Necrobiotic Xanthogranuloma (NXG) is a rare non-Langerhans histiocytosis often associated with paraproteinemia or hematologic disease. NXG is usually characterized by yellow-orange, reddish-brown, or violaceous papules and nodules which may progress to form infiltrative plaques, with lesions often occurring in a periorbital distribution. Histopathologic study typically demonstrates bands of inflammatory granulomatous tissue separated by zones of necrobiosis, with the dermis and subcutaneous tissue most commonly affected. Historically, the diagnosis has been made based on consistent clinical and histologic findings, although diagnostic criteria have recently been proposed. Research on NXG is limited due to the condition's rarity, making comparisons between therapeutic agents difficult. Numerous systemic and localized treatments have been documented with varying responses. Necrobiotic Xanthogranuloma (NXG) is a rare form of non-Langerhans histiocytosis first described by Steven Kossard and Richard Winkelmann (1924 -2012) in August 1980.[1] NXG is characterized by yellow-orange, reddish-brown, or violaceous papules and nodules, which progress to form infiltrative plaques.[2] While most commonly found on the periorbital skin, lesions may occur across multiple sites, including the trunk, extremities, and extracutaneous tissues.[2] The histopathology is characterized by zones of necrobiosis separating bands of granulomatous infiltrate extending from the dermis to the subcutaneous tissue, with the epidermis often unaffected.[1] Touton-type giant cells, foreign-body giant cells, and foam cells are also frequently appreciated, and cholesterol clefts may be present.[3] Systemic paraproteinemia is associated with over 80% of patients with NXG and may precede or follow the initial presentation of cutaneous lesions for several years.[4-8] Evaluation for potential underlying disease and effective treatment is necessary. As NXG is a rare condition, research is limited to case reports and retrospective studies, limiting assessment for efficacy of therapeutic agents. Numerous systemic and localized therapies have been used with varying response.[2,9,10] We review the epidemiology, pathogenesis, clinical presentation, histopathology, diagnosis, and treatment of necrobiotic xanthogranuloma.

Chronic prurigo, formerly termed prurigo nodularis, is a chronic skin condition characterized by intensely itchy nodules and papules. It primarily affects adults, particularly middle-aged women. The aetiology of chronic prurigo is unclear, but it can be associated with primary skin dermatoses and systemic conditions. Minimal data on chronic prurigo in children are available in the literature. While systemic therapies for chronic prurigo have significant side effects, targeted biologic and small--molecule inhibitors offer a promising treatment option with a good benefit-risk ratio. We report one of the first cases of an adolescent with chronic prurigo that was successfully controlled with dupilumab. Dupilumab treatment resulted in a fast, significant and sustainable improvement in the signs and symptoms of chronic prurigo, with favourable safety and tolerability profiles, highlighting its potential for recalcitrant cases and long-term remission.

Cutaneous mast cell tumors have been described in all species of domestic mammals. However, information about these tumors in free-ranging and captive wild mammals is limited, with no reports in procyonids. This report aims to describe a case of disseminated cutaneous mast cell tumor in a captive South American coati (Nasua nasua). The animal was submitted to euthanasia and necropsy. On external examination, multiple papules, nodules, and plaques were distributed over the body surface. On cut section, they were soft and white. Histologically, they were composed of dense sheets of neoplastic cells interspersed with a delicate collagenous stroma. Cells were round and had a finely granular cytoplasm. Mast cell tumors were diagnosed based on histological features, positive staining with toluidine blue, and immunohistochemical labelling for the KIT protein. To the best of our knowledge, this is the first report of disseminated cutaneous mast cell tumor in this animal species.

Erythema elevatum diutinum (EED) is a rare and chronic form of cutaneous vasculitis often associated with systemic diseases including such hematologic malignancies as IgA monoclonal gammopathy, multiple myeloma, and non-Hodgkin lymphoma, as well as such autoimmune disorders and infections human immunodeficiency virus (HIV) and streptococcus. Clinically, EED presents as symmetrical red-to-brown papules, plaques, or nodules, primarily on extensor surfaces including the elbows, knees, and hands. These lesions may be asymptomatic or associated with burning, tenderness, or pruritus, and their chronic nature often leads to fibrosis and discoloration over time. Histologically, EED exhibits leukocytoclastic vasculitis associated with neutrophilic infiltration in the upper and mid dermis with sparing of the papillary and periadnexal dermis, fibrin deposition, and progressive dermal changes, including granulation tissue and fibrosis in late-stage lesions. While no cure exists, the first-line treatment is dapsone. Corticosteroids and immunosuppressive agents are employed for resistant cases. Early diagnosis and management are essential, particularly given the condition's potential to signal serious underlying systemic diseases. Although EED lesions may persist for decades, treating theunderlying conditions can influence the disease course, offering a pathway to improved outcomes.

