DiCaudo, David J.

Abstract Lichen Planopilaris (LPP) is a lymphocyte-mediated scarring alopecia characterized by progressive follicular destruction and fibrosis. In this clinical trial, patients with biopsy proven LPP were treated with deucravacitinib (an oral inhibitor of tyrosine kinase 2 (TYK2)) 6 mg BID for 24 weeks (NCT-06091956). Bulk and single-cell RNA sequencing was performed on paired pre- and post-treatment scalp biopsies from baseline and week 4. Patients (N=10) demonstrated improvements in PGA (88.9%, p=0.008), LPPAI (−2.3 points, SD 1.1, p=0.002) and Skindex-16 (−21.0 points, SD 22.1, p=0.014) scores at week 24. Bulk transcriptomic analysis of untreated LPP revealed upregulation of type I Interferon (IFN)-stimulated genes and pathways related to inflammation, immune activation, keratinization, and extracellular matrix remodelling, with downregulation of immune and inflammatory pathways following treatment. Single-cell RNA-seq of LPP was characterized by enrichment of CD8+GZMK+ T cells which showed downregulation of T-cell receptor signaling as well as antiviral pathways with treatment. Basal keratinocytes exhibited reduced cytokine and interferon signaling and decreased communication with NK cells following treatment. CCL19+ fibroblasts were prominent in untreated disease was attenuated after treatment, with downregulation of type I IFN signaling. Selective TYK2 inhibition with deucravacitinib effectively suppresses these inflammatory circuits in LPP and represents a promising therapeutic strategy.

Abstract Objectives Diagnosing adult T-cell leukemia/lymphoma (ATLL) remains challenging due to its clinical and histopathologic heterogeneity. While HTLV-1 serology is a key diagnostic criterion, it is often unavailable at the time of diagnosis and does not confirm viral integration in tumor cells. The HTLV-1–encoded HBZ RNA is a reliable diagnostic biomarker for ATLL. We evaluated the diagnostic performance of RNAscope in situ hybridization (ISH) for HBZ RNA in formalin-fixed, paraffin-embedded (FFPE) tissues to distinguish ATLL from other T-cell lymphomas. Methods HBZ ISH was evaluated in 72 cases, including 52 ATLLs and 20 non-ATLL T-cell lymphomas, to determine diagnostic sensitivity and specificity, interobserver agreement, interlaboratory reproducibility, and comparison with digital gene expression. Results This assay demonstrated 86.5% sensitivity and 100% specificity, with sensitivity improving to 97% when excluding bone marrow clot sections and FFPE blocks older than 5 years. Interobserver agreement among 3 pathologists was excellent (κ = 0.92, percent agreement: 94%). Interlaboratory reproducibility of HBZ ISH was high, with 93% to 95% concordance across these Clinical Laboratory Improvement Amendments–certified laboratories. HBZ RNA ISH–positive cases demonstrated significantly higher HBZ gene expression levels by digital gene expression profiling. Conclusions We established HBZ ISH as a reliable tissue-based surrogate for HTLV-1 infection in ATLL. This assay will enhance diagnostic accuracy, expedite definitive diagnosis, and improve patient selection for targeted therapies and clinical trials, particularly in regions with a high prevalence of HTLV-1.

Abstract Cutaneous squamous cell carcinoma (cSCC) poses significant clinical challenges due to its rising incidence and potential for metastasis. Histopathologic risk stratification is further limited by substantial inter-observer variability. Unsupervised AI approaches based on content-based image retrieval offer scalable and interpretable decision support for diagnostic pathology. The objective of this study was to evaluate the use of image retrieval within histopathology atlases to stratify cSCC tumor differentiation from whole-slide images (WSIs), while comparing different patch selection and feature extraction strategies. This retrospective study included 552 archived WSIs comprising 385 well-differentiated, 102 moderately differentiated, and 66 poorly differentiated cases collected across Mayo Clinic sites in Arizona, Florida, and Minnesota. Image atlases were constructed using multiple patch aggregation strategies (Mosaic, Collage, and Montage) and deep learning encoders (KimiaNet, PathDino, and H-Optimus-0). A leave-one-WSI-out evaluation framework was used to assess differentiation classification performance using accuracy, specificity, sensitivity, and F1 score. Mosaic combined with KimiaNet achieved the highest Top-1 accuracy (74.9%) and specificity (92.6%), while Mosaic with H-Optimus-0 yielded the best Top-5 accuracy (79.0%) and macro-F1 score (62.6%). Collage combined with KimiaNet produced the highest Top-5 specificity (99.5%). The generalizability of the evaluated AI models varied across hospitals, reflecting differences in imaging protocols, staining practices, and patient populations. Overall, unsupervised image search and retrieval provides effective, annotation-free support for cSCC differentiation and has the potential to enhance dermatopathology workflows when appropriate combinations of patch selection and feature ex-traction methods are employed.

