dual nature of the disease causes variable clinical presentation. As a result, careful differentiation from mimicking conditions is needed, especially from HES, given the overlapping clinical, radiologic, and histologic features, and biomarker profile. EGPA also remains a diagnostic challenge, in part because of asthma, which may pre-dominate for years, and often requires chronic corticosteroids (CS), which can mask other disease features. The pathogenesis is still not fully understood, however, the interaction between eosinophils and lymphocytes B and T seems to play an important role. Furthermore, the role of ANCA is not clear, and only up to 40% of patients are ANCA-positive. Moreover, two ANCA-dependent clinically and genetically distinct subgroups have been identified. However, a gold standard test for establishing a diagnosis is not available. In practice, the disease is mainly diagnosed based on the clinical symptoms and results of non-invasive tests. The unmet needs include uniform diagnostic criteria and biomarkers to help distinguish EGPA from HESs. Despite its rarity, notable progress has been made in understanding the disease and in its management. A better understanding of the pathophysiology has provided new insights into the pathogenesis and therapeutic targets, which are reflected in novel biological agents. However, there remains an ongoing reliance on corticosteroid therapy. Therefore, there is a significant need for more effective and better-tolerated steroid-sparing treatment schemes.

Unmet needs and evidence gaps in hypereosinophilic syndrome and eosinophilic granulomatosis with polyangiitis

Hypereosinophilic syndrome (HES) and eosinophilic granulomatosis with polyangiitis (EGPA) are rare systemic inflammatory disorders with overlapping symptoms, elevated eosinophil counts, and heterogenous clinical presentations. Although progress has been made in recent years, there are substantial gaps in our understanding of the pathologic mechanisms involved in these diseases, as well as numerous unmet needs relating to both diagnosis and patient management. For example, in most cases of HES, the underlying cause of hypereosinophilia is unknown, while in EGPA, although a polygenic genetic susceptibility has been found, understanding of the pathogenic mechanisms remains largely elusive. Delineating differences between certain disease variants may be challenging, and there are no reliable predictive markers of disease course. In addition, the current diagnostic criteria for HES and classification criteria for EGPA are not easy to implement in a nonspecialist setting, and specialist referral pathways need to be signposted more clearly. Furthermore, disease-specific activity scores need to be developed to aid the assessment of treatment effects, and improved biomarkers are needed to aid with treatment stratification. In this review, we outline the limitations of our current understanding of HES and EGPA and highlight areas for future work, which ultimately should help improve patient management and outcomes.

Eosinophilic granulomatosis with polyangiitis: A review

Eosinophilic granulomatosis with polyangiitis (EGPA) is a rare, multi-system, inflammatory disease, belonging to the group of anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitides (AAV). Previously known as Churg-Strauss syndrome, EGPA is characterised by late-onset asthma, eosinophilia and vasculitis affecting small-to-medium vessels. This disease behaves differently in many aspects to the other AAV and is often excluded from AAV studies. The disease is poorly understood and, due to it rarity and unique manifestations, there has been limited research progress to optimise our understanding of its complex pathogenesis and ability to develop management options - although the success of interleukin-5 inhibitors such as Mepolizumab has been a welcome development. The pathophysiology also appears to be different to other forms of AAV and hence management strategies that work for AAV may not fully apply to this condition. There is no current standard therapy for EGPA although corticosteroids are almost universally used for treatment alongside other agents and encouraging modes of treatment continue to evolve beyond glucocorticoid immunosuppression (including interleukin-5 inhibition). There is therefore a significant ongoing unmet need for efficacious steroid-sparing immunosuppressing agents. The prognosis also diverges from other forms of AAV, and we discuss the pathophysiology, clinical features and diagnosis, management and prognosis in this article.

Distinct features of hypereosinophilic syndrome with neuropathy from eosinophilic granulomatosis with polyangiitis

BACKGROUND AND OBJECTIVES

Hypereosinophilic syndrome (HES) and eosinophilic granulomatosis with polyangiitis (EGPA) have overlapping clinical considerations, which frequently involve peripheral neuropathy. The current study aimed to discriminate between the clinicopathological features of HES and EGPA, focusing on the mechanism of peripheral nerve damage.

METHODS

A total of 53 patients who underwent nerve biopsies at our laboratory were examined: nine patients with idiopathic HES (iHES), three patients with reactive HES, 14 patients with myeloperoxidase-anti-neutrophil cytoplasmic antibody (ANCA)-positive EGPA, and 27 patients with negative EGPA. Nerve biopsies were performed using light and electron microscopy.

RESULTS

Polyneuropathy was more common than mononeuritis multiplex in iHES, which differed from that in ANCA-negative EGPA groups (p = 0.012). Nerve biopsies showed that iHES was associated with neuropathy features such as rare vasculitis and non-vasculitic eosinophilic infiltrates, which differed from those of ANCA-negative EGPA. Fibrinoid necrosis was found only in the reactive HES and ANCA-positive groups. The percentage of endoneurial vessels occluded with eosinophils tended to be higher in iHES (1.8%) than in ANCA-positive EGPA (0%) and negative EGPA (0.7%). In a patient with ANCA-negative EGPA, the endoneurial vessels were occluded with platelets, fibrinoid materials, and eosinophils, demonstrating the morphology of eosinophil extracellular traps.

CONCLUSION

iHES with neuropathy showed a pattern more similar to polyneuropathy than mononeuritis multiplex, which is dominant in ANCA-negative EGPA, and tended to show vasculitis in the peripheral nerves less frequently compared with EGPA. Eosinophilic infiltration and endoneurial vascular occlusion by eosinophils may cause nerve damage.

