Langerhans cell hyperplasia in scabies: a mimic of Langerhans cell histiocytosis

This "mite" Surprise You: Scabies Masquerading as Langerhans Cell Histiocytosis - A Case Report

Introduction

Scabies is a common parasitic infestation caused by the mite Sarcoptes scabiei. Scabies can mimic other entities clinically, resulting in misdiagnosis. The presence of a mite in the stratum corneum on biopsy specimens is diagnostic of scabies. However, there are instances when mites are not visible, and immunohistochemical (IHC) staining may be misleading. An example is when IHC demonstrates Cluster of Differentiation 1a and S100 positivity. The main differential diagnosis for this finding is Langerhans cell histiocytosis, a group of idiopathic disorders of bone marrow-derived Langerhans cells, with manifestations ranging from isolated to life-threatening multisystem disease.

Case Presentation

We present a case of a patient who was diagnosed with Langerhans cell histiocytosis based on histological findings, further review with a repeat reading and deeper sectioning of her biopsy revealed a mite in the stratum corneum, altering the diagnosis, course, and management. She subsequently developed persistent post-scabietic nodules, an underreported entity that may occur following infestation and persist for up to a year. These lesions are self-limiting and do not require repeated courses of treatment.

Conclusion

Langerhans cell hyperplasia may be seen in a multitude of entities, including scabies. Familiarity with this phenomenon is crucial to avoid unnecessary invasive investigations, aggressive management and alleviate patients' concerns.

Pseudomalignancies in Children: Histological Clues, and Pitfalls to Be Avoided

The term “pseudomalignancy” covers a large, heterogenous group of diseases characterized by a benign cellular proliferation, hyperplasia, or infiltrate that resembles a true malignancy clinically or histologically. Here, we (i) provide a non-exhaustive review of several inflammatory skin diseases and benign skin proliferations that can mimic a malignant neoplasm in children, (ii) give pathologists some helpful clues to guide their diagnosis, and (iii) highlight pitfalls to be avoided. The observation of clinical–pathological correlations is often important in this situation and can sometimes be the only means (along with careful monitoring of the disease’s clinical course) of reaching a firm diagnosis.

Langerhans cell histiocytosis: A great imitator

Langerhans cell histiocytosis (LCH) is an uncommon but serious inflammatory neoplasia that affects many organs, including the skin. Though uncommon, it should remain high on a clinician's differential diagnosis in treatment-resistant cases of conditions, such as seborrheic dermatitis, diaper dermatitis, arthropod bites, and many more. A thorough history nd physical examination for each patient can aid in the diagnosis; however, if clinically suspicious for LCH, a punch biopsy should be performed. Histologic evaluation of LCH is often enough to differentiate it from the many clinical mimickers. Characteristic findings include a histiocytic infiltrate with "coffee bean"-cleaved nuclei, rounded shape, and eosinophilic cytoplasm. Immunohistochemical stains, including CD1a, S100, and CD207 (langerin) are often needed for a definitive diagnosis. Electron microscopy also demonstrates the ultrastructural presence of Birbeck granules, but this is no longer needed due to immunohistochemical staining. Treatment is often necessary for LCH, if systemic involvement exists.

Merkel cell polyomavirus and Langerhans cell neoplasm

BACKGROUND

The relationship between various external agents such as pollen, food, and infectious agents and human sensitivity exists and is variable depending upon individual's health conditions. For example, we believe that the pathogenetic potential of the Merkel cell polyomavirus (MCPyV), the resident virus in skin, is variable and depends from the degree of individual's reactivity. MCPyV as well as Epstein-Barr virus, which are normally connected with humans under the form of subclinical infection, are thought to be involved at various degrees in several neoplastic and inflammatory diseases. In this review, we cover two types of Langerhans cell neoplasms, the Langerhans cell sarcoma (LCS) and Langerhans cell histiocytosis (LCH), represented as either neoplastic or inflammatory diseases caused by MCPyV.

METHODS

We meta-analyzed both our previous analyses, composed of quantitative PCR for MCPyV-DNA, proteomics, immunohistochemistry which construct IL-17 endocrine model and interleukin-1 (IL-1) activation loop model, and other groups' data.