Evaluation of T-cell receptor (TCR) β-chain constant region 1 (TRBC1) expression is an alternative T-cell clonality assessment method. However, evaluation of TRBC1 immunohistochemistry (IHC) for distinguishing mycosis fungoides (MF)/Sezary syndrome (SS) from reactive inflammatory infiltrates in skin is incomplete. We evaluated the utility of a novel dual TRBC1-CD3 IHC stain in skin biopsies with MF/SS (n=40), reactive (n=24), or atypical T-cell infiltrates indeterminant for MF/SS (n=9). Twenty of 24 reactive cases showed clear polytypic TRBC1 expression (median percent TRBC1 positivity among CD3-positive T cells [%TRBC1+] 50% in dermis, 42.5% in epidermis among all cases), while 34/40 MF/SS were clearly monotypic (%TRBC1+ either ≤20% or ≥85%) (sensitivity 85.0%, specificity 91.7%, positive predictive value 94.4%, negative predictive value 78.6%). Discordance between TRBC1 expression and diagnosis was associated with few neoplastic/monotypic T cells and/or lack of physical separation between neoplastic and non-neoplastic populations. Among patch/plaque MF/SS, TRBC1 showed similar diagnostic sensitivity (80.0% vs. 86.7%) and high categorical correlation (monotypic vs. not monotypic, 80%) with TCR gene rearrangement results. TRBC1 interpretation was reproducible, with ≥2/3 and 3/3 pathologists rendering identical interpretations in 100% and 86% of cases, respectively, after independent review and 100% agreement following collective review. Digital image analysis confirmed visual %TRBC1+ accuracy ( r =0.9749, P <0.0001). On the basis of these results, we propose %TRBC1+ cutoffs of <25% or >75% for establishing T-cell monotypia in skin. Considering such thresholds, TRBC1-CD3 evaluation facilitated diagnostic refinement in 7/9 (78%) atypical cases. Overall, TRBC1-CD3 IHC clearly and rapidly aids diagnosis of cutaneous T-cell proliferations.

Background: Rheumatoid arthritis is a relatively common rheumatic disease that can present with inflammatory arthritis and subcutaneous nodules. Multicentric reticulohistiocytosis and fibroblastic rheumatism are rarer entities that also present with these features. Methods: Two cases, one of each of fibroblastic rheumatism and multicentric reticulohistiocytosis, are described highlighting characteristic clinical, radiographic, and histologic findings. A narrative review of the literature on these rarer conditions, compared with rheumatoid arthritis, is provided with a focus on articular and cutaneous findings, available information on disease presentations, and key contrasting features that can aid in diagnosis. Results: Radiographic erosion distribution and joint space narrowing, clinical nodule distribution and characteristics, and nodule histology can differ between these diseases. Conclusions: Multicentric reticulohistiocytosis and fibroblastic rheumatism should be considered in the evaluation of seronegative rheumatoid arthritis, especially in cases that do not respond predictably to standard therapies, and cutaneous nodule biopsy can aid in differentiating these three conditions.

BACKGROUND Cutaneous lichen planus (LP) is a recalcitrant, difficult-to-treat, inflammatory skin disease characterized by pruritic, flat-topped, violaceous papules on the skin. Baricitinib is an oral Janus kinase (JAK) 1/2 inhibitor that interrupts the signaling pathway of IFN-γ, a cytokine implicated in the pathogenesis of LP. METHODS In this phase II trial, 12 patients with cutaneous LP received 2 mg daily baricitinib for 16 weeks, accompanied by in-depth spatial, single-cell, and bulk transcriptomic profiling of pre- and posttreatment samples. RESULTS An early and sustained clinical response was seen, with 83.3% of patients responsive at week 16. Our molecular data identified a unique, oligoclonal IFN-γ, CD8 + , and CXCL13 + cytotoxic T cell population in LP skin and demonstrated a rapid decrease in IFN signature within 2 weeks of treatment, most prominently in the basal layer of the epidermis. CONCLUSION This study demonstrates the efficacy and molecular mechanisms of JAK inhibition in LP. TRIAL REGISTRATION NCT05188521 FUNDING Eli Lilly, Appignani Benefactor Funds, 5P30AR075043, Mayo Clinic Clinical Trials Stimulus Funds.

AbstractBackgroundTechnology has revolutionized not only direct patient care but also diagnostic care processes. This study evaluates the transition from glass‐slide microscopy to digital pathology (DP) at a multisite academic institution, using mixed methods to understand user perceptions of digitization and key productivity metrics of practice change.MethodsParticipants included dermatopathologists, pathology reporting specialists, and clinicians. Electronic surveys and individual or group interviews included questions related to technology comfort, trust in DP, and rationale for DP adoption. Case volumes and turnaround times were abstracted from the electronic health record from Qtr 4 2020 to Qtr 1 2023 (inclusive). Data were analyzed descriptively, while interviews were analyzed using methods of content analysis.ResultsThirty‐four staff completed surveys and 22 participated in an interview. Case volumes and diagnostic turnaround time did not differ across the institution during or after implementation timelines (p = 0.084; p = 0.133, respectively). 82.5% (28/34) of staff agreed that DP improved the sign‐out experience, with accessibility, ergonomics, and annotation features described as key factors. Clinicians reported positive perspectives of DP impact on patient safety and interdisciplinary collaboration.ConclusionsOur study demonstrates that DP has a high acceptance rate, does not adversely impact productivity, and may improve patient safety and care collaboration.

Reactive granulomatous dermatitis (RGD) is an umbrella term to describe a reaction pattern characterized by skin-colored to erythematous papules, plaques, and nodules although other morphologies have been described. RGD has rarely been reported in children, and in this report, we present the case of a 3-year-old girl with acute lymphoblastic leukemia (ALL) who presented with firm, tender nodules, and ulcerated plaques on her extremities. Histopathologic examination showed foci of dense granulomatous inflammatory infiltrates composed of histiocytes, neutrophils, and multinucleate giant cells. The constellation of clinical symptoms, negative infectious workup, and histopathology support the diagnosis of RGD.