A diagnostic score for eosinophilic granulomatosis with polyangiitis among eosinophilic disorders

BACKGROUND

Eosinophilic granulomatosis with polyangiitis (EGPA) is a form of systemic vasculitis with eosinophilic inflammation. However, existing classification criteria are all designed to classify EGPA among vasculitis and there is no established method distinguishing EGPA from other eosinophilic disorders. The aim of the present study was to propose a scoring system to differentiate EGPA among eosinophilic disorders.

METHODS

Non-supervised hierarchical clustering using Ward's method and principal component analysis (PCA) were performed for 19 clinical parameters of 58 patients with eosinophilia-related diseases at a tertiary university hospital. The newly proposed scoring system was externally validated in 40 patients at another tertiary institution.

RESULTS

Two distinct clusters were identified, and clinical features including peripheral neuropathy, asthma, skin involvement, lung involvement, rheumatoid factor (RF) positivity, myeloperoxidase (MPO)-anti-neutrophil cytoplasmic antibody (ANCA) positivity, IgE elevation, C-reactive protein (CRP) elevation, and vasculitis pathological findings were predominantly observed in one of these clusters (p < 0.05). Ten features defining the cluster with a high rate of vasculitis were weighted by PCA to create the E-CASE (EGPA classification among systemic eosinophilia) scoring system, on a 16-point scale. Based on the distribution of scores in the primary cohort, we defined an E-CASE score ≥12 as positive, ≤ 8 as negative, and 9-11 as undeterminable. The sensitivity and specificity of the E-CASE score in the validation cohort were 93.3% and 100%, respectively.

CONCLUSIONS

We developed and verified a novel scoring system for differentiating EGPA from other types of eosinophilic disorders.

Acute exacerbation of idiopathic hypereosinophilic syndrome following asymptomatic coronavirus disease 2019: a case report

BACKGROUND

Previous research has suggested that some autoimmune diseases develop after the occurrence of coronavirus disease 2019. Hypereosinophilic syndrome is a rare disease presenting with idiopathic eosinophilia and multiple organ involvement, including the skin, lungs, gastrointestinal tract, heart, and nervous system. The diagnosis of idiopathic hypereosinophilic syndrome poses a dilemma because clinical manifestation and serum biomarkers are similar to those of eosinophilic granulomatosis with polyangiitis. Only a few cases have been reported where coronavirus disease 2019 may have caused the new onset or exacerbation of eosinophilic granulomatosis with polyangiitis or idiopathic hypereosinophilic syndrome.

CASE PRESENTATION

We present the case of a 48-year-old Japanese woman with history of asthma who developed deteriorating symptoms of insidiously developed idiopathic hypereosinophilic syndrome following asymptomatic coronavirus disease 2019. She developed acute-onset back pain, tachycardia, abdominal discomfort, loss of appetite, weight loss, skin rash on the back, and numbness of the extremities 3 days after the quarantine period. Extreme hypereosinophilia with multiple abnormal findings including pulmonary ground-glass opacity lesions and mononeuritis multiplex was consistent with hypereosinophilic syndrome. Normal cellularity with eosinophilic proliferation in the bone marrow and negative FIP1L1-PDGFRA raised the diagnosis of idiopathic hypereosinophilic syndrome. Although the patient tested negative for anti-neutrophilic cytoplasmic antibodies and skin biopsy was negative for vasculitis, eosinophilic granulomatosis with polyangiitis could not be excluded. Since glucocorticoids are a standard therapy for both idiopathic hypereosinophilic syndrome and eosinophilic granulomatosis with polyangiitis, we initiated glucocorticoids following a multidisciplinary discussion.

CONCLUSION

Although the relationship between asymptomatic coronavirus disease 2019 and acute idiopathic hypereosinophilic syndrome exacerbation was uncertain, the chronological order of the symptomatic development suggested a possible link. More clinical cases and population-based studies are needed to determine the potential effect of coronavirus disease 2019 on autoimmune diseases.

The Diagnostic Challenge of Eosinophilic Granulomatosis With Polyangiitis Presenting as Acute Eosinophilic Myocarditis: Case Report and Literature Review

Eosinophilic granulomatosis with polyangiitis (EGPA) is a systemic vasculitis involving small-to-medium-sized vessels characterized by asthma, vasculitis, and peripheral eosinophilia. EGPA-associated eosinophilic myocarditis (EM) occurs rarely, yet can be fatal if left untreated. Moreover, the accurate diagnosis of EGPA-associated EM without vasculitis is exceptionally difficult because of the overlapping features with EM of other causes. We report a case of probable EGPA with subclinical neurological involvement that presented with acute EM. The constellation of peripheral eosinophilia, left ventricular dysfunction, and normal epicardial coronary arteries raised suspicion of acute EM, which was confirmed by cardiac magnetic resonance (CMR) investigation and endomyocardial biopsy (EMB). Prompt systemic administration of corticosteroids completely restored and normalized myocardial structure and function. Although the patient's history suggested the presumed hypersensitivity myocarditis, EMB revealed EM without vasculitis, not hypersensitivity, leading to a tentative diagnosis of idiopathic hypereosinophilic syndrome. Interestingly, the characteristic findings of vasculitis on CMR imaging strongly suggested EGPA-associated EM. Although the patient had no clinical neurological manifestations, a nerve conduction study confirmed mononeuritis multiplex, leading to the final diagnosis of probable EGPA. Therefore, this case highlights the diagnostic challenge associated with EGPA and the diagnostic synergy of CMR and EMB for an exploratory diagnosis of EGPA-associated EM.

