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Background: Xanthogranulomatous osteomyelitis (XO) is a rare disease characterized radiologically by an osteolytic lesion with cortical expansion or disruption. Differentiating this condition from other osteolytic diseases such as primary or metastatic bone neoplasms is imperative. Several case reports have been published on XO, with previous reports predominantly identifying bacteria such as Pseudomonas or Staphylococcus as causative organisms. However, fungal infection-induced XO has not yet been reported. Case presentation: We present the case of a 23-year-old woman with a tumor-like osteolytic lesion in the pubic bone. The patient had experienced pelvic pain and intermittent febrile episodes for 2 months. Plain radiography revealed an osteolytic lesion in the right pubic tubercle. Magnetic resonance imaging suggested a cystic bone tumor or tubercular infection. Surgical intervention included curettage of the lesion and irrigation with normal saline. Histopathological examination of the specimen revealed abundant foamy histiocytes with inflammatory infiltrates consistent with XO. Culture of the osteolytic lesion confirmed an Aspergillus species infection and antifungal treatment was initiated. At 1-year follow-up, no evidence of local recurrence was observed. Conclusions: Although rare, XO requires differentiation from similar conditions and is treated with surgical intervention and targeted medical therapy based on the identified organisms. Clinicians should be mindful that XO can also be induced by fungal infections and that combination antifungal treatments may be beneficial in such cases. [ABSTRACT FROM AUTHOR]

Feline histiocytic diseases are uncommon and rarely reported. Feline progressive histiocytosis (FPH) is the most common histiocytic disease in cats, predominantly affecting middle-aged animals. The most common presentation is the cutaneous form with solitary or multiple cutaneous nodules. A female, mixed-breed 6-year-old cat was presented with a 9-month history of a nodule in the nasal planum and was diagnosed by histopathology with histiocytic proliferation. At the time of diagnosis, new nodules were discovered on the lower lip, digit, and two lesions in the tail region, with the largest measuring 1.5 cm. Supplementary immunohistochemistry, showed immunolabeling for Iba-1 that in combination with the clinical course of the disease, confirmed the diagnosis of FPH. No response to chemotherapy treatment with lomustine alternated with doxorubicin was achieved. Toceranib phosphate resulted in a transient response and, stable disease for a short period (6 weeks). Electrochemotherapy with bleomycin was initiated and resulted in partial remission. Later on, chlorambucil was also started. Ultimately, the combination of all three treatments led to a complete response and disappearance of all the lesions. FPH is considered a disease resistant to various treatments, and effective treatments have not been reported. In this case report, we describe a successful multimodal therapeutic approach that resulted in complete resolution of the FPH and long-term survival (460 days without external lesions at the time of death). Further studies are necessary to confirm the efficacy of this therapeutic approach. [ABSTRACT FROM AUTHOR]

Abstract Background Xanthogranulomatous osteomyelitis (XO) is a rare disease characterized radiologically by an osteolytic lesion with cortical expansion or disruption. Differentiating this condition from other osteolytic diseases such as primary or metastatic bone neoplasms is imperative. Several case reports have been published on XO, with previous reports predominantly identifying bacteria such as Pseudomonas or Staphylococcus as causative organisms. However, fungal infection-induced XO has not yet been reported. Case presentation We present the case of a 23-year-old woman with a tumor-like osteolytic lesion in the pubic bone. The patient had experienced pelvic pain and intermittent febrile episodes for 2 months. Plain radiography revealed an osteolytic lesion in the right pubic tubercle. Magnetic resonance imaging suggested a cystic bone tumor or tubercular infection. Surgical intervention included curettage of the lesion and irrigation with normal saline. Histopathological examination of the specimen revealed abundant foamy histiocytes with inflammatory infiltrates consistent with XO. Culture of the osteolytic lesion confirmed an Aspergillus species infection and antifungal treatment was initiated. At 1-year follow-up, no evidence of local recurrence was observed. Conclusions Although rare, XO requires differentiation from similar conditions and is treated with surgical intervention and targeted medical therapy based on the identified organisms. Clinicians should be mindful that XO can also be induced by fungal infections and that combination antifungal treatments may be beneficial in such cases.

This article discusses a case of normolipemic xanthoma associated with folliculotropic mycosis fungoides (fMF), a variant of mycosis fungoides. The patient, a 60-year-old Japanese man, presented with yellowish masses and patchy alopecia on the scalp, as well as follicular papules on the trunk and extremities. Trichoscopy and histological analysis revealed mucin deposition, lymphocyte and eosinophil infiltrations, and dense infiltration of histiocytes mixed with eosinophils and lymphocytes. The article suggests that the tumour microenvironment triggers histiocyte infiltration, which may lead to xanthoma formation. The case highlights the challenges in diagnosing fMF due to excessive granulomatous/xanthomatous components and emphasizes the importance of a comprehensive assessment for a definitive diagnosis. [Extracted from the article]

