Mechanical stress on the pilosebaceous unit can contribute to mechanical alopecia (MA) as seen with traction alopecia (TA) and trichotillomania (TTM). While some histological features that point to TA and TTM have been described, these may be absent in biopsies obtained at earlier stages of disease. Additional anomalies of the pilosebaceous unit have been observed that may assist in the histopathological detection of MA. A blinded, retrospective, qualitative, and semiquantitative study was performed comparing horizontally processed scalp biopsy sections of clinicopathologically confirmed TA (n = 16) and TTM (n = 9) to nearly matched controls (n = 15). Translocation of sebocytes into the follicular canal was seen in both TA and TTM, supporting a shared underlying mechanism. Vectorially warped sebaceous lobules were observed predominately in TA (p = 0.0002), while collapse of the inner root sheath of the lower follicular isthmus and surface lichenification were primarily seen in TTM (p < 0.0002). Lateral impingement of the follicular canal was seen in both TA and TTM (p < 0.0001), although more commonly in TA. These alterations were observed in the absence of other previously described features. Further validation studies in larger cohorts are warranted to assess their diagnostic utility in the recognition of MA.

We describe the novel occurrence of IgA pemphigus in a patient with long-standing systemic lupus erythematosus (SLE). SLE can be associated with the development of other autoimmune conditions, including cutaneous immunobullous disorders. To our knowledge, the co-occurrence of IgA pemphigus and SLE has not been previously reported in the literature. Potential common pathophysiological mechanisms are discussed.

Dupilumab inhibits the signaling pathway of interleukins 4 and 13, and can be effective in the management of treatment-refractory atopic dermatitis, with alopecia areata being uncommonly reported as a side effect and only limited to several cases. This is the case of a patient who experienced dupilumab-induced alopecia in treatment for atopic dermatitis and whose histological exam represented findings distinct from classical alopecia areata, telogen effluvium, or underlying psoriatic alopecia, with a potential explanation being inhibition of the Th2 pathway, enhancing a Th1-mediating response by the immune system leading to marked atrophy of the sebaceous glands, which is not reported in alopecia areata. While there is literature describing the potential growth effect of dupilumab in patients with alopecia, there are select reports, along with our case, that suggest its negative effects on the pilosebaceous unit and overall hair growth.

Lichen sclerosus (LS) is a chronic inflammatory skin disease typically affecting anogenital regions, with occasional extragenital involvement; however, its occurrence in acrochordons is seldom reported. We present eight cases of LS-like changes within acrochordons in patients with no prior history of LS elsewhere. Histopathologic examination confirmed characteristic LS features localized to the acrochordons. These findings raise questions about whether such changes represent a localized response to friction and/or chronic intermittent pressure-type trauma or a form of primary extragenital LS. Current literature suggests trauma as a key pathogenic mechanism in both classic LS and its manifestation within acrochordons, and our cases further support this hypothesis. Notably, neither our patients nor previously reported cases had documented LS at other sites, suggesting that LS-like changes in acrochordons may represent an incidental histopathologic finding that should not necessarily raise concern for the development of LS elsewhere.

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.