Renal Involvement as Rare Acute Tubulointerstitial Nephritis in a Patient with Eosinophilic Disorder Treated with Early Add-on Administration of Mepolizumab

A 39-year-old man presented with peripheral eosinophilia, pulmonary eosinophilic infiltrate, and renal failure due to acute tubulointerstitial nephritis (TIN). He had experienced childhood asthma and was negative for anti-neutrophil cytoplasmic antibody (ANCA). He was tentatively diagnosed with ANCA-negative eosinophilic granulomatous polyangiitis (EGPA) or idiopathic hypereosinophilic syndrome (HES). Renal involvement of isolated TIN with eosinophil infiltration is rare in EGPA and HES and does not seem to have a good prognosis in the literature. However, his condition improved well with corticosteroids and mepolizumab. The revised classification of EGPA based on the etiology should dictate the proper treatment in suspected EGPA patients with nonsystemic vasculitis.

The causes of a peripheral blood eosinophilia in a secondary care setting

BACKGROUND

A peripheral blood eosinophilia of greater than 1.0 × 10⁹ /L is relatively unusual and offers a clue to the underlying diagnosis. In 2003, we established a specialist service to diagnose unexplained eosinophilia.

OBJECTIVE

To describe the causes of an eosinophilia in our service and the diagnostic algorithm we developed.

METHODS

Subjects were referred by physician colleagues across a range of specialties and undertook standard investigations following a semi-structured protocol. Data were extracted from a bespoke database.

RESULTS

Three hundred and eighty two subjects were referred over a 17-year period. Average age was 54 years and 183 (48%) of subjects were female, with 21 of 25 (84%) females in the idiopathic eosinophilic pneumonia group (p < 0001), 22 of 30 (73%) females in the gastrointestinal disease group (p < .008), but 11 of 37 (30%) females in the eosinophilic granulomatosis with polyangiitis group (p < .04). A diagnosis was assigned after systematic evaluation using a pre-defined algorithm in 361 (94.5%) of cases. Fungal allergy (82 subjects: 21%), parasitic infection (61 subjects: 16%) and severe eosinophilic asthma (50 subjects: 13%) were the three commonest individual diagnoses. Hypereosinophilic syndrome (HES) disease including eosinophilic granulomatosis with polyangiitis (EGPA) accounted for 85 subjects (20%) of which seven subjects (2%) had myeloproliferative disease (M-HES). A high IgE was common, and 79 (91%) of subjects with complete data who had an IgE of ≥1000 IU/L had fungal allergy or parasite infection. The serum tryptase was raised in 44 of 302 (14.5%) of individuals across all diagnostic groups, though none had mastocytosis.

CONCLUSION

A diagnosis of an unexplained eosinophilia can usually be determined using as semi-structured algorithm. Parasitic infection and fungal allergy often with severe eosinophilic asthma were common causes, whereas HES, particularly myeloproliferative, disease was relatively rare.

What does elevated TARC/CCL17 expression tell us about eosinophilic disorders?

Eosinophilic disorders encompass a large spectrum of heterogeneous diseases sharing the presence of elevated numbers of eosinophils in blood and/or tissues. Among these disorders, the role of eosinophils can vary widely, ranging from a modest participation in the disease process to the predominant perpetrator of tissue damage. In many cases, eosinophilic expansion is polyclonal, driven by enhanced production of interleukin-5, mainly by type 2 helper cells (Th2 cells) with a possible contribution of type 2 innate lymphoid cells (ILC2s). Among the key steps implicated in the establishment of type 2 immune responses, leukocyte recruitment toward inflamed tissues is particularly relevant. Herein, the contribution of the chemo-attractant molecule thymus and activation-regulated chemokine (TARC/CCL17) to type 2 immunity will be reviewed. The clinical relevance of this chemokine and its target, C-C chemokine receptor 4 (CCR4), will be illustrated in the setting of various eosinophilic disorders. Special emphasis will be put on the potential diagnostic, prognostic, and therapeutic implications related to activation of the TARC/CCL17-CCR4 axis.

Eosinophil Knockout Humans: Uncovering the Role of Eosinophils Through Eosinophil-Directed Biological Therapies

The enigmatic eosinophil has emerged as an exciting component of the immune system, involved in a plethora of homeostatic and inflammatory responses. Substantial progress has been achieved through experimental systems manipulating eosinophils in vivo, initially in mice and more recently in humans. Researchers using eosinophil knockout mice have identified a contributory role for eosinophils in basal and inflammatory processes and protective immunity. Primarily fueled by the purported proinflammatory role of eosinophils in eosinophil-associated diseases, a series of anti-eosinophil therapeutics have emerged as a new class of drugs. These agents, which dramatically deplete eosinophils, provide a valuable opportunity to characterize the consequences of eosinophil knockout humans. Herein, we comparatively describe mouse and human eosinophil knockouts. We put forth the view that human eosinophils negatively contribute to a variety of diseases and, unlike mouse eosinophils, do not yet have an identified role in physiological health; thus, clarifying all roles of eosinophils remains an ongoing pursuit.

Eosinophilic granulomatosis with polyangiitis: understanding the disease and its management

Eosinophilic granulomatosis with polyangiitis is characterized by asthma, blood and tissue eosinophilia and small-vessel vasculitis. The clinical presentation is variable, but two main clinic-pathologic subsets can be distinguished: one hallmarked by positive ANCA and predominant 'vasculitic' manifestations (e.g. glomerulonephritis, purpura and mononeuritis multiplex) and the other by negative ANCA and prominent 'eosinophilic' manifestations (e.g. lung infiltrates and cardiomyopathy). The pathogenesis is not fully understood but probably results from the interplay between T and B cells and eosinophils. Eosinophilic granulomatosis with polyangiitis must be differentiated from several conditions, including hypereosinophilic syndromes and other small-vessel vasculitides. The overall survival is good; however, patients frequently relapse and have persistent symptoms. The recently developed monoclonal antibodies targeting B cells and eosinophilopoietic cytokines such as IL-5 are emerging as valid alternatives to conventional immunosuppressive therapies. In this review, we discuss the essential features of eosinophilic granulomatosis with polyangiitis, with particular respect to the most relevant issues concerning clinical presentation and management.