We report a histiocytic sarcoma originating from the epididymis observed in a 110-week-old male CD-1 mouse in a carcinogenicity study. At necropsy, no lesions were observed in the epididymis. Histologically, a neoplastic lesion was observed in the cauda of the epididymis that was well demarcated from the surrounding tissues. The lesion mainly consisted of spindle-shaped tumor cells with oval to elongated nuclei and abundant eosinophilic or foamy cytoplasm. The tumor cells were arranged in a fascicular pattern, interlacing bundles, or a whorl pattern. The nuclei showed mild atypia with irregular shapes and varied sizes, whereas few mitotic figures and no typical multinucleated cells were observed. The epididymal ducts remained within the neoplastic lesion, and the tumor cells invaded between the epithelium and the smooth muscle layer of the epididymal duct. Immunohistochemically, the tumor cells were positive for vimentin and macrophage markers (Iba1, CD204, F4/80, and Mac-2) but negative for cytokeratin and other mesenchymal cell (a-smooth muscle actin, desmin, CD31, and platelet-derived growth factor receptor-ß), neural cell (S-100 and nestin), or Leydig cell markers (calretinin). Proliferating cell nuclear antigen-positive tumor cells were sporadically observed in the lesion. Based on these results, the tumor was diagnosed as a histiocytic sarcoma originating from the epididymis. This report provides additional histopathological evidence of spontaneous histiocytic sarcomas originating from the epididymis of aged mice. [ABSTRACT FROM AUTHOR]

Simple Summary: Erdheim–Chester disease (ECD) is a rare, non-Langerhans cell histiocytic disease, characterized as a clonal hematopoietic malignancy in 2016. MAP kinase and PI3K-AKT pathway somatic mutations and/or fusion genes play significant roles in disease pathogenesis. These mutations now shape the landscape of targetable treatment options for this patient population. Additionally, previous research has shown that patients with ECD have a higher frequency of concomitant myeloid neoplasms as well as mutations traditionally related to clonal hematopoiesis detected in peripheral monocytes. The goals of this study are to examine treatment outcomes with the use of small molecule inhibitors versus conventional therapy in ECD over a longitudinal period. We also aim to identify relevant trends in laboratory parameters, specifically peripheral blood monocytes, that may offer insight into the mechanisms driving disease progression. A retrospective analysis of 20 adult patients with histopathological and clinical diagnoses of ECD was conducted at a single institution over a twenty-year period (2002–2022). Clinical responses were compared on the basis of treatments rendered, which included chemotherapy, immunotherapy, systemic corticosteroids, surgery and radiation, or targeted agents, referring to any small molecular inhibitors. Treatment response evaluation varied by the anatomic site(s) of disease, the extent of disease at diagnosis, and the imaging modality employed. In this analysis, patients were treated with a combination of targeted agents, myelosuppressive therapies, and radiation at various points in their disease courses. Of these, the most common treatment modality rendered was targeted therapy, employed in 11 of 20 patients. Partial responses or better were observed in 15 of 20 patients. Rates of stable disease trended towards being more frequent with targeted therapy versus conventional therapy but did not reach significance (p = 0.2967). Complete response rates trended towards being more common with conventional therapy than molecular (p = 0.5) but were equivocal overall. Trends of peripheral blood absolute monocytes with relation to disease activity were reviewed as recent literature implied that monocyte levels surrounding disease progression were of potential prognostic significance in histiocytic diseases. Amongst the patients who progressed at any point during their treatment course, absolute monocyte count (in K/µL) was identified at the closest available timepoint prior to or following disease progression and at the lowest value (nadir) following re-institution of therapy prior to any additional agent(s) being employed. There was no statistically significant difference in either of these monocyte values nor in disease outcomes with respect to treatments rendered within our cohort. However, our cohort consists of a heterogenous population of patients with ECD with data that highlights several trends over a longitudinal period, spanning the advent of targeted therapy. Significant differences are anticipated in ongoing analyses. [ABSTRACT FROM AUTHOR]

Feline histiocytic diseases are uncommon and rarely reported. Feline progressive histiocytosis (FPH) is the most common histiocytic disease in cats, predominantly affecting middle-aged animals. The most common presentation is the cutaneous form with solitary or multiple cutaneous nodules. A female, mixed-breed 6-year-old cat was presented with a 9-month history of a nodule in the nasal planum and was diagnosed by histopathology with histiocytic proliferation. At the time of diagnosis, new nodules were discovered on the lower lip, digit, and two lesions in the tail region, with the largest measuring 1.5 cm. Supplementary immunohistochemistry, showed immunolabeling for Iba-1 that in combination with the clinical course of the disease, confirmed the diagnosis of FPH. No response to chemotherapy treatment with lomustine alternated with doxorubicin was achieved. Toceranib phosphate resulted in a transient response and, stable disease for a short period (6 weeks). Electrochemotherapy with bleomycin was initiated and resulted in partial remission. Later on, chlorambucil was also started. Ultimately, the combination of all three treatments led to a complete response and disappearance of all the lesions. FPH is considered a disease resistant to various treatments, and effective treatments have not been reported. In this case report, we describe a successful multimodal therapeutic approach that resulted in complete resolution of the FPH and long-term survival (460 days without external lesions at the time of death). Further studies are necessary to confirm the efficacy of this therapeutic approach.

