Gordana Štajminger

Jaka Radoš

Jasna Lipozenčić

Zrinjka Paštar

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24    Regressing Seborrheic Keratosis – Clinically and Dermoscopically Mimicking a Regressing MelanomaZrinjka Paštar1, Jasna Lipozenčić2, Jaka Radoš2, Gordana Štajminger3 1Health Department, Ministry of Defense, Republic of Croatia; 2University Department of Dermatology and Venereology, Zagreb University Hospital Center; 3Private Clinic for Internal Medicine “Dr. Gordana Štajminger”, Opatička 8, Zagreb, Croatia Corresponding author:Zrinjka Paštar, MDHealth Department, Ministry of DefenseČerinina 23HR-10000 ZagrebCroatiazpastar@hi.htnet.hrReceived: December 11, 2006.Accepted: January 28, 2007.SUMMARY The diagnosis of seborrheic keratosis is a clinical diagnosis. In a certain percentage of cases, differential diagnosis between seborrheic keratosis and malignant melanoma is difficult. We describe a case of regressing seborrheic keratosis simulating malignant melanoma. Clinical, dermoscopic and histopathologic examinations were performed for the occurrence of an asymmetric, irregularly demarcated, irregularly pigmented lesion measuring 1.3 x 1.5 cm on the right part of the abdomen in a 76-year-old male Caucasian. In order not to miss melanoma, the excision and histopathologic examination of the lesion with peppering is essential.KEY WORDS: regressing seborrheic keratosis, regressing melanoma, dermoscopyINTRODUCTION Dermoscopy is a simple, noninvasive, in vivo method improving the sensitivity and specificity of clinical diagnosis of pigmented skin lesions. The first step of dermoscopic pattern analysis is to differentiate melanocytic from nonmelanocytic le-sions (1,2). Diagnosis of seborrheic keratosis (SK) is a clinical diagnosis but in a certain percentage of cases, differential diagnosis between SK and ma-lignant melanoma is difficult. The most important dermoscopic criteria for SK are comedo-like pseu-dofollicular openings and horn pseudocysts (3-5). Flat SK on the face shows pseudopigmented net-work formed by follicular openings but asymmetric follicular openings are not seen (3). However, in some cases, there are overlapping dermoscopic features that may present significant pitfall in differentiation of melanocytic lesions from nonmelanocytic lesions (6).  We report on a case of a completely regressing seborrheic keratosis (RSK) simulating melanoma.CASE REPORT  We report on a 76-year-old man with a history of numerous SKs and two basal cell carcinomas, who presented with a pigmented suspect lesion on the right part of the abdomen without a known his-tory of duration. Clinically, on the right part of the abdomen there was an asymmetric, irregularly de-marcated, irregularly pigmented lesion measuring 1.3 x1.5 cm. On the right part of the lesion, there was a slightly elevated dark brown area. Centrally and on the left part of the lesion there were light, dark brown and white-bluish areas (Fig. 1).  From the clinical point of view, the lesion ap-peared suspect as it complied with all the ABCDE criteria for the diagnosis of melanoma.  On dermoscopy, two distinctive parts were no-ticed (Fig. 2). In the right part of the lesion, numer-ous milia-like cysts on the background of brown diffuse pigmentation with brown-bluish peppering were seen. In the central and left part of the lesion a regressive area with brown-bluish peppering Acta Dermatovenerol Croat             2007;15(1):24-26                                     CASE REPORT25ACTA DERMATOVENEROLOGICA CROATICAeffect and brown diffuse pigmentation was seen. No comedo-like openings were observed in the le-sion. The patient was in good general health with hy-pertension in personal history. Physical examina-tion revealed no lymphadenopathy. Ultrasonogra-phy of regional lymph nodes was within the normal limits. As confident exclusion of regressing melanoma could not be made on the basis of both clinical and dermoscopy findings, the excision was done. His-topathologic examination revealed mild hyperker-atosis, acanthosis, proliferation of basaloid cells, slight melanocytic hyperplasia, abundant pigment in the basaloid cells, melanocytes engorged with melanin, and horn pseudocysts (Fig. 3). In the other part, atrophic epidermis, slight vacuolar de-generation of basaloid cells, scant melanophages, and mild lymphohistiocytic infiltration throughout the papillary dermis were observed (Figs. 4 and 5). Therefore, the diagnosis of completely RSK was made.  