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Introduction Delayed-type drug hypersensitivity reactions (dtDHRs) are a major cause of morbidity and mortality, with considerable cost to healthcare systems (1-5). Skin is the most commonly affected organ. Severity ranges [...], Delayed-type drug hypersensitivity reactions are major causes of morbidity and mortality. The origin, phenotype, and function of pathogenic T cells across the spectrum of severity require investigation. We leveraged recent technical advancements to study skin-resident memory T cells (TRMs) versus recruited T cell subsets in the pathogenesis of severe systemic forms of disease, Stevens-Johnson syndrome/toxic epidermal necrolysis (SJS/TEN) and drug reaction with eosinophilia and systemic symptoms (DRESS), and skin-limited disease, morbilliform drug eruption (MDE). Microscopy, bulk transcriptional profiling, and single-cell RNA-sequencing (scRNA-Seq) plus cellular indexing of transcriptomes and epitopes by sequencing (CITE-Seq) plus T cell receptor sequencing (TCR-Seq) supported clonal expansion and recruitment of cytotoxic [CD8.sup.+] T cells from circulation into skin along with expanded and nonexpanded cytotoxic [CD8.sup.+] skin TRM in SJS/TEN. Comparatively, MDE displayed a cytotoxic T cell profile in skin without appreciable expansion and recruitment of cytotoxic [CD8.sup.+] T cells from circulation, implicating TRMs as potential protagonists in skin-limited disease. Mechanistic interrogation in patients unable to recruit T cells from circulation into skin and in a parallel mouse model supported that skin TRMs were sufficient to mediate MDE. Concomitantly, SJS/TEN displayed a reduced Treg signature compared with MDE. DRESS demonstrated recruitment of cytotoxic [CD8.sup.+] T cells into skin as in SJS/TEN, yet a pro-Treg signature as in MDE. These findings have important implications for fundamental skin immunology and clinical care.

Soft tissue vascular anomalies may be composed of arterial, venous, and/or lymphatic elements, and diagnosed prenatally or later in childhood or adulthood. They are divided into categories of vascular malformations and vascular tumors. Vascular malformations are further divided into low-flow and fast-flow lesions. A low-flow lesion is most common, with a prevalence of 70%. Vascular tumors may behave in a benign, locally aggressive, borderline, or malignant manner. Infantile hemangioma is a vascular tumor that presents in the neonatal period and then regresses. The presence or multiple skin lesions in an infant can signal underlying visceral vascular anomalies, and complex anomalies may be associated with overgrowth syndromes. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision process support the systematic analysis of the medical literature from peer reviewed journals. Established methodology principles such as Grading of Recommendations Assessment, Development, and Evaluation or GRADE are adapted to evaluate the evidence. The RAND/UCLA Appropriateness Method User Manual provides the methodology to determine the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where peer reviewed literature is lacking or equivocal, experts may be the primary evidentiary source available to formulate a recommendation. [ABSTRACT FROM AUTHOR]

Introduction: Blue rubber bleb nevus syndrome (BRBNS) is an uncommon vascular anomaly characterized by multifocal cutaneous, visceral, and other soft tissue or solid organ venous malformations. We observed that BRBNS lesions express immunohistochemical markers of lymphatic differentiation. Methods: BRBNS histopathologic specimens assessed at our institution during the past 27 years were reviewed. Slides from 19 BRBNS lesions were selected from 14 patients (9 cutaneous, 9 gastrointestinal, and 1 hepatic). We recorded the involved anatomical compartments and presence/absence of thrombi or vascular smooth muscle. Immunohistochemical endothelial expression of PROX1 (nuclear) and D2-40 (membranous/cytoplasmic) was evaluated semi-quantitatively. Results: Endothelial PROX1 immunopositivity was noted in all specimens; the majority (89.5%) demonstrated staining in more than 10% of cells. D2-40 immunopositivity was present in one-third (33%) of cutaneous lesions and only 1 gastrointestinal lesion. Conclusion: Endothelial cells in BRBNS almost always express 1 or more immunohistochemical markers of lymphatic differentiation. [ABSTRACT FROM AUTHOR]

PHACE (posterior fossa malformations, hemangiomas, arterial anomalies, cardiac anomalies, eye anomalies) association has many recognized clinical features. A link between PHACE and non‐vascular intracranial lesions has not been well‐described. We report three pediatric patients with PHACE and non‐vascular intracranial lesions. [ABSTRACT FROM AUTHOR]

Encephalocraniocutaneous lipomatosis (ECCL) is a rare neurocutaneous disorder caused by somatic FGFR1 and KRAS variants. It shares significant phenotypic overlap with several closely related disorders caused by mutations in the RAS‐MAPK pathway (mosaic RASopathies). We report a diagnostically challenging case of ECCL in which next‐generation sequencing of affected tissue identified a pathologic FGFR1 p.K656E variant, thereby establishing a molecular diagnosis. Patients with FGFR1‐associated ECCL carry a risk of developing malignant brain tumors; thus, genetic testing of patients with suspected ECCL has important management implications. [ABSTRACT FROM AUTHOR]

Introduction: Paraneoplastic pemphigus (PNP) is a rare, often fatal, autoimmune blistering disease of the skin and mucous membranes. In children, PNP is frequently associated with Castleman disease (CD). This series describes five cases of PNP associated with CD. Methods: Data were collected retrospectively from the medical records of patients with a diagnosis of PNP and CD from January 2013 to June 2022. Patients ≤22 years old with clinical and immunopathologic evidence of PNP were included; CD was diagnosed histopathologically. Results: Two children, two adolescents, and one young adult (two males, three females) were included. The average age at disease presentation was 11.8 years (range: 7–22 years). Oral (n = 5) and anogenital (n = 3) mucositis were common. Four patients had "unicentric" CD (UCD); one patient had "multicentric" CD (MCD). Castleman tumors were in the retroperitoneum (n = 4) or axilla (n = 1). One patient had myasthenia gravis without thymoma. Three patients had bronchiolitis obliterans (BO). Three patients had complete resection of their CD; two had partial resection. Three patients remain alive with a median follow‐up of 13 months (range: 12 months to 13 years); two are clinically stable with resolution of mucocutaneous lesions; one has persistent BO requiring ongoing ventilatory support. Patients who remain alive had UCD with complete resection; all deceased patients had partial resection and BO. Conclusion: Most patients had UCD, and the retroperitoneum was the most common location. Patients with MCD, incomplete resection, and BO died; patients with UCD and complete resection remain alive, even in the setting of BO. Consideration of PNP is critical when pediatric patients present with mucositis as PNP may be clinically indistinguishable from more common causes of mucositis. [ABSTRACT FROM AUTHOR]