Rosai Dorfman disease (RDD) is a non-Langerhans cell histiocytic neoplasm characterized by sinus histiocytosis with variable emperipolesis. There is a limited understanding of the factors that contribute to disease progression. Traditional management of RDD consists of local therapies (resection, radiation) for localized disease and myelosuppression for systemic disease; targeted medications have also recently been introduced into clinical practice as an additional therapeutic modality. The goals of this study are to compare the impact of targeted therapies to conventional management of RDD and identify trends in laboratory data that may provide insight into disease progression. A retrospective analysis was conducted at a single institution over a 20-year period in 35 adult patients with histopathologic evidence of RDD without confounding secondary malignancies. Clinical data points included laboratory evaluation, molecular diagnostics, imaging, and therapies rendered. Binary data was utilized for statistical analysis and comparison of outcomes by treatment type and utilization of targeted agents. Evaluation of treatment response varied based on anatomic disease sites and baseline imaging modality. To standardize the radiographic analysis, we included PERCIST (if PET was utilized) or RECIST assessments (in the cases of CT or MR imaging). Conventional therapies rendered included local treatment (surgery, radiation, intralesional injections), systemic corticosteroids, immunotherapy, and chemotherapy while targeted agents included only small molecule inhibitors. In this analysis, primary disease was identified in cutaneous, osseous, and CNS structures (17, 11, and 6/35 patients respectively). Management consisted of surgery (12/35 patients), steroid and myelosuppressive therapies (9/35 each), immunotherapy (5/35), and targeted molecular agents (5/35). In evaluating outcomes, the proportion of partial responses was substantially higher in recipients of molecular as compared to conventional therapy (4/5 patients compared to 6/29) while complete responses were more common in the conventional therapy cohort (12/29 compared to 1/5). Lastly, an evaluation of peripheral blood absolute monocytes in all patients who had progressed on therapy identified a significant decrease in pre-progression values as compared to values following therapy re-institution (averages of 0.70 and 0.27 K/µL, respectively; p = 0.0002, 95% CI 0.652–0.2360). Larger-scale studies are needed to further evaluate the relevance of the monocyte trends that were identified in terms of their relationship to disease status. This study is the largest analysis of Rosai Dorfman disease, that we are aware of, from a single institution. In this cohort, the utilization of small molecule inhibitors corresponded to a greater increase in partial responses than conventional therapies, although the opposite effect has been observed in complete responses. This finding can be attributed to the recent introduction of targeted agents and shorter follow-up. We anticipate higher complete response rates with the use of small molecule in ongoing analyses over a longer follow-up period. The recognition of relative monocyte elevation prior to disease progression is an intriguing and to our knowledge, novel finding in the field of Rosai Dorfman disease. Future studies aimed at elucidating the implications of this trend are in progress. [ABSTRACT FROM AUTHOR]

Feline pulmonary Langerhans cell histiocytosis (FPLCH) is a rare histiocytic proliferative disease of middle‐aged to older domestic cats. Langerhans cells in the terminal airways proliferate and infiltrate the interstitium and the airways to a lesser degree, widely effacing normal parenchyma. Historically, definitive diagnosis has required postmortem evaluation where pulmonary lesions have a classic gross and histologic morphology. Here, we present the first documented antemortem diagnosis of FPLCH using bronchoalveolar lavage (BAL) cytology and immunocytochemistry (ICC) in a 9‐year‐old British shorthair mix. The cat had a 3‐month history of respiratory difficulty that was refractory to steroids and antimicrobials. Pulmonary radiographs had marked diffuse changes with a complex bronchointerstitial and micronodular pattern. BAL cytology revealed neutrophilic inflammation and markedly increased histiocytes with morphology distinct from typical pulmonary macrophages. ICC characterized histiocytes as CD1a+/E‐cadherin+/CD11b−/PanCK−, consistent with a Langerhans cell phenotype. The cat was humanely euthanized due to poor prognosis and presented for necropsy. Gross, histopathologic, immunophenotypic, and ultrastructural findings confirmed a diagnosis of FPLCH. Proliferative cells were E‐cadherin+/Iba‐1+/CD18+/CD1a+/CD5+/MHCII+/CD204−/CD4−; transmission electron microscopy identified the presence of Birbeck granules in the proliferating histiocytes, consistent with previous reports of FPLCH. [ABSTRACT FROM AUTHOR]

Lanthanum carbonate (LC) is a phosphate binder used in end-stage renal disease (ESRD) with few adverse effects due to poor systemic absorption. Gastrointestinal deposition is likely due to alterations in epithelial permeability from inflammation in ESRD. It is challenging to detect in cases with minimal deposition and may be missed on endoscopy and biopsy. A 36-year-old with ESRD who was evaluated for gastrectomy was found to have LC deposition histologically. Years later, the excised portion had similar findings. This case allows for evaluation of LC gastropathy in a resection specimen, providing the opportunity to showcase its unique pathology features.