Role of Cytokines in EGPA and the Possibility of Treatment with an Anti-IL-5 Antibody

Eosinophilic granulomatosis with polyangiitis (EGPA) is a type of systemic vasculitis with eosinophilia in the peripheral blood, which is preceded by bronchial asthma or allergic disease. EGPA is pathologically characterized by microangiopathy granulomatosis vasculitis. Vasculitis can be exacerbated and cause central nervous system and cardiovascular disorders and gastrointestinal perforation. Histological examination reveals eosinophil infiltration and granulomas in lesions in areas such as the lung, nervous system, and skin. Laboratory tests show inflammatory findings such as C-reactive protein (CRP) elevation, increased eosinophils, elevated serum IgE, and elevated myeloperoxidase-anti-neutrophil cytoplasmic antibodies (MPO-ANCA). MPO-ANCA is positive in approximately 40-70% of cases of this disease. EGPA is a necrotizing vasculitis that affects small- and medium-sized blood vessels; however, it differs from other types of ANCA-related vasculitis (such as microscopic polyangiitis and granulomatosis) because it is preceded by bronchial asthma and eosinophilia in the blood and tissues. Treatment with immunosuppressive agents such as steroids or cyclophosphamide depends on the Five Factor Score, which predicts the prognosis and severity of the condition. If the effect of appropriate treatment with steroids is insufficient, the anti-interleukin-5 antibody mepolizumab can be administered. The combination of mepolizumab with standard treatment leads to a significantly longer duration of remission, a higher proportion of patients who achieve sustained remission, and less steroid use than with a placebo.

Updates in antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis for the ENT surgeon

ENT involvement is common in ANCA-associated vasculitis (AAV), particularly in GPA and EGPA. Early recognition and treatment is important for good outcomes, yet evidence suggests that UK ENT surgeons may not consistently recognise the early features of AAV, despite a similar incidence to vestibular schwannoma. AAV is a rapidly advancing field, with significant developments in the understanding of its pathogenesis, classification and treatment over the past decade. Relevant vasculitis mimics are also discussed with a particular focus on the increasing prevalence of vasculitis mimics driven by an increase in recreational cocaine use, as well as the emergence and reclassification of several other vasculitis mimics in the head and neck. This article reviews key recent updates in the vasculitis literature, with a particular focus on those relevant to recognition and diagnosis of AAV for the ENT surgeon. Strengths and limitations of relevant diagnostic testing are discussed, and a method of evaluation of patients with features of AAV presenting to ENT services is outlined.

Mechanisms of glucocorticoid resistance in hypereosinophilic syndromes

BACKGROUND

Glucocorticoids (GC) are considered first-line therapy for most patients with hypereosinophilic syndrome (HES). Although response rates are generally high, many patients require moderate to high doses for control of eosinophilia and symptoms, and up to 15% of patients do not respond at all. Despite this, little is known about the mechanisms of GC resistance in patients with HES.

OBJECTIVE

To explore the aetiology of GC resistance in HES.

METHODS

Clinical data and samples from 26 patients with HES enrolled on a prospective study of GC responsiveness and 23 patients with HES enrolled on a natural history study of eosinophilia for whom response to GC was known were analysed retrospectively. Expression of GC receptor isoforms was assessed by quantitative RT-PCR in purified eosinophils. Serum cytokine levels were quantified by suspension array assay in multiplex.

RESULTS

Despite an impaired eosinophil response to GC after 7 days of treatment, the expected rise in absolute neutrophil count was seen in 7/7 GC-resistant patients, suggesting that GC resistance in HES is not a global phenomenon. Eosinophil mRNA expression of glucocorticoid receptor (GR) isoforms (α, β, and P) was similar between GC-sensitive (n = 20) and GC-resistant (n = 9) patients with HES. Whereas geometric mean serum levels were also comparable between GC-r (n = 11) and GC-s (n = 19) for all cytokines tested, serum IL-5 levels were >100 pg/mL only in GC-r patients.

CONCLUSIONS AND CLINICAL RELEVANCE

These data suggest that the mechanism of GC resistance in HES is not due to a global phenomenon affecting all lineages, but may be due, at least in some patients, to impairment of eosinophil apoptosis by increased levels of IL-5.

Eosinophilic disorders: evaluation of current classification and diagnostic criteria, proposal of a practical diagnostic algorithm

Eosinophilic disorders represent a group of pathologic conditions with highly heterogeneous pathophysiology and clinical presentation and variable prognosis, ranging from asymptomatic or mild, to severe and complex cases, with fatal outcome. Interest in this group of disorders has increased during the last two decades, with consistent progress made regarding understanding of molecular mechanisms, refining of diagnostic criteria, classification and evaluation of therapeutic options. There are still many gaps and difficulties in evaluating eosinophilic syndromes and diseases in medical practice. The disease prognosis depends mainly on the cause and mechanism of eosinophilia, on severity of organ dysfunction and on accurate diagnosis and response to treatment. Besides primary hypereosinophilic syndromes and secondary (reactive) eosinophilias, many associated or idiopathic forms have been described, making this topic a complex and difficult medical entity. An important aim of the experts in the field is to agree upon a more clear and practically useful classification, a better characterization of various phenotypes and endotypes of eosinophilic diseases and to identify novel biomarkers and more effective therapies. The aim of this paper is to review recent data from the literature regarding definition, classification and diagnosis criteria of eosinophilic diseases and to propose a revised and updated diagnostic algorithm useful in clinical practice.

Mepolizumab for the treatment of eosinophilic granulomatosis with polyangiitis

INTRODUCTION

Eosinophilic granulomatosis with polyangiitis (EGPA) is a rare antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis characterized by asthma, hypereosinophilia, and progressive multiorgan involvement. Although not fully elucidated, advancement in our understanding of the pathophysiology of EGPA has led to the development of multiple new treatment targets.

