Dermatology: Practical and Conceptual 1 Bywaters Lesions: Clinical, Dermoscopic, and Histopathological Insights Sara Salvagno1, Silvia Baravalle1, Chiara Colato2, Antonio Carletto3, Francesco Bellinato1, Giampiero Girolomoni1, Paolo Gisondi1 1 Section of Dermatology and Venereology, Department of Medicine, University of Verona, Verona, Italy 2 Department of Diagnostics and Public Health, Section of Pathology, University of Verona, Verona, Italy 3 Department of Medicine, Rheumatology Operative Unit, AOUI Verona, Verona, Italy Key words: Bywaters lesions, Rheumatoid arthritis Citation: Salvagno S, Baravalle S, Colato C, Carletto A, Bellinato F, Girolomoni G, et al. Bywaters Lesions: Clinical, Dermoscopic, and Histopathological Insights. Dermatol Pract Concept. 2025;15(4):5754. DOI: https://doi.org/10.5826/dpc.1504a5754 Accepted: May 27, 2025; Published: October 2025 Copyright: ©2025 Salvagno et al. This is an open-access article distributed under the terms of the Creative Commons Attribution- NonCommercial License (BY-NC-4.0), https://creativecommons.org/licenses/by-nc/4.0/, which permits unrestricted noncommercial use, distribution, and reproduction in any medium, provided the original authors and source are credited. Funding: None. Competing Interests: None. Authorship: All authors have contributed significantly to this publication. Corresponding Author: Sara Salvagno, Section of Dermatology and Venereology, Department of Medicine, University of Verona, Piazzale A. Stefani 1, Verona 37126, Italy. ORCID ID: 0009-0009-4864-0940. Email: sarasalvagno22@gmail.com Case Presentation A 58-year-old female with a recent diagnosis of seropositive rheumatoid arthritis (RA) treated with methylprednisolone (8 mg/daily) presented with asymptomatic cutaneous lesions on her hands, persisting for two months. Physical examina- tion revealed multiple brown-to-black papules on the prox- imal and lateral nail folds and ventral fingers, with signs of necrosis and fine desquamation (Figures 1A and B). Dermos- copy showed homogeneous structureless brown areas with well-defined borders, mild scaling, and absence of a network and vascular structures (Figures 1C and D). Histopathology demonstrated small vessel vasculitis with focal subintimal fibrinoid necrosis and a perivascular lymphohistiocytic in- filtrate. Areas of collagen necrobiosis bordered by palisading histiocytes were also present, consistent with rheumatoid vasculitis (Figures 1E and F) [1]. Methylprednisolone was suspended, and therapy with etanercept 50 mg weekly and Image Letter | Dermatol Pract Concept. 2025;15(4):5754 acetylsalicylic acid 100 mg/daily was initiated. Complete res- olution was observed at two months. Teaching Point Bywaters lesions are a distinctive cutaneous manifestation of RA. They present as nailfold thromboses and brown- to-black papules on acral surfaces, which correspond to a small vessel lymphocytic/neutrophilic vasculitis, causing intimal obliteration and territorial infarction [2]. Bywaters lesions tend to have a favorable prognosis when occurring in isolation, without requiring specific treatment. Recog- nition of these lesions is clinically relevant as they do not contraindicate the initiation of biologic therapy and are likely to improve with adequate control of the underlying rheumatoid disease. In contrast, the presence of systemic vasculitis may warrant more aggressive immunosuppres- sive management. 2 Image Letter | Dermatol Pract Concept. 2025;15(4):5754 References 1. Magro CM, Crowson AN. The spectrum of cutaneous lesions in rheumatoid arthritis: a clinical and pathological study of 43 patients. J Cutan Pathol. 2003 30(1):1-10. doi: 10.1034/j.1600 -0560.2003.300101.x. PMID: 12534797. 2. Sayah A, English JC 3rd. Rheumatoid arthritis: a review of the cutaneous manifestations. J Am Acad Dermatol. 2005 Aug;53(2):191-209; quiz 210-2. doi: 10.1016/j .jaad.2004.07.023. PMID: 16021111. Figure 1. Multiple brown-to-black papules on the proximal and lateral nailfolds and ventral fingers, with signs of necrosis and fine desquamation (A, B). Homogeneous structureless areas of brownish color, with well-defined bor- ders, without a network and vascular structures, covered by a mild scaly surface (C, D). Small vessel lymphocytic vasculitis with neutrophilic infiltration around the vessel wall (H&E, 40x) (E). Collagen necrobiosis surrounded by histiocytes (H&E, 20x) (F).