Abstract Background Glomerular lipidosis is a rare histological feature presenting the extensive glomerular accumulation of lipids with or without histiocytic infiltration, which develops under various conditions. Among its various etiologies, macrophage activation syndrome (MAS) is a condition reported to be associated with histiocytic glomerular lipidosis. Here we describe the first case of glomerular lipidosis observed in a renal allograft that histologically mimicked histiocytic glomerulopathy owing to MAS. Case presentation A 42-year-old man underwent successful living-donor kidney transplantation. However, middle-grade proteinuria and increased serum triglyceride levels indicative of type V hyperlipidemia developed rapidly thereafter. An allograft biopsy performed 6 months after the transplantation showed extensive glomerular infiltration of CD68+ foam cells (histiocytes) intermingled with many CD3+ T-cells (predominantly CD8+ cells). Furthermore, frequent contact between glomerular T-cells and histiocytes, and the existence of activated CD8+ cells (CD8+, HLA-DR+ cells) were observed by double immunostaining. There was no clinicopathological data suggesting lipoprotein glomerulopathy or lecithin cholesterol acyltransferase deficiency, both of which are well-known causes of glomerular lipidosis. The histological findings were relatively similar to those of histiocytic glomerulopathy caused by MAS. As systemic manifestations of MAS, such as fever, pancytopenia, coagulation abnormalities, hyperferritinemia, increased liver enzyme levels, hepatosplenomegaly, and lymphadenopathy were minimal, this patient was clinicopathologically diagnosed as having renal-limited MAS. Although optimal treatment strategies for MAS in kidney transplant patients remains unclear, we strengthened lipid-lowering therapy using pemafibrate, without modifying the amount of immunosuppressants. Serum triglyceride levels were normalized with this treatment; however, the patient’s extensive proteinuria and renal dysfunction did not improve. Biopsy analysis at 1 year after the transplantation demonstrated the disappearance of glomerular foamy changes, but the number of glomerular infiltrating cells remained similar. Conclusion To our knowledge, this is the first reported case of glomerular lipidosis in a transplanted kidney. Increased interaction-activation of histiocytes (macrophages) and CD8+ T-cells, the key pathogenic feature of MAS, was observed in the glomeruli of this patient, who did not demonstrate overt systemic manifestations, suggesting a pathological condition of renal-limited MAS. The clinical effects of triglyceride-lowering therapy were limited, suggesting that hypertriglyceridemia was not the cause of but rather may be a consequence of renal-limited MAS.

Background: Glomerular lipidosis is a rare histological feature presenting the extensive glomerular accumulation of lipids with or without histiocytic infiltration, which develops under various conditions. Among its various etiologies, macrophage activation syndrome (MAS) is a condition reported to be associated with histiocytic glomerular lipidosis. Here we describe the first case of glomerular lipidosis observed in a renal allograft that histologically mimicked histiocytic glomerulopathy owing to MAS. Case presentation: A 42-year-old man underwent successful living-donor kidney transplantation. However, middle-grade proteinuria and increased serum triglyceride levels indicative of type V hyperlipidemia developed rapidly thereafter. An allograft biopsy performed 6 months after the transplantation showed extensive glomerular infiltration of CD68+ foam cells (histiocytes) intermingled with many CD3+ T-cells (predominantly CD8+ cells). Furthermore, frequent contact between glomerular T-cells and histiocytes, and the existence of activated CD8+ cells (CD8+, HLA-DR+ cells) were observed by double immunostaining. There was no clinicopathological data suggesting lipoprotein glomerulopathy or lecithin cholesterol acyltransferase deficiency, both of which are well-known causes of glomerular lipidosis. The histological findings were relatively similar to those of histiocytic glomerulopathy caused by MAS. As systemic manifestations of MAS, such as fever, pancytopenia, coagulation abnormalities, hyperferritinemia, increased liver enzyme levels, hepatosplenomegaly, and lymphadenopathy were minimal, this patient was clinicopathologically diagnosed as having renal-limited MAS. Although optimal treatment strategies for MAS in kidney transplant patients remains unclear, we strengthened lipid-lowering therapy using pemafibrate, without modifying the amount of immunosuppressants. Serum triglyceride levels were normalized with this treatment; however, the patient's extensive proteinuria and renal dysfunction did not improve. Biopsy analysis at 1 year after the transplantation demonstrated the disappearance of glomerular foamy changes, but the number of glomerular infiltrating cells remained similar. Conclusion: To our knowledge, this is the first reported case of glomerular lipidosis in a transplanted kidney. Increased interaction-activation of histiocytes (macrophages) and CD8+ T-cells, the key pathogenic feature of MAS, was observed in the glomeruli of this patient, who did not demonstrate overt systemic manifestations, suggesting a pathological condition of renal-limited MAS. The clinical effects of triglyceride-lowering therapy were limited, suggesting that hypertriglyceridemia was not the cause of but rather may be a consequence of renal-limited MAS. [ABSTRACT FROM AUTHOR]