AREAS COVERED

Herein we review the epidemiology, clinical manifestations, pathophysiology, treatments, and ongoing research in the management of EGPA. The central role of Interleukin-5 (IL-5) in the development and maintenance of hypereosinophilia will be discussed. The value of mepolizumab, an anti-IL-5 monoclonal antibody, in the treatment of EGPA is reviewed in detail.

EXPERT OPINION

The available literature supports the use of mepolizumab for the induction and maintenance of remission of refractory, relapsing, or glucocorticoid-dependent EGPA with potentially greater benefit in those who are ANCA-positive or those with greater eosinophilia ( ≥ 150 cells/ μ L). Despite these positive results, relapses remain frequent, and the need for both short- and long-term glucocorticoid use remains common. More research is needed to address these needs and determine the precise role of mepolizumab.

Treatment of Eosinophilic Granulomatosis with Polyangiitis: A Review

Eosinophilic granulomatosis with polyangiitis (formerly Churg-Strauss syndrome) is a rare type of anti-neutrophil cytoplasm antibody-associated vasculitis. Nevertheless, eosinophilic granulomatosis with polyangiitis stands apart because it has features of vasculitis and eosinophilic disorders that require targeted therapies somewhat different from those used for other anti-neutrophil cytoplasm antibody-associated vasculitides. Considerable advances have been made in understanding the underlying pathophysiology of eosinophilic granulomatosis with polyangiitis that have highlighted the key role of eosinophils and opened new therapeutic opportunities. Its conventional treatment relies mainly on agents that decrease inflammation: corticosteroids and immunosuppressant adjunction for severe manifestations. New therapeutic approaches are needed for refractory disease, relapses and issues associated with corticosteroid dependence, especially for asthma manifestations. Drugs under evaluation mostly target eosinophils and B cells. Results of low-evidence-based trials suggested possible efficacies of biologicals: B-cell-blocking rituximab and anti-immunoglobulin E omalizumab. Recently, the first large-scale randomised controlled trial on eosinophilic granulomatosis with polyangiitis proved the efficacy of anti-interleukin-5 mepolizumab. That finding opens a new era in eosinophilic granulomatosis with polyangiitis management, with mepolizumab approval but also in future drug evaluations and trial designs for eosinophilic granulomatosis with polyangiitis. Additional studies are needed to determine which patients would benefit most from targeted therapies and achieve personalised treatment for patients with eosinophilic granulomatosis with polyangiitis. Herein, we review eosinophilic granulomatosis with polyangiitis characteristics and provide an overview of established and novel pharmacological agents.

Serum cytokine and chemokine levels in patients with eosinophilic granulomatosis with polyangiitis, hypereosinophilic syndrome, or eosinophilic asthma

OBJECTIVES

The pathogenesis of eosinophilic granulomatosis with polyangiitis (EGPA) remains poorly understood, and may overlap with eosinophilic asthma and primary hypereosinophilic syndrome (HES). The aim of this study was to analyse a panel of serum cytokines and chemokines as markers of disease activity in patients with these conditions.

METHODS

The levels of 54 cytokines and chemokines were measured in the sera of 40 patients with active EGPA, 10 of these patients during inactive disease, 6 patients with HES, 8 with asthma, and 10 healthy controls. Serum cytokine/chemokines measured included interleukin (IL)-1α, 1β, 3, 4, 5, 6, 8, 13, 15, 17A, 17E(25), 18, 23 and 33, soluble IL-2 receptor alpha, eotaxin-1 (CCL11), -2 (CCL24) and -3 (CCL26), macrophage-derived chemokine (MDC/CCL22), macrophage inflammatory protein (MIP)-1a and -1b, and tumour necrosis factor (TNF)-α. Results were compared between disease and control groups using regression analysis, with Bonferroni correction for multiple comparisons (significant p value ≤0.00093).

RESULTS

Significant differences were observed only in serum levels of MDC, IL-8, MIP-1a and -1b, TNF-α, each of which were lower in patients with active EGPA than in healthy controls (p<0.0001). Differences between patients with active disease and other disease groups did not reach significance. Paired comparisons between sera from patients with active or inactive EGPA showed no significant difference for any of the studied cytokines or chemokines.

CONCLUSIONS

No clear difference in the serum levels of measured cytokines and chemokines helped distinguish between active EGPA or inactive EGPA, or other disease or control groups.

Eosinophilia and Kidney Disease: More than Just an Incidental Finding?

Peripheral blood eosinophilia (PBE), defined as 500 eosinophils or above per microliter (µL) blood, is a condition that is not uncommon but often neglected in the management of patients with chronic kidney disease (CKD), acute kidney injury (AKI), or patients on renal replacement therapy (RRT). The nature of PBE in the context of kidney diseases is predominantly secondary or reactive and has to be distinguished from primary eosinophilic disorders. Nonetheless, the finding of persistent PBE can be a useful clue for the differential diagnosis of underdiagnosed entities and overlapping syndromes, such as eosinophilic granulomatosis with polyangiitis (EGPA), IgG4-related disease (IgG4-RD), acute interstitial nephritis (AIN), or the hypereosinophilic syndrome (HES). For patients on RRT, PBE may be an indicator for bio-incompatibility of the dialysis material, acute allograft rejection, or Strongyloides hyperinfection. In a subset of patients with EGPA, eosinophils might even be the driving force in disease pathogenesis. This improved understanding is already being used to facilitate novel therapeutic options. Mepolizumab has been licensed for the management of EGPA and is applied with the aim to abrogate the underlying immunologic process by blocking interleukin-5. The current article provides an overview of different renal pathologies that are associated with PBE. Further scientific effort is required to understand the exact role and function of eosinophils in these disorders which may pave the way to improved interdisciplinary management of such patients.

