A case report of multicentric reticulohistiocytosis with atypical cutaneous presentation.

Multicentric reticulohistiocytosis (MRH) is a rare systemic disorder characterized by histiocytic hyperplasia that mainly involves the skin, mucous membranes, and joints. The typical clinical features include papules, nodules, and arthritis. MRH lesions are relatively extensive but small and scattered. Joint inflammation is characterized by diffuse symmetric polyarthritis as the first symptom, which can be severe and disabling due to destructive joint changes. MRH is easily misdiagnosed in clinical practice. Here, we report the case of an elderly male patient who presented with polyarticular pain in the hip and interphalangeal joints as the first manifestation, followed by the development of large, isolated, bulging skin nodules, which are atypical MRH lesions. This is rare in all MRH case reports, and we made the correct diagnosis by combining skin histopathology, immunohistochemistry, and other clinical examinations. We performed surgical treatment on the local skin lesions of this patient. This case suggests that clinicians should actively correlate the condition and accurately diagnose MRH when encountering atypical skin changes or other diseases as the first symptom and explore the mechanisms of MRH and other clinical manifestations.

Utility of 18F-FDG PET/CT in Assessment of Disease Extent and Response to Treatment in Xanthoma Disseminatum.

The clinical utility of 18F-FDG PET/CT is being increasingly recognized in histiocytic disorders. We report the case of a 23-y-old woman who presented with slowly progressive, yellowish-brown papules, plaques, and nodules over her face and flexures. Besides the multiple cutaneous lesions, lesions of the brain, stomach, gallbladder, and marrow were additionally revealed by baseline 18F-FDG PET/CT. Skin biopsy and the overall clinical picture were consistent with xanthoma disseminatum. Subsequent PET/CT after cladribine therapy revealed a decrease in the extent and metabolic activity of most lesions, suggestive of a favorable response. This case report highlights the potential role of 18F-FDG PET/CT in the accurate assessment of disease extent and posttreatment response in rare histiocytic disorders.

Multicentric Reticulohistiocytosis (Mrh): A Case Report On A Rare Destructive Arthritis.

Multicentric Reticulohistiocytosis is a rare disorder of unknown aetiology which affects skin and joints predominantly. There are no specific laboratory investigations for diagnosis. Diagnosis can be made clinically and on a histopathological basis. There is no consensus on treatment. We report a case from Pakistan with classical presentation who did well on methotrexate and low dose steroids. Prompt diagnosis and early treatment may save from significant disability.

Reddish-brown, papulonodular skin lesions in the periungual region.

Multicentric reticulohistiocytosis is a rare, non-Langerhans cell histiocytosis that most commonly presents in women in their fourth or fifth decades of life. Cutaneous involvement, characterized by reddish-brown papules in a "string of pearls" or "coral bead" linear formation, and joint involvement are the two most common manifestations at presentation. Histopathology demonstrates dermal proliferation of epithelioid histiocytic-appearing cells with ground glass cytoplasm. We report a 51-year-old woman who presented with ruddy, periungual papules and bilateral joint pain in the hands, consistent with multicentric reticulohistiocytosis. We describe the clinical and histopathologic presentation, therapeutic options, and differential diagnosis of this rare condition.

Novel ANKRD26 and PDGFRB gene mutations in pediatric case of non-Langerhans cell histiocytosis: Case report and literature review.