A 14‐years‐old squirrel monkey was euthanized due to weakness. Histopathological examination revealed multifocal growth of oval cells with severe atypia in the liver, spleen, and bone marrow. The neoplastic cells were positive for histiocytic markers (Iba1, HLA‐DR, CD204). This is the fourth case of histiocytic sarcoma in non‐human primates. [ABSTRACT FROM AUTHOR]

Herein, we present a clinicopathological and molecular analysis of four cases of endometrial carcinoma (EC) diffusely exhibiting dyshesive cells with wide eosinophilic and vacuolated cytoplasm (histiocyte-like tumor cells, HLTCs). We compared these HLTCs to similar cells found in microcystic, elongated and fragmented (MELF) pattern (n = 20) or after neoadjuvant chemotherapy (NAC) (n = 5). The four cases were endometrioid, serous, clear cell, and gastric-type; all were at FIGO stage ≥ III. HLTCs showed an epithelial Müllerian phenotype and at least focal CK20, HNF1β, and CK5/6 expression, with aberrant e-cadherin and β-catenin expression; two cases were MMR-deficient, and one was p53-abnormal; all were POLE wild type. MELF-associated and NAC-associated HLTCs showed similar morphological/immunophenotypical features. However, MELF-associated HLTCs were mainly intraglandular and inflammation-associated, did not form a distinct tumor component, and showed no relationship with lymph node metastases. In conclusion, different histotypes of EC may show a prominent HLTC component, which shows peculiar morphological/immunophenotypical features and appears associated with aggressive behavior. [ABSTRACT FROM AUTHOR]

La maladie de Gaucher est la plus fréquente des maladies de surcharge lysosomale. La présentation clinique est hétérogène, allant de formes très symptomatiques diagnostiquées durant l'enfance à d'autres, pauci-symptomatiques tout au long de la vie. Dans ces derniers cas, l'hypothèse diagnostique d'une maladie de Gaucher est parfois difficile à évoquer. Elle peut pourtant avoir un retentissement sur la qualité de vie des patients, alors que des traitements efficaces existent. Le cas rapporté ici est celui d'un homme de 59 ans, hospitalisé pour hépatite aiguë grave, chez qui une maladie de Gaucher a été découverte de manière fortuite lors d'un myélogramme réalisé pour explorer de profondes cytopénies. Gaucher disease is one of the most common lysosomal storage disorders. The disease may take several clinical forms, ranging from severe symptoms and childhood diagnosis, to paucisymptomatic cases throughout life. In the latter, the diagnosis of Gaucher disease could be challenging. However, it can have an impact on patient's quality of life, even though effective treatments exist. Here is reported the case of a 59-year-old man, hospitalized for severe acute hepatitis, in whom a Gaucher disease was incidentally discovered on a bone marrow aspiration, performed to explore severe cytopenias. [ABSTRACT FROM AUTHOR]

Rosai–Dorfman disease (RDD) is a nonneoplastic histiocytic proliferation. RDD is CD1a negative as opposed to Langerhans cell histiocytosis (LCH). The lesion was positive for CD1a immunohistochemistry in our RDD patient, suggesting an overlap with LCH. In addition, our case exhibited granulomatous angiitis (GA) on microscopy. We report the first triad of coexistent intracranial RDD-LCH-GA. A 30-year-old man presented with seizures, limb weakness, and violent behavior for 3 months. There was no fever, lymphadenopathy, or hepatosplenomegaly. Laboratory test results were normal. Radioimaging revealed an 8.6 cm × 7.4 cm × 3.2 cm mass in the parietotemporal lobe. It was hypointense on T1W1 and hypointense on T2W1, suggestive of glioma or tumefactive demyelination. A subtotal resection was performed. Histopathology exhibited mature lymphocytes, plasma cells, and histiocytes with emperipolesis. Vessels showed transmural granulomatous inflammation. Fungal and mycobacterial stains were negative. Immunohistochemistry revealed positivity for CD68, S100, and CD1a. The patient refused to undergo postoperative adjuvant radiotherapy. He remained asymptomatic for 6 months but was lost to follow-up thereafter. RDD-LCH concurrence may represent a clonal transformation in a common precursor histiocyte. Coexistent GA requires resection followed by steroid or cyclophosphamide therapy to prevent disease progression.