Hypereosinophilic syndrome in the differential diagnosis of pulmonary infiltrates with eosinophilia

OBJECTIVE

To describe key diagnostic considerations in patients with pulmonary infiltrates with eosinophilia, with a special emphasis on raising awareness of hypereosinophilic syndrome (HES), a disease that often involves the lungs and prompts investigation for clonal neoplastic processes that determine prognosis and treatment.

DATA SOURCES

Studies and review articles were selected from PubMed and Scopus for relevance to pertinent topics.

STUDY SELECTIONS

The literature was screened for studies that described lung eosinophilia and HES. Studies relevant to the topic were included in this review.

RESULTS

Pulmonary eosinophil infiltrates in lung biopsy specimens present a broad differential diagnosis, including eosinophilic pneumonia; hypersensitivity reactions, such as allergic bronchopulmonary fungal disease; and pulmonary manifestations of systemic diseases, such as eosinophilic granulomatosis with polyangiitis. An additional important consideration in the differential diagnosis is pulmonary involvement by HES. HES is a rare syndrome that comprises a heterogeneous group of conditions characterized by persistent blood and/or tissue eosinophilia associated with organ dysfunction. Approximately one-third of HES cases are caused by neoplastic diseases, with the remaining cases classified as reactive or idiopathic. Lung involvement is seen in up to 67% of cases and may be the presenting manifestation of the disorder.

CONCLUSION

The differential diagnosis of pulmonary eosinophilia is broad and requires a multidisciplinary approach with clinicopathologic-radiologic correlation.

Dysphonia and dyspnea in idiopathic hypereosinophilic syndrome treated with Mepolizumab

Hypereosinophilic syndrome (HES) is characterized by a persistently elevated eosinophil count associated with eosinophil-related end-organ damage and thromboembolic events, in the absence of an identifiable cause. We present a case of idiopathic HES with evidence of peripheral and tissue eosinophilia while on high dose prednisone, associated with muscle tension dysphonia, colitis, and jackhammer esophagus. The patient was treated with the interleukin-5 inhibitor, Mepolizumab, with resolution of symptoms including dyspnea, diarrhea and dysphonia.

Targeting the Interleukin-5 Pathway for Treatment of Eosinophilic Conditions Other than Asthma

Improved understanding of the contribution of eosinophils to various chronic inflammatory conditions, most notably allergic asthma, has encouraged development of monoclonal antibodies specifically targeting mediators and surface receptors involved in eosinophil expansion and activation. The pivotal role of interleukin-5 (IL-5) in eosinophil biology, its high specificity for this leukocyte subset, and its involvement in the majority of eosinophilic conditions make it a very enticing target for treatment of eosinophil-mediated disorders. Two types of antibodies have been developed to target eosinophils: antibodies against IL-5 (mepolizumab and reslizumab), and an antibody against the IL-5-receptor-alpha-chain (IL-5Rα) (benralizumab). Both types of antibodies prevent IL-5 from engaging its receptor and in addition, anti-IL-5Rα antibodies induce target-cell lysis. They have been shown to reduce circulating eosinophil counts rapidly in humans with various disorders. Herein, a brief overview of the role of IL-5 in eosinophil biology will be presented, followed by a description of the development and characteristics of antibodies targeting IL-5 or its receptor. Results of clinical trials evaluating the efficacy and safety of these new antibodies in diseases (other than eosinophilic asthma) with prominent tissue eosinophilia are reviewed, followed by safety considerations and potential future applications.

Eosinophils from Physiology to Disease: A Comprehensive Review

Despite being the second least represented granulocyte subpopulation in the circulating blood, eosinophils are receiving a growing interest from the scientific community, due to their complex pathophysiological role in a broad range of local and systemic inflammatory diseases as well as in cancer and thrombosis. Eosinophils are crucial for the control of parasitic infections, but increasing evidence suggests that they are also involved in vital defensive tasks against bacterial and viral pathogens including HIV. On the other side of the coin, eosinophil potential to provide a strong defensive response against invading microbes through the release of a large array of compounds can prove toxic to the host tissues and dysregulate haemostasis. Increasing knowledge of eosinophil biological behaviour is leading to major changes in established paradigms for the classification and diagnosis of several allergic and autoimmune diseases and has paved the way to a "golden age" of eosinophil-targeted agents. In this review, we provide a comprehensive update on the pathophysiological role of eosinophils in host defence, inflammation, and cancer and discuss potential clinical implications in light of recent therapeutic advances.

Clinical and Biological Markers in Hypereosinophilic Syndromes

Hypereosinophilic syndromes (HES) are rare, heterogeneous syndromes characterized by markedly elevated eosinophil counts in the blood and/or tissue and evidence of eosinophil-associated pathology. Although parasitic infections, drug hypersensitivity, and other disorders of defined etiology can present as HES (associated HES), treatment is directed at the underlying cause rather than the eosinophilia itself. A number of additional subtypes of HES have been described, based on clinical and laboratory features. These include (1) myeloid HES—a primary disorder of the myeloid lineage, (2) lymphocytic variant HES—eosinophilia driven by aberrant or clonal lymphocytes secreting eosinophil-promoting cytokines, (3) overlap HES—eosinophilia restricted to a single organ or organ system, (4) familial eosinophilia—a rare inherited form of HES, and (5) idiopathic HES. Since clinical manifestations, response to therapy, and prognosis all differ between HES subtypes, this review will focus on clinical and biological markers that serve as markers of disease activity in HES (excluding associated HES), including those that are likely to be useful only in specific clinical subtypes.