Cutaneous non-Langerhans cell histiocytosis (NLCH) is a rare and biologically benign entity that can be broadly classified into two categories: xanthogranuloma and non-xanthogranuloma. The xanthogranuloma family is characterized by a proliferation of histiocytes with both macrophage and dendritic cell differentiation, negative BRAF mutation, and rare Touton-type giant cells. Molecular studies have reported that mutations involved in the MAPK signaling pathways are implicated in the pathophysiology of histiocytoses. While LCH is associated with the somatic mutation of BRAF v600e, however, mutations and gene fusions in NLCH cases are undefined. We hereby present a 19-month-old female with recalcitrant nodular rashes diagnosed as NLCH with associated novel genetic mutation involving ANKRD26 and PDGFRB genes, as well as PDGFRB::CD74 fusion mRNA. Immunohistochemical staining showed strong and diffuse CD68 and CD163 positivity, and negative CD1a, CD207, ALK D5F3, S100 protein, and BRAF V600E (VE1). Albeit unknown significance, this case of an ANKRD26 and PDGFRB gene mutation in cutaneous NLCH has not been reported prior in the literature. Our case highlights the advantage of pathology and genetic studies in cutaneous NLCH to increase the understanding of this heterogeneous enigmatic disorder and identify further options in management.

Clinical characteristics of multicentric reticulohistiocytosis and distinguished features from rheumatoid arthritis: a single-center experience in China.

OBJECTIVE: To investigate the clinical features of multicentric reticulohistiocytosis (MRH). METHODS: The clinical manifestations, laboratory examination results and histologic characteristics of eleven patients with MRH were collected and compared with those of 33 patients with rheumatoid arthritis. RESULTS: In total, 72.7% of the MRH patients were women. The median age was 46 years (range 33-84 years). Diagnosed by specific pathologic features, all MRH patients exhibited cutaneous involvement. The dorsa of the hands, arms, face and auricle were the most commonly affected areas. Nodules were also located on the legs, scalp, trunk, neck, and even the hypoglossis and buccal mucosa. Ten MRH patients (90.9%) had symmetric polyarthritis. Compared with rheumatoid arthritis (RA) patients, MRH patients were more likely to have distal interphalangeal joint (DIP) involvement (63.6% vs 24.2%, P = 0.017) and less likely to have elbow (36.4% vs 72.7%, P = 0.003), ankle (45.5% vs 93.9%, P < 0.001) and metacarpophalangeal joint (MCP) (36.4% vs 78.8%, P = 0.009) involvement. Positivity for rheumatoid factor (RF) (36.4% vs 84.6%, P = 0.001) and anti-CCP antibody (9.1% vs 81.8%, P = 0.000), as well as the median RF titer [43.8 (31.7-61.0) vs 175.4 (21.3-940.3), P = 0.021], in MRH patients was lower than in RA patients. Elevation of the erythrocyte sedimentation rate (ESR) was also less common in MRH patients than in RA patients (36.4% vs 72.7%, P = 0.030). After treatment with median- to large-dose corticosteroids and disease-modifying antirheumatic drugs, 8 patients achieved complete remission and 2 patients partial remission (skin lesions ameliorated, joint lesions not ameliorated). CONCLUSION: Always pathologically diagnosed, MRH is a systemic disease involving RA-like erosive polyarthritis and a specific distribution of skin nodules characterized by "coral beads". More DIP involvement and less elbow, ankle and MCP involvement are seen in MRH than in RA. In addition, less positivity and lower-titer RF, uncommon presence of anti-CCP antibodies and ESR elevation may be helpful to distinguish MRH from RA.

A novel GAB2::BRAF fusion in cutaneous non-Langerhans-cell histiocytosis with systemic involvement.

Several mutations and gene fusions involved in the mitogen-activated protein kinase (MAPK) pathway have been reported in histiocytic neoplasms including Langerhans cell histiocytosis and non-Langerhans-cell histiocytosis (NLCH). We identified a GAB2::BRAF fusion in a cutaneous lesion from a 22-year-old woman who presented with central diabetes insipidus and red/brown papules on her face, oral mucosa, axilla, and groin. Skin biopsy showed a CD68+, S100-, and CD1a- histiocytic proliferation consistent with NLCH, best clinically classified as xanthoma disseminatum. Next-generation sequencing identified a GAB2::BRAF fusion involving exon 2 of GAB and exon 10 of BRAF. This case implicates a novel fusion in the MAPK signaling pathway, not previously reported in histiocytic neoplasms, as a possible driver of NLCH. Our findings underscore the utility of performing molecular studies on skin biopsy specimens with NLCH to help identify potential targets for therapy.