Nodular histiocytic/mesothelial hyperplasia (NHMH) is a benign entity that can simulate malignancies histologically. NHMH was initially described in 13 hernia sacs in 1975. Since then, several cases and case series of NHMH have been reported in the literature with variable nomenclatures. It is always an incidental finding seen in a wide range of patient populations with no predilection for gender, age or race. It is most commonly found on mesothelium-lined surfaces such as peritoneum but can also be seen at other sites. It is hypothesized that NHMH occurs due to irritation of mesothelial surfaces and interaction of adhesion molecules. The histologic mimicry by NHMH of malignant processes can pose a diagnostic challenge. This review aims to highlight clinical and pathological aspects of NHMH and to cover common differential diagnoses with special attention to those pertaining to gastrointestinal tract pathology.

Abstract Background With the recent increased use of lanthanum carbonate, several cases of lanthanum phosphate deposition to gastric mucosa in dialysis patients have been reported. However, the endoscopic appearance of the early-stage lesion and the over-time alterations of endoscopic findings due to the progression of lanthanum phosphate deposition remain unclear. Case presentation An 80-year-old man receiving dialysis and taking lanthanum carbonate as a phosphate binder over a 4-year period underwent upper gastrointestinal endoscopy four times beginning 1 year after initiation of treatment. The first endoscopic examination (after 1 year of exposure to lanthanum carbonate) revealed rough mucosa with a few areas of white granular mucosa. Over the 3 years of endoscopic follow-up, the white granular mucosa spread and multiple erosions appeared. Histopathological findings of biopsy specimens from an erosion showed extensive infiltration by histiocytes containing deposits. Scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX) revealed that the presence of the deposits containing phosphorus and lanthanum in the gastric mucosa. On the basis of these results, the patient was diagnosed with gastropathy associated with lanthanum phosphate deposition. Conclusions Over a 3-year period, endoscopic findings associated with lanthanum deposition gradually changed and expanded from the early stage.

Feline histiocytic diseases are uncommon and rarely reported. Feline progressive histiocytosis (FPH) is the most common histiocytic disease in cats, predominantly affecting middle-aged animals. The most common presentation is the cutaneous form with solitary or multiple cutaneous nodules. A female, mixed-breed 6-year-old cat was presented with a 9-month history of a nodule in the nasal planum and was diagnosed by histopathology with histiocytic proliferation. At the time of diagnosis, new nodules were discovered on the lower lip, digit, and two lesions in the tail region, with the largest measuring 1.5 cm. Supplementary immunohistochemistry, showed immunolabeling for Iba-1 that in combination with the clinical course of the disease, confirmed the diagnosis of FPH. No response to chemotherapy treatment with lomustine alternated with doxorubicin was achieved. Toceranib phosphate resulted in a transient response and, stable disease for a short period (6 weeks). Electrochemotherapy with bleomycin was initiated and resulted in partial remission. Later on, chlorambucil was also started. Ultimately, the combination of all three treatments led to a complete response and disappearance of all the lesions. FPH is considered a disease resistant to various treatments, and effective treatments have not been reported. In this case report, we describe a successful multimodal therapeutic approach that resulted in complete resolution of the FPH and long-term survival (460 days without external lesions at the time of death). Further studies are necessary to confirm the efficacy of this therapeutic approach., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The author(s) declared that they were an editorial board member of Frontiers, at the time of submission. This had no impact on the peer review process and the final decision., (Copyright © 2024 Sena, Turquete, Pimentel, Almeida, Lavalle, Nakagaki, Giuliano, Paes and Horta.)

We report a histiocytic sarcoma originating from the epididymis observed in a 110-week-old male CD-1 mouse in a carcinogenicity study. At necropsy, no lesions were observed in the epididymis. Histologically, a neoplastic lesion was observed in the cauda of the epididymis that was well demarcated from the surrounding tissues. The lesion mainly consisted of spindle-shaped tumor cells with oval to elongated nuclei and abundant eosinophilic or foamy cytoplasm. The tumor cells were arranged in a fascicular pattern, interlacing bundles, or a whorl pattern. The nuclei showed mild atypia with irregular shapes and varied sizes, whereas few mitotic figures and no typical multinucleated cells were observed. The epididymal ducts remained within the neoplastic lesion, and the tumor cells invaded between the epithelium and the smooth muscle layer of the epididymal duct. Immunohistochemically, the tumor cells were positive for vimentin and macrophage markers (Iba1, CD204, F4/80, and Mac-2) but negative for cytokeratin and other mesenchymal cell (α-smooth muscle actin, desmin, CD31, and platelet-derived growth factor receptor-β), neural cell (S-100 and nestin), or Leydig cell markers (calretinin). Proliferating cell nuclear antigen-positive tumor cells were sporadically observed in the lesion. Based on these results, the tumor was diagnosed as a histiocytic sarcoma originating from the epididymis. This report provides additional histopathological evidence of spontaneous histiocytic sarcomas originating from the epididymis of aged mice., Competing Interests: The authors declare that they have no conflicts of interest to disclose in connection with this report., (©2024 The Japanese Society of Toxicologic Pathology.)

