Sarcoidosis and granuloma annulare (GA) are two granulomatous skin conditions with significant clinical and histopathologic overlap, whose diagnosis may be further complicated by their potential to co-exist within a similar patient. Evolving literature supports the utility of special staining and immunohistochemistry (IHC) to aid in distinguishing these and other granulomatous skin disorders. Herein we report an interesting case of GA-like lesions in a patient with sarcoidosis, the elucidation of which was aided by immunohistochemical analysis. A 50-year-old man with an established history of sarcoidosis presented to the clinic with erythematous papules and plaques on his left elbow. Skin biopsy showed a granulomatous infiltrate consisting of histiocytes palisading around necrobiotic collagen with an accompanying perivascular lymphohistiocytic infiltrate. Staining with colloidal iron (increased mucin), CD123 (clusters of plasmacytoid dendritic cells), and adipophilin (highlighting histiocytes and necrobiosis), along with the histologic features supported a diagnosis of GA. The distinction between these two entities is important, as sarcoidosis may manifest systemically. Our case adds to the limited existing literature on GA-like lesions in sarcoidosis, underscoring the utility of special stains and IHC to help render the most accurate diagnosis for the patient.

Graft-versus-host disease-associated angiomatosis (GVHD-AA) is a rare clinicopathologic variant of chronic GVHD characterized by benign vascular proliferations arising within areas of sclerodermatous skin change. The entity was formally named in 2014 and presents clinically as red-to-violaceous papules or nodules, confined to fibrotic GVHD skin. We present a case of GVHD-AA in a 29-year-old man with Philadelphia chromosome-positive acute lymphoblastic leukemia, diagnosed in 2017 and treated with matched unrelated donor allogeneic peripheral blood stem cell transplantation. His posttransplant course has been notable for severe chronic GVHD of the skin, eyes, mouth, and lungs, refractory to multiple systemic agents. His dermatologic symptoms began as sclerosis of the skin in the hands, arms, shoulders, and upper thighs, and have since progressed to involve 80% of his body surface area in 2025. Since 2023, he began developing numerous scaly red nodules overlying the scleroderma, which have been managed by shave removal, cauterization, and β-blocker therapy. Histological examination of shave biopsies from the arms and back shows an angiomatous proliferation with angiokeratoma-like features and Masson-like change. Endothelial cells are cytologically bland, and HHV8 immunohistochemistry is negative. This case adds to the limited body of histologically documented GVHD-AA and underscores the importance of recognizing this entity in sclerodermatous GVHD skin and relaying its prognosis and management to multidisciplinary clinical teams.

Cutaneous iododerma is a rare adverse reaction to iodine-containing compounds that may clinically and histopathologically mimic infection, vasculitis, malignancy, and other neutrophilic dermatoses. Although most commonly associated with iodinated contrast exposure, a variety of predisposing factors and potential associations have been reported, including impaired renal function, repeated iodine exposure, and more recently, hydralazine therapy in isolated cases. We report two women with chronic kidney disease and recent iodinated contrast exposure who developed rapidly progressive, painful, bullous, erosive, and retiform eruptions after contrast administration. Both patients had concurrent hydralazine exposure. Initial clinical considerations included deep fungal infection, ecthyma, Sweet syndrome, drug eruption, and vasculitis. Histopathologic examination demonstrated a neutrophil-rich dermal infiltrate with numerous basophilic haloed cryptococcoid bodies and vasculitis with fibrinoid necrosis. Fungal, bacterial, and acid-fast stains were negative, and extensive infectious evaluations were unrevealing. Markedly elevated serum and urine iodine levels supported the diagnosis of iododerma. Both patients exhibited multiple immunologic abnormalities, including positivity or elevated levels of p-ANCA and antinuclear, anti-histone, anti-myeloperoxidase, and anti-proteinase 3 antibodies. These findings were interpreted cautiously given concurrent hydralazine exposure, the absence of definitive systemic autoimmune vasculitis, and the potential for reactive serologic abnormalities in the setting of intense neutrophilic inflammation. Both patients improved following corticosteroid therapy, iodine clearance, and discontinuation of hydralazine. These cases emphasize the diagnostic importance of recognizing haloed cryptococcoid bodies within a neutrophil-rich infiltrate associated with vasculitic injury as part of the histopathologic spectrum of iododerma. The significance of hydralazine exposure in the pathogenesis of iododerma remains uncertain and warrants further investigation.

Onychomatricoma (OM) is a rare benign fibroepithelial nail unit tumor that remains frequently underrecognized, with evolving histopathologic criteria. Existing descriptions have largely focused on well-developed lesions, leaving the histopathologic features of smaller, localized lesions poorly characterized. We report an attenuated OM in a 45-year-old woman highlighting subtle but characteristic histopathologic features of OM, including a focal CD34-positive spindle cell population in the superficial submatrical dermis, matrical epithelial papillation, and focal serum-filled cavity formation within the nail plate. Compared with classic OM, these findings were more localized and less architecturally developed, while still retaining key diagnostic features. Improved recognition of these subtle features in attenuated lesions will facilitate earlier diagnosis, reduce misclassification, and refine clinicopathologic criteria for this important nail unit tumor.

Several activating mutations and gene fusions involving the mitogen-activated protein kinase (MAPK) pathway have appeared in the literature regarding histiocytic neoplasms. We identified a GAB2::BRAF fusion in a cutaneous lesion of a 36-year-old male who developed central diabetes insipidus and reddish-pink grouped papules on the bilateral axillary rims, inguinal region, and periocular skin. Skin biopsy obtained from an axillary lesion showed a CD68+, S100-, and CD1a- histiocytic proliferation with foamy histiocytes and multinucleated Touton giant cells, compatible with xanthogranuloma. Next-generation sequencing identified a GAB2::BRAF fusion involving Exon 2 of GAB2 and Exon 10 of BRAF. Our case further highlights this novel fusion in the MAPK signaling pathway as a possible driver of nonLangerhans cell histiocytosis (NLCH) and underscores the utility of performing molecular studies on skin biopsy specimens with NLCH to help identify potential targets for therapy.