(A Critical Appraisal of) Classification of Hypereosinophilic Disorders

Hypereosinophilia (HE) is a heterogeneous condition that can be reported in various (namely inflammatory, allergic, infectious, or neoplastic) diseases with distinct pathophysiological pathways. In 1975, Chusid et al. published the first diagnostic criteria of hypereosinophilic syndromes (HES). Over the years, as both basic and clinical knowledge improved, several updates have been suggested, with a focus on better distinguishing isolated or asymptomatic eosinophilia from diseases with specific eosinophil-related organ damage. Moreover, underlying molecular and cellular mechanisms of eosinophilia gradually became the cornerstone of successive attempts to classify HE-related diseases. In 2011, the International Cooperative Working Group on Eosinophil Disorders criteria emerged from a multidisciplinary Working Conference on Eosinophil Disorders and Syndromes, and provided substantial contribution to the clarification of general concepts and definitions in the field of HE. Yet, owing to the low prevalence of HE/HES, to the numerous diseases encompassed in the spectrum of HE-related disorders (with sometimes overlapping phenotypes), many questions are left unanswered (e.g., the need to better standardize the use of modern molecular tools, or the clinical relevance of distinguishing different subtypes of idiopathic HES). Here, we review the current state of knowledge in the fields of classification and diagnosis criteria of HE-related diseases, with emphasis on the analysis of both strengths and weaknesses of present concepts and their usefulness in daily practice.

Optimal therapy and prospects for new medicines in eosinophilic granulomatosis with polyangiitis (Churg-Strauss syndrome)

INTRODUCTION

The prevalence of eosinophilic granulomatosis with polyangiitis (EGPA; previously known as Churg-Strauss syndrome) is lower than that of other antineutrophil cytoplasm antibody (ANCA)-associated vasculitides (AAV's), and only a few randomized controlled trials have been conducted for this rare disease. However, recent international efforts have helped delineate the best treatment approach.

AREAS COVERED

At present, EGPA conventional therapy is by default similar to that of other AAVs. Limited, non-severe EGPA can initially be treated with glucocorticoids (GCs) alone. Patients with life-threatening manifestations and/or major organ involvement must receive a combination of GCs and an immunosuppressant, mainly cyclophosphamide. Remission can be achieved in >85% of patients with these first-line treatments, but vasculitis relapses occur in more than one-third of patients, and about 85% cannot stop GC treatment because of GC-dependent asthma and/or ENT manifestations. A few biologic agents, including rituximab or mepolizumab, are now under investigation after interesting preliminary results. Expert commentary: Treatment for EGPA still has several unmet needs. Several biologic agents are now under investigation in randomized controlled trials, but a few others should be considered soon. Their benefit should be demonstrated for devising more EGPA-tailored therapeutic strategies (ideally GC-free).

Eosinophilic granulomatosis with polyangiitis in childhood: retrospective experience from a tertiary referral centre in the UK

OBJECTIVE

To describe the presenting clinical features, treatment and outcome in children with eosinophilic granulomatosis with polyangiitis (EGPA) and to define factors that predicted mortality.

METHODS

A retrospective case notes review of patients fulfilling the Chapel Hill Consensus Conference definition and/or ACR criteria for EGPA seen at Great Ormond Street Hospital, London. Demographics, clinical features, histopathology, treatment and outcomes were recorded. Descriptive statistics were expressed as median and range. Fisher's exact test was used for group comparisons. The Paediatric Vasculitis Activity Score and Paediatric Vasculitis Damage Index (PVDI) were calculated.

RESULTS

Thirteen children (38% female) aged at diagnosis 14.1 (4-15.6) years were identified. The median time to diagnosis was 2 (0-7.3) years. History of asthma was documented in 76%. The most common presenting features were pulmonary (69%), skin (61%), gastrointestinal (46%), cardiac involvement (46%), paranasal sinus abnormality (38%), arthritis/arthralgia (38%) and neurological involvement (15%). Paediatric Vasculitis Activity Score at presentation was 8/63 (2-25/63); ANCA was negative in all 10/13 patients tested. Treatment included corticosteroids in all, combined with CYC in 38% or AZA in 23%. PVDI at 12 (3-48) months follow-up was 3/72 (0-13/72). Relapses were recorded in 46%. Mortality was 15%; cardiomyopathy and PVDI scores ⩾5 significantly associated with mortality risk (P = 0.012).

CONCLUSION

EGPA in the paediatric population is a rare and potentially life-threatening vasculitis. Increased awareness is essential to secure a timely diagnosis and to promptly initiate treatment since our data emphasize a high mortality, particularly in those with cardiac involvement and significant accrued damage.

Th17 cells reflect colon submucosal pathologic changes in active eosinophilic granulomatosis with polyangiitis

BACKGROUND

Chronic eosinophilic pneumonia (CEP) or eosinophilic gastroenteritis (EG), or both, with asthma precede the onset of eosinophilic granulomatosis with polyangiitis (EGPA) in half of all EGPA patients. It is not known what determines whether patients with CEP or with EG following asthma will develop EGPA.

METHODS

We studied 17 EGPA patients and 12 patients with CEP but without EGPA. We assayed serum ICAM-1, VCAM-1, and VEGF, and the percentage of peripheral blood CD4(+) T cells producing IL-17 (Th17 cells), at both onset and remission. We also examined the numbers of submucosal eosinophils and the basement membrane-to-crypt and crypt-to-crypt distance to evaluate edema in the colon submucosa at onset and remission in EGPA and at onset in CEP.

RESULTS

Nine of 12 (75.0%) CEP patients had symptoms or endoscopic findings. Colonic submucosal eosinophil counts and edema in EGPA at onset were greater than at remission or in CEP at onset. Th17 cells (%) and serum ICAM-1 levels at onset were greater in EGPA than in CEP. In EGPA, peripheral blood Th17 cells (%) were significantly correlated with serum ICAM-1 level, colonic submucosal eosinophil count, and degree of edematous change; inversely correlated with serum VEGF level; but not correlated with VCAM-1 level.