A recent study revealed that recurrence of myocarditis occurs in a significant proportion of patients, but multiple recurrences of myocarditis have rarely been reported. The pathophysiology and best treatments for multiple recurrences of myocarditis remain unclear. A 60-year-old man presented to our emergency department with fever and chest pain. Physical examination, imaging, and laboratory findings were consistent with fulminant myocarditis. Paired titers confirmed adenovirus infection. The patient was treated with intra-aortic balloon pump and percutaneous cardiopulmonary support for 7 days and was discharged with near-normal electrocardiographic and echocardiographic findings on day 26. Over the subsequent 3 years, the patient experienced six episodes of recurrence of myocarditis with a progressive decrease in his ability to perform activities of daily living. At the time of his sixth recurrence, he died of ventricular fibrillation. Autopsy revealed mild enlargement of the left ventricle, extensive inflammatory cell infiltration, and mild interstitial fibrosis, suggesting left ventricle remodeling because of repetitive myocarditis. We have presented a case of multiple recurrences of myocarditis. This is the largest number of recurrences in a single patient reported to date. Further studies are needed to elucidate the underlying pathogenesis and best treatment of this condition. < Learning objective: Although few cases of multiple recurrent myocarditis have been reported, we recently experienced a case of multiple recurrences of myocarditis over a 3-year period. However, we did not definitively diagnose the etiology of myocarditis or perform etiologically based medical therapy, so we could not rescue our patient. In cases of multiple recurrent myocarditis, more aggressive and accurate investigation are required to elucidate the etiology and pathophysiology of this condition.> [ABSTRACT FROM AUTHOR]

A 13-year-old castrated male Maine coon cat with a 5-year history of atypical mycobacteriosis was euthanized and submitted for necropsy. The cat had been kept in clinical remission since diagnosis using a combination of the antimycobacterial drug clofazimine and additional multimodal antimicrobial therapy. Grossly, tissues were diffusely discolored red-brown to yellow. Histologically, the myocardial interstitum was expanded by numerous, often multinucleated cells, which were distended by uniformly shaped acicular cytoplasmic spaces. These cells were immunopositive for CD18 and immunonegative for desmin, suggesting a histiocytic rather than muscular origin. Macrophages in other tissues contained similar acicular spaces. Ultrastructurally, the spaces were surrounded by 2 lipid membranes, resembling an autophagosome. Based on the clinical history and histologic, immunohistochemical, and ultrastructural data, we diagnosed clofazimine crystal storage. To our knowledge, this is the first report of clofazimine storage in a cat or within myocardial interstitial macrophages. [ABSTRACT FROM AUTHOR]

Langerhans Cell Histiocytosis (LCH) is a rare disorder of the reticuloendothelial system associated with proliferation of Langerhans cells and mature eosinophils. The hallmark of LCH is the proliferation and accumulation of a specific histiocyte: the Langerhan’s cell. Any organ or system can be affected. Here, a case of multisystem LCH with skeletal, lung and hepatobiliary involvement in a two-year child who presented with painless forehead swelling following trauma. The patient was systematically worked up with blood investigations, imaging and histopathological analysis which ultimately revealed the diagnosis of LCH. This case report is unique in that it presented with involvement of temporal bone wherein it can be confused with inflammatory pathologies like Cholesteatoma and tumours like Rhabdomyosarcoma. The child was started on vinblastine based chemotherapy and showed good response to therapy. This case report discusses the imaging differential diagnosis in temporal bone LCH along with utility of Positron Emission Tomography and Computed Tomography (PET-CT) in planning treatment of these cases.

Lanthanum carbonate (LC) is a phosphate binder used in end-stage renal disease (ESRD) with few adverse effects due to poor systemic absorption. Gastrointestinal deposition is likely due to alterations in epithelial permeability from inflammation in ESRD. It is challenging to detect in cases with minimal deposition and may be missed on endoscopy and biopsy. A 36-year-old with ESRD who was evaluated for gastrectomy was found to have LC deposition histologically. Years later, the excised portion had similar findings. This case allows for evaluation of LC gastropathy in a resection specimen, providing the opportunity to showcase its unique pathology features.

Background: Granulomas are the commonest lesions that the pathologists come across in routine practice. Granulomatous inflammation is a special type of chronic inflammation that is a manifestation of many infective, toxic, allergic, autoimmune and neoplastic diseases and also conditions of unknown etiology. The aim of this study is to analyze different granulomatous lesions and to find the frequency and etiology of all granulomatous lesions.Materials and Methods: The study included a total of 218 granulomatous lesions, received over a period of one year from July 2013 to June 2014 in the department of pathology, TUTH. Special stains like Ziehl-Neelsen, PAS and Wade- Fite- Faraco were done whenever required.Results: Granulomatous lesion accounted for 3% of all biopsies. The median age of the patients was 29 years and the majority of the patients were in the age group of 20-29 years with no sex predilection. Majority of granulomas were seen in lymph nodes (32.1%), followed by skin and subcutis (29.4%), and bones and joints (11%). Tuberculosis was the most common cause of granuloma with 143 (65.6%) cases, followed by leprosy, foreign body and fungal infection. The most common type of granuloma was epithelioid (87.2%), followed by epithelioid with suppuration, histiocytic, foreign body and mixed inflammatory.Conclusion: The granulomatous lesion is common in third decade of life with no sex predominance. The commonest site is lymph node with tuberculosis being the most common cause followed by leprosy. The epithelioid type was the most common type of granuloma.