RESULTS

We have shown that there were subgroups associated with the MCPyV as a causal agent in these two different neoplasms. Comparatively, LCS, distinct from the LCH, is a neoplastic lesion (or sarcoma) without presence of inflammatory granuloma frequently observed in the elderly. LCH is a proliferative disease of Langerhans-like abnormal cells which carry mutations of genes involved in the RAS/MAPK signaling pathway. We found that MCPyV may be involved in the development of LCH.

CONCLUSION

We hypothesized that a subgroup of LCS developed according the same mechanism involved in Merkel cell carcinoma pathogenesis. We proposed LCH developed from an inflammatory process that was sustained due to gene mutations. We hypothesized that MCPyV infection triggered an IL-1 activation loop that lies beneath the pathogenesis of LCH and propose a new triple-factor model.

Histopathology of Cutaneous Inflammatory Disorders in Children

Inflammatory dermatoses encompass a variety of histologic patterns that affect different portions of the skin. In spongiotic, psoriasiform, lichenoid, pityriasiform, and blistering disorders, there are predominately epidermal and junctional activities with variable superficial dermal inflammation. Hypersensitivity reactions can show either epidermal or mostly dermal changes depending on whether the exposure of the exogenous allergen occurs through an external or internal route, respectively. Exceptions include erythema multiforme and Stevens-Johnson syndrome/toxic epidermal necrolysis, where the etiology is often due to infection or ingested medications, but the histologic features are almost exclusively confined to the epidermis and dermoepidermal junction. Autoimmune disorders are unique in that lesions typically incorporate a mixture of epidermal and dermal inflammatory patterns with periadnexal inflammation, while the vast majority of vasculitis/vasculopathy and alopecia have changes limited to only the vessels and hair follicles, respectively. It is critical to recognize that a relatively limited number of histologic patterns are seen in a large array of clinical entities. Therefore, clinicopathologic correlation and careful examination of histologic details are of the utmost importance when evaluating skin biopsies for inflammatory disorders.

Langerhans Cell Histiocytosis and Langerhans Cell Sarcoma: Current Understanding and Differential Diagnosis

Langerhans cell (LC) histiocytosis (LCH) and LC sarcoma (LCS) are proliferative processes consisting of cells having morphologic and phenotypic features of Langerhans cells (LCs), although the latter may have lost some of these features. Because neoplastic nature of LCH as well as LCS is more likely by recent studies, a category of LC hyperplasia can be better characterized. LCH and LCS are rarely seen in daily pathology practice, but it is important to accurately characterize these lesions. For this purpose, an outline covering proliferations of LC and related cells was constructed. The scheme of this outline is based especially on evaluating borderline lesions, neoplastic trans-differentiation, and degree of similarity with the normal counter-parts. In addition, the organization and update of the current classification scheme for histiocytic and dendritic-cell proliferations is presented.

Langerhans cell histiocytosis: a comprehensive review

Langerhans cell histiocytosis (LCH) is currently regarded as a myeloid neoplasm, with remarkably broad clinical spectrum, ranging from isolated skin or bone lesions to a disseminated disease that can involve nearly any organ. LCH is generally regarded as a sporadic disease that occurs predominantly in the paediatric population. The diagnosis of LCH is confirmed by immunohistochemistry (IHC) by demonstrating the presence of dendritic cell markers such as S100 protein, in addition to CD1a and langerin. Contrary to previous beliefs, recent literature reveals that the pathogenesis of LCH might involve a clonal process implicating BRAF c.1799T>A (p.Val600Glu) and other mutations [(600DLAT) B-RAF and (T599A) B-RAF, somatic MAP2K1 mutations].Through this review article, we have summarised the latest understanding of the biological and salient histological characteristics of LCH and its potential morphological mimics.

Immunohistochemistry in dermatopathology

CONTEXT

Immunohistochemistry is not a diagnostic test but a highly valuable tool that requires interpretation within a context.

OBJECTIVE

To review the current status and limitations of immunohistochemistry in dermatopathology.

DATA SOURCES

English-language literature published between 1980 and 2014.

CONCLUSIONS

Although immunohistochemistry is rarely completely specific or sensitive, it is an important adjunctive technique in dermatopathology and can be helpful in a series of diagnostic dilemmas.

