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IgG4‐related disease and lymphocyte‐variant hypereosinophilic syndrome: A comparative case series

To compare the clinical and laboratory features of IgG4‐related disease (IgG4‐RD) and lymphocyte‐variant hypereosinophilic syndrome (L‐HES), two rare diseases that often present with lymphadenopathy, gastrointestinal symptoms, eosinophilia, and elevated immunoglobulins/IgE.


| INTRODUCTION
A major challenge in evaluating patients with eosinophilia is that many diseases associated with secondary, or reactive, eosinophilia are themselves difficult to diagnose. Immunoglobulin G4-related disease (IgG4-RD) is an emerging condition associated with reactive eosinophilia in one-third of patients. 1 Common clinical manifestations include dacryoadenitis, sialadenitis, lymphadenopathy, autoimmune pancreatitis, and retroperitoneal fibrosis, although nearly any organ except joints and brain parenchyma can be involved. Forty percent of patients have associated asthma or atopy, often with elevated IgE, although the eosinophilia and increased IgE appear inherent to the IgG4-RD rather than atopic disease. 1,2 Most patients have elevated serum IgG4 often accompanied by elevated total IgG and polyclonal hypergammaglobulinemia on serum protein electrophoresis. 3 Oligoclonal expansion of CD4 + T effector memory (T EM ) lymphocytes has been detected using next-generation sequencing and is thought to drive the pathophysiology and in particular the fibrosis seen in this disease. 4 Despite the protean clinical manifestations, histopathologic features from nearly any organ are similar, and diagnosis of IgG4-RD requires histologic findings including a polyclonal lymphoplasmacytic infiltrate, storiform fibrosis, obliterative phlebitis, and increased IgG4 + plasma cells. 3 Treatments for IgG4-RD include glucocorticoids and rituximab. 5 Hypereosinophilic syndromes (HES) are rare conditions characterized by chronic hypereosinophilia (eosinophils ≥1.5×10 9 /L) causing organ damage. 6 Lymphocyte-variant HES (L-HES) is a unique subtype of HES characterized by an immunophenotypically aberrant T-cell population, often with clonal T-cell receptor gene rearrangements associated with excessive Th2 cytokine production, such as interleukin (IL)-5, IL-4, and IL-13. L-HES typically affects the skin, lungs, and digestive tract, and many patients have asthma and atopic disease. 7 Laboratory features, in addition to the eosinophilia and aberrant T-cell population, include elevated IgE, polyclonal hypergammaglobulinemia, and/or small monoclonal bands on serum protein electrophoresis in some patients. The most welldescribed immunophenotype is CD3 − CD4 + , followed by CD3 + TCR α/β+ CD4 − CD8 − and CD3 + CD4 + CD7 − . 8-10 Like IgG4-RD, L-HES is commonly treated initially with glucocorticoids. 7 The natural history is generally indolent, but some patients may develop aggressive T-cell lymphoma. 11 The gold standard for diagnosis of IgG4-RD is histopathology, in keeping with the International Consensus Criteria, with corresponding clinical, laboratory, and radiological features. 12 Diagnostic criteria for L-HES are not as strictly defined as for IgG4-RD, nor are there a widely accepted set of consensus criteria, but usually involve a combination of clinical findings, hypereosinophilia, immunophenotyping, and T-cell clonality studies. 13 Given that IgG4-RD and L-HES present with overlapping clinical and laboratory features such as asthma, atopy, lymphadenopathy, eosinophilia, and elevated serum immunoglobulins, differentiating between these two rare entities is an underappreciated diagnostic challenge. 14, 15 We previously published the case of a young woman with polyclonal hyperviscosity syndrome and eosinophilia labeled as idiopathic HES, a diagnosis confirmed prior to publication by international experts in eosinophilia (case I3 in this study); 16 however, 2 years after publication, she was found to have histologically confirmed IgG4-RD. 17 Given the potential diagnostic confusion between these two entities, and the lack of large studies comparing them, we conducted a comparative case series describing the clinical and laboratory features of patients with IgG4-RD and L-HES. This is the first study to report T-cell immunophenotyping and T-cell clonality testing in a large number of patients with IgG4-RD and the first report of serum IgG4 levels in a large number of patients with L-HES.

| MATERIALS AND METHODS
Consecutive patients were retrospectively identified from the practices of author MNC (IgG4-RD) or LYC (IgG4-RD and L-HES) Jul 2008 to Jun 2015. All patient data were de-identified and unique patient numbers generated for data analysis. Forty-four patients in total were included in this study: 31 with IgG4-RD and 13 with L-HES. All patients with IgG4-RD had histologic confirmation by an expert pathologist (BFS, DFS, GWS, MS) according to the International Consensus Criteria. 12 Total IgG (Siemens © , Tarrytown, NY, USA) and IgG subclasses (IgG1, IgG2, IgG3, IgG4; Binding Site © , Birmingham, UK) were measured by nephelometry and total IgE by chemiluminescent immunoassay (Siemens Vista © ).
Patients with L-HES had clinical features in keeping with L-HES, exclusion of relevant clonal and reactive causes of eosinophilia, and aberrant T-cell immunophenotype (increased CD3 − CD4 + , CD3 + CD4 − CD8 − , or CD3 + CD4 + CD7 − ) or T-cell clonality by PCR. 9 Reference ranges for the T-cell subsets as a percentage of total lymphocytes were established in-house for investigational purposes: CD3 − CD4 + 0%-2%; CD3 + CD4 − CD8 − 2%-15%; CD3 + CD4 + CD7 − 2%-10%. Of note, for the "double-negative" CD3 + CD4 − CD8 − phenotype, the TCR αβ cells are considered the pathogenic subtype, but our flow cytometry panel did not distinguish between membrane expression of TCR αβ and TCR γδ T lymphocytes. All patients with L-HES were reviewed clinically (by LYC) and immunophenotyping of peripheral blood and/or bone marrow was reviewed (by BID). The presence of a T-cell receptor (TCR) clonal Conclusion: The overlapping features of these two diseases with divergent treatment options demonstrate the importance of familiarity with both entities to optimize diagnosis and treatment.