Figure 1. On the right part of the abdomen there was an asymmetric, irregularly demarcated, irreg-ularly pigmented lesion measuring 1.3 x 1.5 cm. On the right part of the lesion there was a slightly elevated dark brown area. Centrally and on the left part of the lesion there were light, dark brown and white-bluish areas.Figure 2. In the right part of the lesion, numerous milia-like cysts on a background of brown diffuse pigmentation with brown-bluish peppering were seen. In the central and left part of the lesion, a regressive area with brown-bluish peppering and brown diffuse pigmentation was seen.Figure 3. Mild hyperkeratosis, acanthosis, pro-liferation of basaloid cells, slight melanocytic hy-perplasia, abundant pigment in the basaloid cells, melanocytes engorged with melanin and horn pseudocysts. (H&E staining, original magnifica-tion X40)DISCUSSION Clinically, SK is a simulator of melanoma (7,8). In our case, the dermoscopy finding of diffuse pig-mentation and milia-like pseudocysts correlated histopathologically with abundant pigment in the basaloid cells, melanocytes engorged with mela-nin, acanthotic epidermis and intraepidermal ker-atin-filled cysts, while peppering effect correlated histopathologically with scant melanophages in papillary dermis. These scant melanophages were found equally throughout the lesion. The changes with brown-bluish peppering effect could be a li-chen planus-like keratosis (LP-LK). LP-LK is thought to be a regressing solar len-tigo or seborrheic keratosis (9). Histologically, it represents a lichenoid reaction to a pre-existing solar lentigines or seborrheic keratosis. It is most commonly seen as a single lesion on the upper extremities, face and chest (3,9). It usually has a history of a preceding pigmented macule/plaque Paštar et al.     Acta Dermatovenerol CroatRegressing seborrheic keratosis      2007;15(1):24-26 26 ACTA DERMATOVENEROLOGICA CROATICA(solar lentigo or seborrheic keratosis), often rap-idly changes, and is pruritic (with a range of other abnormal sensations) (9). A common dermoscopic presentation is an area of multiple blue-gray dots or peppering on a uniform tan background (9,10). Biopsy specimens in our case did not reveal a band-like infiltrate of mononuclear cells, therefore the diagnosis of LP-LK was rejected. Moreover, peppering is commonly seen in association with histological regression and therefore can be seen in any pigmented lesion (9). However, since re-gression may be a feature of malignant melanoma, the presence of peppering is a significant feature of invasive melanoma (9). On the other hand, in regressing melanoma one would expect residual tumor and abundant melanophages.  Therefore, the diagnosis of the completely RSK with peppering was established. CONCLUSION We emphasize that peppering is a common dermoscopic finding in all pigmented lesions with regression including SK, LP-LK, and melanoma. Therefore, in order not to miss melanoma, exci-sion and histopathologic examination of these le-sions are essential.References1.   Soyer HP, Argneziano G, Chimenti S, Men-zies SW, Pehamberger H, Rabinowitz HS, et al. Dermoscopy of pigmented skin lesions: an atlas based on the Consensus Net Meeting on Dermoscopy 2000. Milan: Edra Medical Pu-blishing and New Media, 2001.2.   Argenziano G, Soyer HP, Chimenti S, Talamini R, Corona R, Sera F, et al. Dermoscopy of pig-mented skin lesions: results of a consensus meeting via the Internet. J Am Acad Dermatol 2003;48:679-93.3.   Stolz W, Braun-Falco O, Bilek P, Landthaler M. Color atlas of dermoscopy. 2nd enlarged and completely revised edition. Berlin: Blackwell Wissenschaft; 2002.4.   Braun RP, Rabinovitz HS, Krischer J, Kreusch, Oliviero M, Naldi L, et al. Dermoscopy of pig-mented seborrheic keratosis: a morphological study. Arch Dermatol 2002;138:1556-60.5.   Braun RP, Rabinovitz HS, Oliviero M, Kopf AW, Saurat JH. Dermoscopic diagnosis of seborr-heic keratosis. Clin Dermatol 2002;20:270-2.6.    De Giorgi V, Massi D, Stante M, Carli P. False “melanocytic” parameters shown by pigmen-ted seborrheic keratoses: a finding which is not uncommon in dermoscopy. Dermatol Surg 2002;28:776-9.7.   Braun-Falco O, Plewig G, Wolff HH, Burgdorf WHC. Benign epithelial tumors. In: Braun-Fal-co O, Plewig G, Wolff HH, Burgdorf WHC, eds. Dermatology, 2nd completely revised edition. Berlin: Springer; 2000.p.1441-8. 8.   Rossielo L, Zalaudek I, Ferrara G, Do-cimo G, Giorgio CM, Argenziano G. Mela-noacanthoma simulating pigmented spitz nevus: an unusual dermoscopy pitfall. Dermatol Surg 2006;32:735-7.9.   Menzies SW, Crotty KA, Ingwar C, McCarthy WH. An atlas of surface microscopy of pig-mented skin lesions: dermoscopy. Sydney: McGraw-Hill:  2003. 10. Wang SQ, Katz B, Rabinovitz H, Kopf AW, Oliviero M, Rao BK. Lessons on dermoscopy: case #10. Dermatol Surg 2000;26:1079-80.Figure 4. Atrophic epidermis, slight vacuolar de-generation of basaloid cells, scant melanophages and mild lymphohistiocytic infiltrate were seen symmetrically throughout the papillary dermis. (H&E staining, original magnification X40)Figure 5. A detail from Figure 5. (H&E staining, original magnification X120)Paštar et al.     Acta Dermatovenerol CroatRegressing seborrheic keratosis      2007;15(1):24-26 

Regressing Seborrheic Keratosis - Clinically and Dermoscopically Mimicking a Regressing Melanoma

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