Dermatology: Practical and Conceptual Dermatology Practical & Conceptual Introduction Primary cutaneous B-cell lymphoma (PCBCL) is a lymphopro- liferative B-cell disorder involving only the skin at the time of diagnosis. PCBCLs comprise a group of rare disease that account for 20%-25% of all cutaneous lymphomas, and they are clas- sified into 3 main types: (i) follicle center lymphoma (the most common and usually indolent), (ii) marginal zone lymphoma, and (iii) diffuse large B-cell lymphoma (the most aggressive) [1]. Case Presentation We present the case of a 63-year-old otherwise healthy Cau- casian woman who sought consultation at our skin cancer department for a cluster of lesions localized on the right cheek, presenting as pinkish-erythematous, slow-growing, firm nodules, irregularly oval in shape, with well-defined borders, that had been enlarging over the past 8 years. The largest nodule was 30 mm in diameter (Figure 1A). The patient denied correlation with traumas or arthropods bites and felt no local pain or itch. No other cutaneous lesions were found at total-body checkup. Systemic involvement was ruled out with laboratory tests, ultrasound examination of lymph node stations, and computed axial tomography of chest and abdomen. Dermoscopic evaluation (×20; DermLite, 3Gen) showed the presence of an erythematous background with salm- on-colored areas, arborizing vessels, and peculiar yellow plugs surrounded by well-defined white circles (Figure 1B). The integration of the clinical history and information pro- vided by dermoscopy led to the hypothesis of B-cell lym- phoma. A 5-mm punch biopsy was performed, and the histopathological report confirmed the clinical diagnosis of cutaneous B-cell lymphoma, follicle center subtype. Research Letter | Dermatol Pract Concept. 2022;12(1):e2022006 1 Yellow Plugs: An Additional Dermoscopic Criterion in the Diagnosis of Primary Cutaneous B-Cell Lymphoma Claudio Conforti1, Roberta Giuffrida2, Arianna Dri1, Iris Zalaudek1, Nicola Di Meo1 1 Dermatology Clinic, Maggiore Hospital, University of Trieste, Trieste, Italy 2 Department of Clinical and Experimental Medicine, Dermatology, University of Messina, Italy Key words: cutaneous lymphoma, dermoscopy, lymphomas, diagnosis Citation: Conforti C, Giuffrida R, Dri A, Zalaudek I, Di Meo N. Yellow plugs: an additional dermoscopic criterion in the diagnosis of primary cutaneous b-cell lymphoma. Dermatol Pract Concept. 2022;12(1):e2022006. DOI: https://doi.org/10.5826/dpc.1201a06 Accepted: April 25, 2021; Published: January 2022 Copyright: ©2022 Conforti 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: Roberta Giuffrida, MD, Department of Clinical and Experimental Medicine, Dermatology, University of Messina, Messina, Italy. Email: roberta_giuffrida@hotmail.it 2 Research Letter | Dermatol Pract Concept. 2022;12(1):e2022006 Figure 1. (A) Clinical image of the follicle center of PCBCL: pinkish-erythematous firm nodules, irregularly oval in shape, with well-defined borders, located on the cheek. (B) Dermoscopy of the follicle center of PCBCL: erythematous background, salmon-colored areas, arborizing vessels, and yellow plugs surrounded by well-defined white circles. Figure 2. (A) Tissue fragment of PCBCL obtained by punch biopsy (standard H&E, magnification ×10). (B) Histopatho- logical picture of the lymphoma: nodular lymphoid infiltrates arranged in a follicular pattern in the dermis (standard H&E, magnification ×20). Conclusions Overall, PCBCLs may clinically appear as papules, plaques, or nodules of different shapes, number, colors, and body locations. Differential diagnosis includes a wide spectrum of pathologies, such as basal cell carcinoma, amelanotic melanoma, arthropod bite scar, or keloid, and for this rea- son a skin biopsy is always needed to arrive at the correct diagnosis, even if dermoscopy can help rule out other skin disorders [2]. Currently available literature states that white circles and salmon-colored areas are the main common dermoscopic features of PCBCLs. Regarding vascularization, arborizing or serpentine vessels could be found, sometimes simultaneously, resulting in a polymorphous vascular pattern. Scales are a further criterion highlighted in a retrospective study [3-5]. Research Letter | Dermatol Pract Concept. 2022;12(1):e2022006 3 The presence of yellow plugs dermoscopic examination of PCBCLs have yet to be reported. In our patient, yellow plugs were detectable throughout the entire lesion, and particularly evident in the central area. The term “yellow plugs” refers to yellow structures surrounded by white circles combined with an erythematous background with salmon-colored areas and arborizing ves- sels. The histopathological examination described nodular lymphoid infiltrates arranged in a follicular pattern in the dermis. The follicles were atypical because of the absence of polarization and mantle and showed a reduction in the num- ber of macrophages (Figure 2, A and B). The cell immuno- phenotypic patterns were CD20+, Bcl-6+, CD10+ and partial Bcl-2+. There was no evidence of adnexal involvement, so it can be assumed that the accentuated follicular plugging was the result of the upward displacement of the epidermis by the underlying conspicuous dermal infiltrate. Although dermoscopy cannot replace the histopatho- logical examination, the combination of an erythematous background, salmon-colored areas, white circles, arborizing vessels and/or scales, as previously reported by other authors, as well as peculiar yellow plugs, may be helpful in consider- ing PCBCLs in the differential diagnosis of cutaneous pink nodules. The peculiar features listed can help in promptly suspecting a possible lymphoma and in identifying the correct site for biopsy. Moreover, dermoscopy can be used to monitor recurrences. Since PCBCLs comprise a group of rare diseases, further investigations are needed to deepen the knowledge on the subject. Informed consent: Written informed consent for pub- lication of her clinical details and clinical images was obtained from the patient. References 1. Willemze R, Cerroni L, Kempf W, et al. The 2018 update of the WHO-EORTC classification for primary cutaneous lym- phomas. Blood. 2019;133(16):1703-1714. DOI: 10.1182/ b l o o d - 2 0 1 8 - 1 1 - 8 8 1 2 6 8 . P M I D : 3 0 6 3 5 2 8 7 . P M C I D : PMC6473500. 2. Conforti C, Giuffrida R, Vezzoni R, Resende FSS, di Meo N, Zalaudek I. Dermoscopy and the experienced clinicians. Int J Der- matol. 2019 Jun 20. DOI: 10.1111/ijd.14512. PMID: 31222814. 3. Mascolo M, Piccolo V, Argenziano G, et al. Dermoscopy pat- tern, histopathology and immunophenotype of primary cuta- neous b-cell lymphoma presenting as a solitary skin nodule. Dermatology. 2016;232(2):203-207. DOI: 10.1159/000442251. PMID: 26694025. 4. 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