Untitled Quiz | Dermatol Pract Concept 2015;5(4):2 5 DERMATOLOGY PRACTICAL & CONCEPTUAL www.derm101.com The patient A 72-year-old man presented to our clinic with a 12-month history of a new, growing, asymptomatic, pigmented flat lesion on his right leg. The physical examination revealed an irregular, dark-brown patch with 8 mm of maximum diameter (Figure 1). A pigmented flat lesion on the leg of a 72-year-old man Virgínia Coelho de Sousa1, André Oliveira1 1 Department of Dermatology, Hospital de Santo António dos Capuchos - Centro Hospitalar de Lisboa Central, Lisboa, Portugal Key words: clonal seborrheic keratosis, dermoscopy, melanoma Citation: Coelho de Sousa V, Oliveira A. A pigmented flat lesion on the leg of a 72-year-old man. Dermatol Pract Concept 2015;5(4):2. doi: 10.5826/dpc.0504a02 Copyright: ©2015 Coelho de Sousa et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Corresponding author: André Oliveira, MD, Department of Dermatology, Hospital de Santo António dos Capuchos - Centro Hospitalar de Lisboa Central, Alameda Santo António dos Capuchos, 1169-050, Lisboa, Portugal. Tel. +351912561666; Fax. +351213562208. Email: andre.oliveira@sapo.pt Figure 1. An irregular, dark-brown patch with 8 mm. [Copyright: ©2015 Coelho de Sousa et al.] Figure 2. Multiple small and loosely arranged brown globules (blue circles) resembling the so-called dermoscopic “concentric struc- tures.” [Copyright: ©2015 Coelho de Sousa et al.] Dermoscopy disclosed a sharply demarcated lesion corre- sponding to the jelly-sign (red arrows). Additionally, multiple small and loosely arranged brown globules (blue circles) resembling the so-called dermoscopic “concentric structures,” were seen (Figure 2). A punch biopsy of the lesion was performed. Histopatho- logical examination revealed multiple heavily pigmented intra-epidermal nests of basaloid cells, corresponding to the Borst-Jadassohn phenomenon (Figure 3, hematoxylin & eosin [H&E], x200). What is your diagnosis? 6 Quiz | Dermatol Pract Concept 2015;5(4):2 of clinical simulators of melanoma [2]. Described criteria for melanocytic and non-melanocytic lesions are sometimes seen together in the same lesion [3]. Common dermoscopic features of SK include fissures and ridges, comedo-like open- ings, milia-like cysts and sharply demarcated borders [4,5]. Clonal SK is considered a rare variant characterized by proliferation of intra-epidermal clusters of basaloid cells known as Borst-Jadassohn phenomenon. Dermoscopic fea- tures of clonal SK have previously been documented in few reports or small case series [6-10]. In our case, the patient’s history pointed towards the diagnosis of melanoma. How- ever, jelly-sign favored a SK even if milia-like cysts and other frequently observed criteria were absent. Globular structures are observed mainly in melanocytic tumors. Clonal SK, basal cell carcinoma and epidermal nevi are few of the known exceptions. In the former, globules correspond to the epider- mal nests of pigmented basaloid cells seen in histopathology. In conclusion, clonal SK represents a dermoscopic pitfall being difficult to differentiate from melanoma. Both tumors are also increasingly more prevalent in the elderly. Histo- pathological examination should always be performed in such confounding lesions. References 1. Hafner C, Vogt T. Seborrheic keratosis. J Dtsch Dermatol Ges. 2008;6:664-77. 2. Argenziano G, Soyer HP, Chimenti S, et al. Dermoscopy of pig- mented skin lesions: result of a Consensus Meeting via Internet. J Am Acad Dermatol. 2003;48:679-93. 3. Argenziano G, Rossiello L, Scalvenzi M, et al. Melanoma simu- lating seborrheic keratosis: a major dermoscopy pitfall. Arch Dermatol. 2003;139:389-91. 4. Braun RP, Krischer J, Saurat JH. The “wobble” sign in epilumi- nescence microscopy as a novel clue to the differential diagnosis of pigmented skin lesions. Arch Dermatol. 2000;136:940-42. 5. Longo C, Moscarella E, Piana S, et al. Not all lesions with a ver- rucous surface are seborrheic keratoses. J Am Acad Dermatol. 2014;70:e121-3. 6. Longo C, Zalaudek I, Moscarella E, et al. Clonal seborrheic kera- tosis: dermoscopic and confocal microscopy characterization. J Euro Acad Dermatol Venereol. 2013;28:1397-400. 7. Zalaudek I, Ferrara G, Argenziano G. Clonal seborrheic keratosis: a dermoscopic pitfall. Arch Dermatol. 2004;140:1169-70. 8. Popadic M. A hyperkeratotic clonal seborrheic keratosis ac- companied by nodulocystic basal cell carcinoma. J Am Acad Dermatol. 2015;72:e113-5. 9. Fraga-Braghiroli NA, Merati M, Rabinovitz H, Scope A. Re- flectance confocal microscopy features of a clonal seborrheic keratosis that clinically and dermoscopically simulates melanoma. Dermatol Surg. 2015;41:662-5. 10. Yagerman SE, Marghoob AA. Clonal seborrheic keratosis versus epidermal nevus. J Am Acad Dermatol. 2013;69:e43-4. Diagnosis Clonal seborrheic keratosis Clinical course As it is considered a benign non-melanocytic lesion, a con- servative management was proposed. No further unnecessary therapeutic procedures were performed. Answer and explanation Seborrheic keratosis (SK) is one of the more common skin neoplasms seen by dermatologists. Clinical and dermoscopic diagnosis of SK is straightforward in most of the cases. However, deeply pigmented lesions can resemble melanoma. SK may be grouped into seven histological subtypes, with acanthotic, hyperkeratotic and adenoid variants being the more representative [1]. Dermoscopy is a fast, non-invasive technique that increases diagnostic accuracy for both melanocytic and non- melanocytic skin tumors, allowing for a better differentiation Figure 3. Histopathological examination revealed Borst-Jadassohn phenomenon (H&E, x200). [Copyright: ©2015 Coelho de Sousa et al.]