Dermatology: Practical and Conceptual Dermatology Practical & Conceptual Letter | Dermatol Pract Concept. 2021; 11(4):e2021095 1 Clonal Seborrheic keratosis: A Diagnostic Dilemma Satish Udare1, Priyanka Patil1 1 Sparkle Skin & Aesthetic Clinic, Vashi, Navi Mumbai, India Key words: seborrheic keratosis, clonal, dermoscopy Citation: Udare S, Patil P. Clonal seborrheic keratosis: A diagnostic dilemma. Dermatol Pract Concept. 2021; 11(4):e2021095. DOI: https://doi.org/10.5826/dpc.1104a95 Accepted: February 24, 2021; Published: October, 2021 Copyright: ©2021 Udare and Patil. This is an open-access article distributed under the terms of the Creative Commons Attribution License 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: Authors have equally contributed to this publication. Corresponding author: Dr. Priyanka Patil, MBBS, DDV. Sparkle Skin & Aesthetic Clinic, Vashi, Navi Mumbai, india. Email: drpriyankapatil219@gmail.com. Introduction Clonal seborrheic keratosis (SK) is an uncommon histological subtype of seborrheic keratosis which may resemble other benign or malignant lesions [1]. Herein, we highlight the clin- ical and histopathological features of this lesion and review the dermoscopic differential diagnoses. Case Presentation A 65-year-old female presented with an asymptomatic dark colored lesion, that has been gradually increasing in size for the last 30 years on the left side of the lower back. No his- tory of bleeding. No history of any medical illness or family history of skin malignancy. On examination single, well circumscribed, irregularly shaped, hyperpigmented keratotic plaque measuring 3 cm in maximum diameter (Figure 1). No palpable lymph nodes were detected. Dermoscopy showed the presence of bluish black to brown globules of varying size, irregularly distributed, well demarcated borders, and milia-like cysts (Figure 2). The tumor was biopsied. Histo- pathological examination showed epidermal hyperplasia with lamellated and basket weave orthohyperkeratosis with mild papillomatosis dermoscopically corresponding to fissures and ridges. Within the neoplasm two distinct subpopulations of basaloid cells (clones) were detected; one of them presented as a nest within the other (Figure 3). The nests dermoscopi- cally corresponded to the globules. Occasional mitotic figures were seen within these clones. Abundant melanin was present within the nested subpopulation of keratinocytes. Sparse superficial perivascular lymphohistiocytic infiltrate is present. There was no interface change or lichenoid pattern to the infiltrate suggestive of clonal seborrheic keratosis. Immunos- taining was not performed. Electrocautery of the lesion was performed with no relapse after 1 year of follow-up. Conclusion In the dermoscopic differential diagnosis of clonal SK, we must consider Hidroacanthoma Simplex (HS) and its malig- nant variant, epidermal nevus, Pagetoid pigmented Bowen disease, in situ melanoma, and superficial Basal Cell Carci- noma (BCC). Clonal SK, is characterized by variously sized, blue-gray globular-like structures that are aggregated to form short lines or irregularly distributed within the lesion [2]. It can reveal other features suggestive of SK, including 2 Letter | Dermatol Pract Concept. 2021; 11(4):e2021095 demarcated borders, milia-like cysts, comedo-like openings, and the jelly sign. Also, polymorphic vascular component is reported [2]. HS shows white globular structures surrounded by homogenous pigmented lines which are not seen in clonal SK.. Dermoscopy of a pigmented malignant hidracanthoma simplex arising from a HS reveals vessels in a conspicuous and irregular shape whereas in clonal SK glomerular, hair- pin and dotted vessels are seen [3]. Epidermal nevus reveals large brown circles. In pagetoid pigmented Bowen disease, glomerular vessels, scaly surface, small brown globules regu- larly packed in a patchy distribution, and a grey homogenous pigmentation are seen. BCC has other characteristics such as arborizing vessels and maple leaf areas while coiled vessels are characteristic of melanoma. The distinction between clonal SK and other benign or malignant lesions is challenging on dermoscopy. Histo- pathological examination will lead to accurate diagnosis in doubtful cases. References 1. Bouhamed M, Bacha D, Abdelmoula F, Slama SB, Lahmar A, Bouraoui S, Sabeh MR. Clonal seborrheic keratosis: a rare skin tumor. Pan Afr Med J. 2019;34:54. DOI: 10.11604/ p a m j . 2 0 1 9 . 3 4 . 5 4 . 1 3 4 1 5 . P M I D : 3 1 7 6 2 9 2 0 ; P M C I D : PMC6859035. 2. Longo C, Zalaudek I, Moscarella E, Lallas A, Piana S, Pellacani G, et al. Clonal seborrheic keratosis: dermoscopic and confocal microscopy characterization. J Eur Acad Dermatol Venere- ol. 2014;28(10):1397–400. DOI: 10.1111/jdv.12261. PMID: 24033484. 3. Ramyead S, Diaz-Cano SJ, Pozo-Garcia L. Dermoscopy of clonal seborrheic keratosis. J Am Acad Dermatol. 2015;73(2):e47-9. DOI: 10.1016/j.jaad.2015.04.013. PMID: 26183995. Figure 1. (A) Clinical presentation of clonal seborrheic keratosis. (B) Dermoscopy reveals the presence of globu- lar-like structures and sharply demarcated borders. Figure 2. Well defined islands of basaloid cell nests within an acan- thotic epidermis (H&E, X40).