K E Y W O R D S
eosinophil, hypereosinophilic syndrome, hypergammaglobulinemia, IgG4, IgG4-related disease rearrangement was determined using the BIOMED-2 guidelines (see Appendix S1 for primers used). Immunophenotype was considered more important for diagnosis of L-HES than PCR. Clinical data including presenting symptoms and physical exam findings, laboratory results, pathology and radiology reports, treatment, and outcomes were collected.
Subclinical disease with objective radiologic and/or histologic findings were included as organ involvement, for example, radiographic evidence of lymphadenopathy thought to be due to IgG4-RD or L-HES, or typical computed tomography findings of IgG4-related tubulointerstitial nephritis in patients with preserved renal function.
All statistical tests were performed using SPSS software (version 13.0; SPSS Inc., Chicago, IL, USA). Group medians were compared using the Mann-Whitney U test (two independent samples, two-tailed) and proportions were compared using the chi-square test. A P value of <.05 was considered significant for all tests. The study was approved by the University of British Columbia Clinical Research Ethics Board (H15-01433) as a minimal risk study and did not require patient consent.

| Patients
Clinical data for patients with IgG4-RD and L-HES are shown in Table 1

| Organ involvement
Patients with IgG4-RD had more organs involved than those with L-HES (median 5 vs 3, P=.029). There were no differences in constitutional symptoms including weight loss, fevers, night sweats, and fatigue, although two patients with IgG4-RD had polyclonal hypergammaglobulinemic hyperviscosity syndrome. The most commonly involved organs in IgG4-RD were the submandibular glands, lymph nodes, and lacrimal glands, all of which were more frequently affected than in patients with L-HES (Table 1). In patients with L-HES, the most common symptomatic organs were skin, lungs, lymph nodes, and gastrointestinal tract; salivary and lacrimal glands were not a concern. IgG4-RD, immuglobulin G4-related disease; L-HES, lymphocyte-variant hypereosinophilic syndrome; IQR, interquartile range; SPEP, serum protein electrophoresis. a One patient had <1 g/L IgMκ, one patient had 2.8 g/L IgGλ, and one patient had <1 g/L IgGκ.

| Histopathologic features
F I G U R E 3 Baseline laboratory results of patients with IgG4-RD and L-HES. Each bar represents the proportion of patients who exceeded normal ranges of those who were tested for that parameter within each subgroup. Laboratory value ranges for these patients are shown in brackets. Units for IgG, IgG4, gamma peak: g/L; IgE: μg/L; eosinophils: giga/L; T-cell immunophenotypes: % gastrointestinal involvement; this may be due in part to patients having received corticosteroids before undergoing endoscopy and biopsy or due to other causes of such as reflux. Nine patients with IgG4-RD had bone marrow biopsies, of which only two had disease involvement with lymphoplasmacytic infiltrate, eosinophilia, and increased IgG4 + plasma cells; of note, obliterative phlebitis and storiform fibrosis (not to be confused with myelofibrosis) are not seen in bone marrow specimens and lymph node specimens. All 10 of the patients with L-HES who had bone marrow biopsies had marrow involvement with eosinophilia ( Figure 2).

| Laboratory findings
Laboratory findings are summarized in Table 2 and  Table 3.

| Treatment
Twenty

| DISCUSSION
This study is the first direct comparison of IgG4-RD and L-HES, rare diseases with significant overlapping characteristics. Both typically present in middle-aged and older adults with a slight male prepon-

derance. The variation in clinical manifestations in the patients with
IgG4-RD reflects the kaleidoscopic nature of the disease, whereas L-HES generally affects fewer target organs (Table 1)

A B
IgG4 deposits in esophageal tissue, and the investigators speculated that the biological basis of eosinophilic esophagitis and IgG4-RD may be similar. 28 Our study has a number of limitations. Tests such as computed tomography and echocardiography were not routinely performed on all patients, and thus, subclinical organ involvement may not have been detected in some patients. We were not able to measure cytokine levels such as IL-5, which might provide more insight into the mechanism(s) of the overlapping features. The cells of interest in the CD3 + 4 − 8 − phenotype are the TCR αβ , but our flow cytometry panel did not distinguish between TCR αβ and TCR γα cells. In fact, comparing L-HES to IgG4-RD also highlights the lack of widely accepted diagnostic criteria for L-HES, a rare condition wherein flow cytometry is considered the gold standard, 25 yet T-cell clonality by PCR is sometimes used as a surrogate. 29 However, the main strength of this study is that it describes for the first time the potential diagnostic overlap between these two diseases using commonly available laboratory tests

This study was funded by the Hal Kettleson Hematology Research
Fund.