Interleukin-1 loop model for pathogenesis of Langerhans cell histiocytosis

We propose Langerhans cell histiocytosis (LCH) is an inflammatory process that is prolonged by mutations. We hypothesize that Merkel cell polyomavirus (MCPyV) infection triggers an interleukin-1 (IL-1) activation loop that underlies the pathogenesis of LCH. Langerhans cells (LCs) are antigen presenting cells in the skin. When LCs encounter exogenous antigens, they migrate from the epidermis into draining lymphoid tissues to initiate T-cell activity. It has been proposed that LC migration-related factors, including E-cadherin, matrix metalloproteinase, and Notch ligand induce LCH activity. We found that the tyrosine phosphatase SHP-1, which binds IL-1 receptor-associated kinase 1, is expressed at a significantly higher level in LCH affecting multiple organ systems (MS-LCH) than in LCH affecting a single organ system (SS-LCH). IL-1 stimulates T helper 17 cells and their signature cytokine IL-17 had been a matter of controversy. We detected higher levels of IL-17A receptor expression in MS-LCH than in SS-LCH and proposed an IL-17 endocrine model that could settle the controversy. IL-1 is the first cytokine secreted in response to sensitizers and promotes LC migration from sentinel tissues. Myeloid differentiation primary response 88 (MyD88), downstream of the IL-1 receptor, has functions in both RAS signaling and inflammation, leading to human cell transformation. In 2010, an activating mutation in the B-rapidly accelerated fibrosarcoma gene (BRAF) V600E was found in LCH. This BRAF mutation induces phosphorylation of the extracellular signal-regulated kinase (ERK) that may play an important role with MyD88 in LCH pathogenesis. However, phosphorylated ERK (pERK) is rapidly dephosphorylated by dual specificity phosphatase 6 (DUSP6), and limited proliferation is predicted in BRAF mutant cells. MyD88 binds pERK via its D-domain, thereby preventing pERK-DUSP6 interaction and maintaining ERK in an active, phosphorylated state. We detected MCPyV-DNA in the peripheral blood cells of two out of three patients with LCH in high-risk organs but not in those of patients with LCH in non-high-risk organs (0/12; P = .029). MCPyV infection can trigger precursor LCH cells with BRAF mutation to produce IL-1; the IL-1 loop is amplified in all LCH subclasses. Our model indicates both BRAF mutation and IL-1 loop regulation as potential therapeutic targets.

Intestinal Langerhans cell histiocytosis-like lesion in an adult presented with diverticulitis: a reactive or neoplastic condition?

The involvement of the gut by Langerhans cell histiocytosis (LCH) is very rare in adults; however this is usually observed with a disseminated disease in children. We report a 75-year-old male patient who underwent right hemicolectomy for a complicated intestinal diverticular disease. The surgical specimen revealed LCH-like proliferative lesion associated with diverticulitis. The overall morphological and immunohistochemical findings are indistinguishable from LCH. Systemic scans and subsequently performed bone marrow biopsies were free of disease. Although the HUMARA clonality assay cannot be assessed, the lack of evidence of LCH progression or disease elsewhere in the whole body strongly supported the possibility of an atypical reactive phenomenon probably due to the underlying intestinal diverticular disease. Therefore, it is important to avoid diagnosing such a unifocal Langerhans cell proliferation as LCH in patients with underlying pathologies in the absence of systemic involvement. Therefore, without knowledge of clonal status of a unifocal Langerhans cell proliferation, we recommend using the terminology of LCH-like lesion.

Langerhans cell hyperplasia of the skin mimicking Langerhans cell histiocytosis: a report of two cases in children not associated with scabies

Langerhans cells histiocytosis (LCH) affecting the skin most commonly has clinical and histopathologic diagnostic features. We are reporting two examples of Langerhans cell (LC) hyperplasia recognized in the skin biopsies of two children initially interpreted as LCH. The first was an 8-year-old boy finally interpreted as having an atypical type of contact dermatitis, while the second, an 8-year-old girl, was assumed to have Pytiriasis lichenoides et varioliformis acuta. None showed evidences of scabies. Both presented spongiotic dermatitis with numerous CD1a+ cells. As more cases of LC hyperplasia are recognized, new details emerge helping in the differential diagnosis. Strict clinical-pathologic correlation is suggested in order to avoid misdiagnosis.

Intradural dirofilariasis mimicking a Langerhans cell histiocytosis tumor

We report the case of a 6-year-old female who presented a cervical intradural extra-spinal tumor, initially considered as a Langerhans cell histiocytosis. Additional histological slides revealed a Dirofilaria repens dirofilariasis. The particularity of this case is the intradural location of this filariasis, which usually has a subcutaneous or conjunctival location in human.