Neutrophilic dermatoses are a group of rare heterogenous inflammatory disorders that share the presence of a sterile neutrophilic infiltrate on histopathology due to an underlying systemic illness, which can be a malignancy. This group of disorders can have diverse clinical presentations, including papules, plaques, nodules, vesiculopustular lesions, or ulcerations. We review the clinical and histopathologic features of several neutrophilic dermatoses that can be cutaneous manifestations of an underlying malignancy, including Sweet syndrome (acute febrile neutrophilic dermatosis), pyoderma gangrenosum, neutrophilic eccrine hidradenitis, subcorneal pustular dermatosis, erythema elevatum diutinum, Behçet's disease, Bazex syndrome, and VEXAS syndrome, We also discuss current treatment options. Cutaneous vasculitis, Schnitzler syndrome, and eosinophilic paraneoplastic dermatoses are also discussed in the context of cutaneous presentations of malignancy. These dermatologic conditions that may precede underlying malignancy.

Reactive granulomatous dermatitis (RGD) represents a broad group of cutaneous inflammatory skin conditions including interstitial granulomatous dermatitis (IGD), palisaded neutrophilic and granulomatous dermatitis (PNGD), and interstitial granulomatous drug reaction (IGDR). These conditions are frequently associated with autoimmune disorders and secondary to medications. They can also present as paraneoplastic syndromes. RGD usually presents as erythematous papules, plaques, or nodules, distributed symmetrically, especially on the inner aspect of the arms and thighs, the flank of the trunk, the lower part of the abdomen, and intertriginous areas like the axilla. Histologically, IGD classically reveals interstitial histiocyte and lymphocyte infiltration, plus multinucleated giant cells. As a paraneoplastic disease, IGD may occur in myelodysplastic syndromes, leukemias, and such solid tumors found in the breast and lungs. The successful diagnosis of IGD relies on both histopathologic examination and clinical evaluation. Although administration of corticosteroids can offer symptomatic relief of the skin lesions, treatment requires addressing the underlying condition when identified. Awareness of RGD's potential as an early marker for systemic disease, especially malignancy, is important for diagnostic and interventional purposes.

Hypertrophic lichen planus (HLP) is a chronic, T-cell-mediated inflammatory dermatosis characterized by verrucous, hyperkeratotic papules and predominantly affecting the lower extremities. Dermoscopy has emerged as a valuable non-invasive tool for diagnosing HLP; however, sequential dermoscopic documentation spanning multiple evolutionary stages within a single patient has rarely been reported. Here, we describe a 62-year-old male who presented with progressively enlarging hyperkeratotic nodules on the right lower leg, notably concentrated on the side affected by varicose veins. Dermoscopic examination of lesions at different anatomical sites simultaneously revealed distinct sequential features corresponding to discrete stages of HLP evolution: (1) structureless pigmented areas with hairpin and dotted vessels; (2) diffuse pigmentation with emerging Wickham striae and keratinous plugs (corn pearls); (3) volcano crater-like morphology with elevated keratinous plugs and violaceous striae; and (4) fully developed "bouquet of white roses" pattern with lobulated hyperkeratotic masses. Skin biopsy confirmed the diagnosis with irregular epidermal hyperplasia, wedge-shaped hypergranulosis, and a dense band-like lymphocytic infiltrate. This case demonstrates the full dermoscopic spectrum of HLP across lesions at different stages in a single patient at one time point, and highlights the probable role of chronic venous insufficiency in promoting Koebner-like lesion development. Our findings may assist clinicians in the non-invasive diagnosis and staging of HLP.

Lymphomatoid papulosis (LyP) is a primary cutaneous CD30+ lymphoproliferative disorder characterized by a chronic and self-healing recurrent cluster of erythematous papules or nodules on the skin of the trunk and/or extremities. The disease has an indolent clinical course with spontaneous regression or waxing and waning clinical evolution. The histopathologic spectrum of LyP is vast and may show few to numerous atypical cells immersed in a mild to intense inflammatory background. The backbone for the diagnosis is the positivity for CD30, which is one of the criteria to define this group of lymphoproliferative disorders. The association of these different histological and immunophenotypical findings is used to subclassify this disease in different subtypes from A to E, associated with DUSP22/IRF4 rearrangement, and other rare forms. Although this differentiation is important to raise awareness of different differential diagnosis, it does not impact the prognosis or change the treatment, which is usually centered in symptom relief and faster regression. In this review, we aim to summarize the most updated information of the clinical, histopathological, and molecular characteristics of LyP and provide a practical assessment for the diagnostic features that could help with the main differential diagnosis.

Primary cutaneous diffuse large B-cell lymphoma (PC-DLBCL) is a rare subtype of non-Hodgkin lymphoma with nonspecific cutaneous manifestations, leading to frequent misdiagnosis. This case describes an elderly patient with severe ulcerative skin lesions who was misdiagnosed repeatedly and required multidisciplinary orthopedic-hematologic management, thus providing valuable evidence for clinical practice. An 85-year-old male presented with progressive erythematous papules, ulcers, and subcutaneous nodules on the right forearm, chest, back, and left upper arm. Pathology and immunohistochemistry confirmed primary cutaneous diffuse large B-cell lymphoma. He underwent orthopedic debridement, autologous skin grafting, and 4 cycles of R-miniCHOP immunochemotherapy. Skin lesions resolved completely without recurrence, and 7-month follow-up showed favorable recovery. The key take-away is that PC-DLBCL is often misdiagnosed; early pathological biopsy and multidisciplinary collaboration between orthopedics and hematology-oncology are essential for accurate diagnosis and effective treatment to improve prognosis in elderly patients.