Porokeratotic Adnexal Ostial Nevus (PAON) is an uncommon disorder characterized by abnormal keratinization affecting eccrine and follicular adnexa. Initially described separately as porokeratotic eccrine ostial and dermal duct nevus and porokeratotic eccrine and hair follicle nevus, the term PAON was introduced in 2009 to encompass these conditions. PAON presents with diverse clinical manifestations, ranging from asymptomatic keratotic papules and plaques to verrucous lesions. Typically appearing at birth, PAON can rarely manifest in adulthood. We report a case of a porokeratosis-spectrum lesion with features overlapping with PAON in a male patient in his 30s presenting with longitudinal splitting of the left thumbnail associated with an erythematous linear lesion extending from the nail matrix, alongside a scaly plaque on the proximal nail fold and dorsal thumb. This case highlights the importance of considering porokeratosis-spectrum disorders, including lesions with PAON-like features, in the differential diagnosis of monodactylous erythronychia and onychodystrophy, particularly due to its potential for subtle cutaneous involvement as was present in this case. This instance represents a rare presentation of a porokeratosis-spectrum lesion involving the nail unit epithelium and contributes to the expanding clinical spectrum of porokeratosis with PAON-like features.

Loncastuximab tesirine (LT) is an antibody-drug conjugate (ADC), a novel class of therapeutics that combines a target-specific monoclonal antibody with a cytotoxic agent via a chemical linker. LT has been approved in the United States as therapy for relapsed or refractory diffuse large B-cell lymphoma (DLBCL). Given the novelty of this drug, cutaneous adverse effects remain poorly characterized. In this case report, we present a 35-year-old male with relapsing and refractory DLBCL who developed a bullous eruption after his third cycle of LT. Physical exam revealed scattered erosions and erythema of the neck and extremities, along with multiple bullae and erosions on the hands and dorsal feet, and vesicles on the shin. Histopathological exam revealed basovacuolar alteration with epidermal dysmaturation and a re-epithelializing blister, features suggestive of toxic erythema of chemotherapy (TEC). Direct immunofluorescence was negative for immune complex deposition. To date, there are only three cases of LT-associated bullous eruptions in the literature, all demonstrating subepidermal blistering with granular IgA deposition along the basement membrane. This case lacks immunoglobulin deposition and instead exhibits TEC-like cytotoxic interface dermatitis. This case expands the clinicopathologic spectrum of LT-associated cutaneous toxicity and highlights a distinct non-immune mediated, TEC-like vesiculobullous presentation.

IgG4-related disease (IgG4-RD) is a systemic fibroinflammatory disorder characterized by dense infiltration of IgG4-positive plasma cells, fibrosis, and elevated serum IgG4 levels. Although various cutaneous manifestations of IgG4-RD have been described, and vasculitic changes have occasionally been reported, granulomatous vasculitis is not considered a typical histopathological feature of cutaneous IgG4-RD. We report a 93-year-old woman with a history of IgG4-RD who presented with long-standing subcutaneous nodules on both knees. Histopathological examination revealed dense lymphoplasmacytic infiltration with marked fibrosis, obliterative phlebitis, and granulomatous vasculitis characterized by vascular destruction with multinucleated giant cells. Immunohistochemistry demonstrated a marked increase in IgG4-positive plasma cells with a high IgG4/IgG-positive plasma cell ratio. Comprehensive clinical, serological, and histopathological evaluation excluded other causes of granulomatous vasculitis, including eosinophilic granulomatosis with polyangiitis, granulomatosis with polyangiitis, and sarcoid vasculitis. The lesions responded favorably to systemic corticosteroid therapy. To our knowledge, granulomatous vasculitis has not been recognized as a typical histopathological feature of cutaneous IgG4-RD. This case suggests that granulomatous vasculitis may rarely occur in cutaneous lesions of IgG4-RD, but additional cases are needed to confirm this association.

CD30-positive large-cell proliferations arising in patients with mycosis fungoides can be diagnostically challenging, particularly when they show variable T-cell receptor expression or gamma/delta (γδ) phenotype. We present two cases of mycosis fungoides (MF) with CD30-positive large cell transformation (LCT)/progression exhibiting γδ T-cell phenotypic evolution. Case 1, a 50-year-old woman, initially presented with hyperpigmented patches and papulonodular lesions showing epidermotropic small-cell MF alongside dermal CD30-positive large cells with a γδ phenotype. Over ten years, she developed recurrent cutaneous and eventually nodal disease with phenotypic shifts between γδ and αβ expression, while molecular studies confirmed a single clonal process across all biopsies. Potentially pathogenic variants in FAS and CD70 were identified. Case 2, a 72-year-old man with longstanding MF, developed CD30-positive LCT initially with an αβ phenotype that subsequently acquired γδ expression and DUSP22 rearrangement. Oncoscan microarray revealed shared copy-number alterations including CDKN2A/B loss across temporally distinct biopsies, and sequencing identified KMT2C and TET1 variants. Both cases illustrate that MF can exhibit dynamic T-cell receptor phenotypic evolution, posing significant diagnostic challenges with lymphomatoid papulosis and primary cutaneous γδ T-cell lymphoma. Clonal identity confirmation through molecular studies is essential for accurate classification.