CONCLUSIONS

Eosinophilia and colonic submucosal edematous change were greater in EGPA than in CEP. The mechanism of vasculitis in EGPA appears related to increases in serum Th17 cell numbers and ICAM-1 levels and decreases in VEGF levels.

How I treat hypereosinophilic syndromes

Hypereosinophilic syndromes (HESs) are a group of rare disorders characterized by peripheral blood eosinophilia of 1.5 × 10(9)/L or higher and evidence of end organ manifestations attributable to the eosinophilia and not otherwise explained in the clinical setting. HESs are pleomorphic in clinical presentation and can be idiopathic or associated with a variety of underlying conditions, including allergic, rheumatologic, infectious, and neoplastic disorders. Moreover, the etiology of the eosinophilia in HESs can be primary (myeloid), secondary (lymphocyte-driven), or unknown. Although corticosteroids remain the first-line therapy for most forms of HESs, the availability of an increasing number of novel therapeutic agents, including tyrosine kinase inhibitors and monoclonal antibodies, has necessarily altered the approach to treatment of HESs. This review presents an updated treatment-based approach to the classification of patients with presumed HES and discusses the roles of conventional and novel agents in the management of these patients.

Value of commonly measured laboratory tests as biomarkers of disease activity and predictors of relapse in eosinophilic granulomatosis with polyangiitis

OBJECTIVE

The aim of this study was to assess the clinical value of absolute eosinophil count, serum IgE, ESR and CRP as longitudinal biomarkers of disease activity and predictors of relapse in eosinophilic granulomatosis with polyangiitis (Churg-Strauss, EGPA).

METHODS

Patients were selected from an observational EGPA cohort. Absolute eosinophil count, IgE, ESR and CRP were measured quarterly. Disease activity was defined by validated assessment tools. The association of tests with disease activity was assessed via regression models, adjusting for repeated measures and treatment status. Survival analysis was used to determine if laboratory tests were predictive of the 3 month future flare risk.

RESULTS

Seventy-four per cent of 892 study visits in 141 patients occurred while patients were on treatment, mostly during remission or mild disease activity, defined as a BVAS for Wegener's granulomatosis (BVAS/WG) of 1 or 2. Correlations between absolute eosinophil count, IgE, ESR and CRP were mostly low or non-significant (r = -0.08 to 0.44). There were few weak associations with disease activity [absolute eosinophil count: OR) 1.01/100 U (95% CI 1.01, 1.02); ESR: OR 1.15/10 mg/l increase (95% CI 1.04, 1.27)]. When BVAS/WG ≥1 defined active disease, the absolute eosinophil count [hazard ratio (HR) 1.01/100 U (95% CI 1.01, 1.02)] was weakly predictive of flare. When BVAS/WG ≥3 defined active disease, ESR was weakly predictive of flare [HR 1.52/10 mm/h increase (95% CI 1.17, 1.67)].

CONCLUSION

The absolute eosinophil count, IgE, ESR and CRP have limitations as longitudinal biomarkers of disease activity or predictors of flare in EGPA. These findings suggest that novel biomarkers of disease activity for EGPA are needed.

Eosinophilic granulomatosis with polyangiitis (Churg-Strauss): evolutions in classification, etiopathogenesis, assessment and management

PURPOSE OF REVIEW

Eosinophilic granulomatosis with polyangiitis (EGPA) (Churg-Strauss syndrome) is a peculiar hybrid condition of a systemic antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis and a hypereosinophilic disorder with frequent lung involvement that occurs in people with asthma. This review focuses on areas of evidence or persistent uncertainty in the classification, epidemiology, clinical presentation, diagnosis, prognosis and management of EGPA and attempts to identify clues to the mechanisms in the development or course of the disease.

RECENT FINDINGS

The 2013 revision of the EGPA definition formally placed the disease in the subset of ANCA-associated vasculitides. Recently published large case series underlined that the presence of ANCAs, found in 30-40% of EGPA, determines distinct but partly overlapping disease expression and the major detrimental effect of heart involvement on survival. There is some evidence that asthma in EGPA resembles a nonallergic eosinophilic asthma phenotype. Encouraging results have been reported for the treatment of EGPA with rituximab or with the eosinophil-targeted antiinterleukin-5 agent mepolizumab.

SUMMARY

The understanding of EGPA continues to advance, but many gaps in knowledge remain. The nomenclature remains a source of conceptual variance in terms of demonstrated presence or not of vessel inflammation or ANCAs in the diagnosis of EGPA. Distinguishing EGPA from hypereosinophilic syndromes can be problematic, and an understanding of the mechanistic relation between the vasculitis and the eosinophilic proliferation is profoundly lacking. Some evidence suggests distinct disease phenotypes, but this concept has not yet been translated to phenotype-adapted therapy.

Eosinophils in vasculitis: characteristics and roles in pathogenesis

Eosinophils are multifunctional granular leukocytes that are implicated in the pathogenesis of a wide variety of disorders, including asthma, helminth infection, and rare hypereosinophilic syndromes. Although peripheral and tissue eosinophilia can be a feature of many types of small-vessel and medium-vessel vasculitis, the role of eosinophils has been best studied in eosinophilic granulomatosis with polyangiitis (EGPA), where eosinophils are a characteristic finding in all three clinical stages of the disorder. Whereas numerous studies have demonstrated an association between the presence of eosinophils and markers of eosinophil activation in the blood and tissues of patients with EGPA, the precise role of eosinophils in disease pathogenesis has been difficult to ascertain owing to the complexity of the disease process. In this regard, results of clinical trials using novel agents that specifically target eosinophils are providing the first direct evidence of a central role of eosinophils in EGPA. This Review focuses on the aspects of eosinophil biology most relevant to the pathogenesis of vasculitis and provides an update of current knowledge regarding the role of eosinophils in EGPA and other vasculitides.