Generalized Eruptive Histiocytoma With S100 Protein-Positive Histiocytes and Prominent Eosinophilic Infiltration: A Rare Case Report.

ABSTRACT: Generalized eruptive histiocytoma (GEH) is a very rare benign disorder belonging to the group of non-Langerhans cell histiocytosis (non-LCH). GEH is characterized by a nearly uniform infiltrate of histiocytes with classic immunological phenotype (CD68+, S-100- and CD1a-). Prominent eosinophilic infiltration and S100-positive histiocytes are rarely associated in GEH. In this article, we reported a middle-age man presented with disseminated reddish papules distributed on the trunk and proximal extremities. A skin biopsy of the papule showed a dense histiocytic infiltration with prominent eosinophils. By immunohistochemistry, the histiocytes revealed strongly positive for CD68 and S100 protein and negative for CD1a and Langerin (CD207). Based on clinical and histopathological criteria, the diagnosis of GEH was established. We presented this rare case of GEH with such distinctive features to strengthen the awareness of this uncommon form of non-LCH. Classical histopathological and immunological features cannot reliably distinguish GEH from other non-LCH.

An Atypical Myelomonocytic Cell Infiltrate: Use of Next-Generation Sequencing to Diagnose Indeterminate Cell Histiocytosis.

ABSTRACT: Indeterminant cell histiocytosis (ICH) is a rare lymphoproliferative disorder that demonstrates features of Langerhans and non-Langerhans cell histiocytoses and diagnosis can be challenging. We present a case of a 62 year old woman with a generalized eruption of erythematous papules on the face, trunk and extremities. Skin biopsies demonstrated a dermal mononuclear cell infiltrate with monocytic (CD4, CD33), histiocytic (CD68, CD163), and dendritic cell (CD1a) immunophenotype but negative for Langerhans' cell marker (CD207). The differential diagnosis included leukemia cutis and ICH, and further workup revealed a normal bone marrow biopsy. To confirm the diagnosis of ICH, next generation sequencing with ETV3-NCOA2 gene fusion was performed and was positive. The patient's condition improved with methotrexate and narrow band UVB phototherapy. Our case adds to the existing literature supporting the use of next-generation sequencing to test for ETV3-NCOA2 gene fusion in suspected cases of ICH.

Role of FDG PET/CT in the Evaluation of Therapy Response in Systemic Juvenile Xanthogranuloma.

ABSTRACT: Juvenile xanthogranuloma, a rare type of non-Langerhans cell histiocytosis, is mostly seen in childhood and adolescence and generally manifests as widespread skin lesions. It rarely shows systemic involvement. Although the cutaneous form is often self-limited, systemic form is quite aggressive. Here we report the findings of FDG PET/CT scans during the course of cladribine therapy in a 6-year-old girl with systemic juvenile xanthogranuloma.

Multicentric reticulohistiocytosis with dermatomyositis-like features: A case report with dermoscopy and reflectance confocal microscopy findings.

Multicentric reticulohistiocytosis (MRH) is an insidious-onset, non-Langerhans-cell histiocytosis (NLCH) affecting the joints and skin. Early diagnosis is important to prevent destructive arthritis and disease-related complications. Reflectance confocal microscopy (RCM) is a technique that allows the visualization of the epidermis and superficial dermis noninvasively on a horizontal plane with quasi-histologic images of the skin. RCM features of NLCH including Rosai-Dorfman disease, adult xanthogranuloma (AXG), and juvenile xanthogranuloma (JXG) have been reported. However, RCM features of MRH have not been described previously. Here we present the RCM features of a case of MRH with dermoscopic and histopathologic features.

Letter to Editor: Characterizing the Lack of Specificity of the Histopathological Findings Seen in Multicentric Reticulohistiocytosis and Reticulohistiocytoma.