The burden of community-acquired pneumonia (CAP) requiring hospitalization among adults is substantial and is a leading infectious cause of hospitalization and death. Severe CAP may rarely get complicated with secondary hemophagocytic lymphohistiocytosis (HLH). The term hemophagocytosis refers to the pathologic finding of activated macrophages engulfing erythrocytes, leukocytes, platelets, or their precursor cells in the bone marrow, liver, or lymph nodes; this being characteristic for hemophagocytic syndrome. HLH can be primary or secondary and has a high mortality if left untreated. We report a case of severe CAP with secondary HLH in a 26-year-old male, who presented with fever, pancytopenia, jaundice, and pneumonia due to polymicrobial infection. This case report is presented to enlighten clinicians about the clinical entity of HLH and to suspect and recognize this rare and fatal disease.

Histiocytic proliferative diseases are rare in cats, and their pathogenesis is poorly understood. In the present study, 25 cases of histiocytic sarcoma (HS) and 6 of feline progressive histiocytosis (FPH) were examined, and survival times were recorded in 19 cases. The immunophenotypes of tumor cells in these cases as well as of nonneoplastic feline histiocytes were characterized using formalin-fixed, paraffin-embedded tissues. An FPH cell line (AS-FPH01) and xenotransplant mouse model of FPH were also established. The median survival time of HS (150 days) was significantly shorter than that of FPH (470 days). Immunohistochemically, nonneoplastic histiocytes were immunopositive for various combinations of Iba-1, HLA-DR, E-cadherin, CD204, CD163, CD208, and MAC387. By immunohistochemistry, dermal interstitial dendritic cells (iDCs) and macrophages were CD204+/E-cadherin−, while epidermal Langerhans cells (LCs) were CD204−/E-cadherin+. Neoplastic cells of 4 FPH and 18 HS were CD204+/E-cadherin− (iDC/macrophage immunophenotype), while 2 FPH and 2 HS were CD204−/E-cadherin+ (LC immunophenotype), and 5 HS were CD204+/E-cadherin+ (LC-like cell immunophenotype). Furthermore, immunohistochemical and western blot analyses of AS-FPH01 cells derived from E-cadherin-negative FPH revealed that cultured cells were immunopositive for both CD204 and E-cadherin in vitro and in vivo. These results indicate that the neoplastic cells of feline HS and FPH were variably positive for iDC/macrophage and LC markers, and their immunophenotype changed in different microenvironments. The novel cell line established in the present study may serve as an experimental model of FPH that will enable further molecular and therapeutic studies on this disease. [ABSTRACT FROM AUTHOR]

Juvenile xanthogranuloma (JXG) and cutaneous mastocytosis (CM) are two distinct conditions that have rarely been reported in association. We report a child with CM and disseminated JXG, who showed a significant decrease in serum tryptase levels and regression of JXG lesions over time. Due to the paucity of reports, a true association between these two conditions has not been validated, although a potential induction of histiocytic lesions by mast cell degranulation has been proposed. [ABSTRACT FROM AUTHOR]

Reticulum cell hyperplasia (RCH) was a term used for many years by the National Toxicology Program (NTP) to describe a certain non-neoplastic bone marrow lesion of rats. Retrospective microscopic evaluation of RCH lesions and immunohistochemistry analyses were performed to reassess and further characterize these lesions. The NTP database was searched to identify femoral bone marrow specimens diagnosed with RCH from 1981 to 2014 (n = 254). The diagnosis last occurred in 2003, after which the term "cellular infiltration" was used. Eighty-three RCH slides, spanning 22 years, representing 34 different chemicals, were selected for microscopic review, and a subset (23) was chosen for ionized calcium binding adapter molecule 1 (Iba1) immunohistochemical staining; initial investigations revealed Iba1 worked as a macrophage marker on decalcified tissue. The following diagnoses were made upon reevaluation: 36 were consistent with cellularity increased, macrophage, 22 with histiocytic sarcoma, 8 with increased myeloid cells, 4 with autolysis, and 13 were normal appearance. All 23 RCH lesions stained positive for Iba1. Fifty-eight of 83 bone marrows previously diagnosed with RCH are consistent morphologically and immunohistochemically with cells of histiocytic origin. These results will help with interpretation of historical data and demonstrates that Iba1 can be used in decalcified bone marrow sections. [ABSTRACT FROM AUTHOR]