Both reticulohistiocytoma and multicentric reticulohistiocytosis are defined by their shared histopathologic appearance of dermal proliferations of mononuclear histiocytes and multinucleated giant cells with eosinophilic "ground-glass" or "two-toned" cytoplasm. To assess the specificity of the histopathologic findings seen in reticulohistiocytoma and reticulohistiocytosis, this study retrospectively examined 109 random, unscreened excision specimens of ruptured cysts to determine at what frequency "ground-glass" or "two-toned" histiocytes and multinucleated giant cells are seen in reactive cutaneous infiltrates. Slightly more than half (56.9%) of the ruptured cyst cases had "ground-glass" histiocytes. The majority (84%) of the ruptured cyst cases had multinucleated giant cells. The shared histologic findings associated with reticulohistiocytoma and reticulohistiocytosis are much more pervasive than previously documented and are relatively non-specific. Identification of immunohistochemical and/or molecular biomarkers that distinguish reticulohistiocytoma and reticulohistiocytosis from histologic mimickers would likely prove indispensable.

Multicentric reticulohistiocytosis masquerading as cutaneous connective tissue disease.

Multicentric reticulohistiocytosis (MRH) is a rare type of non-Langerhans cell histiocytosis characterized by coral-toned papules with predilection for dorsal surfaces in addition to severe arthropathy. It sometimes proves difficult to differentiate these joint and skin findings clinically from certain rheumatologic diseases, primarily dermatomyositis. Herein, we present an 82-year-old woman who presented with the clinical findings described above and was subsequently diagnosed with MRH after biopsy and review of relevant clinical history. Because about 25% of patients diagnosed with MRH have an underlying occult malignancy, our patient underwent a complete malignancy workup that was negative. She was treated with systemic corticosteroids and methotrexate, which resulted in an improvement of the arthritis and constitutional symptoms. This case demonstrates that in patients with both rheumatologic and dermatologic symptoms, particularly on acral surfaces, MRH must be a diagnostic consideration. Identifying this disease early in its course can prevent negative consequences for the patients, specifically arthritis mutilans and upper airway involvement.

Progressive nodular histiocytosis: an unusual disorder.

Progressive nodular histiocytosis (PNH) is a rare type of non-Langerhans cell histiocytosis of the xanthogranuloma group. Less than 20 cases have been reported. We report here a novel case of PNH with dermoscopic description and post-surgical outcome. Our patient presented with pruritic papules and nodules with progression over two years. Dermoscopic examination of large lesions showed multiple telangiectases without ulceration. There was no mucosal involvement. Histopathological analysis of a papule showed a dermal infiltrate composed of histiocytes and many Touton giant cells; a nodule revealed a dermis occupied by spindle cells arranged in a storiform pattern. The nodules were resected and the largest surgical defect, on the forehead, was corrected with A-T advancement flap. The papules were treated with cryosurgery achieving adequate cosmetic outcome without recurrence.

Case Report: Multicentric Reticulohistiocytosis Associated With Posterior Mediastinal Adenosquamous Carcinoma, Antinuclear Antibody Positivity and Lupus Anticoagulant Positivity.

Multicentric reticulohistiocytosis (MRH) is a rare systemic disease of non-Langerhans cell histiocytosis. A number of studies in the literature have documented that it can coexist with malignancy or autoimmune disease, making it difficult to determine the most appropriate therapy. Here, we present a case study of MRH associated with posterior mediastinal adenosquamous carcinoma along with antinuclear antibody positivity and lupus anticoagulant positivity. The patient experienced 6 months of clinical benefit after surgical resection and chemoradiotherapy of the mediastinal malignancy. This case adds to the available literature on multicentric reticulohistiocytosis associated with different types of malignancy and provides supplementary clinical data on the coexistence of this syndrome with malignancy and immune system abnormalities. To the best of our knowledge, this is the first case study describing MRH accompanied by posterior mediastinal adenosquamous carcinoma and lupus anticoagulant positivity. The unknown aetiology and polymorphic clinical presentation of MRH warrants further investigation.