Seborrheic keratosis that resemble melanoma

Received on: 14/06/2011
Approved on: 18/06/2011

This study was carried out at the Faculdade
de Medicina do ABC (FMABC) – Santo André
– (SP), Brazil.

Conflicts of interests: none
Financial support: none

Abstract

Seborrheic keratosis are benign epithelial tumors that are usually easily diagnosed through clinical and dermatoscopic examination. They can sometimes resemble malignant lesions, especially melanoma. This article illustrates two such cases, highlighting the detailed dermatoscopic observations that help distinguish these lesions, to help increase the accuracy of diagnoses.

Keywords: KERATOSIS, SEBORRHEIC, MELANOMA, DERMOSCOPY

Seborrheic keratosis is a benign epithelial tumor that is formed by epidermal proliferation at the expense of basaloid cells, which can be pigmented. It is more common from the age of 50 and in Caucasians. 1 Its etiology is unknown, but it may run in families and be influenced by growth factors. 1

Clinically, it manifests as a plaque or papule with a waxy appearance, usually brownish and well delimited, which can manifest in any area of the skin especially in photoexposed areas, excluding the palmoplantar region.

During dermatoscopy, it is mainly characterized by milia- like cysts (round and yellowish intraepidermal formations filled with keratin) and comedo-like openings (chestnut brown-black invaginations, filled with keratin and with well defined borders). 2, 3 Although those characteristics can also be observed in papillo- matous melanocytic nevi, they are very common in seborrheic keratoses. Other verifiable traits are moth-eaten or jelly borders in plane lesions, and a cerebriform aspect in more papulous ones.

Its diagnosis does not usually present difficulties, although in some situations it can simulate melanoma in the clinical and dermatoscopic examinations. 2 Therefore a histological study is required to confirm the diagnosis in such cases. The article dis- cusses cases that characterize seborrheic keratoses resembling melanoma.

Case 1:
A 69-year-old female Asian patient presented an irregular pigmented lesion in the lumbar region, with no other similar lesions on the skin. She could not specify for how long she had had it and'''''''' did not have a history of melanoma. In the dermatoscopic examination, the lesion appeared asymmetric, with pig- mentation varying from light to dark brown, forming an amor- phous area, with a delicate pigmentary network in most of the lesion and an area of eccentric hyperpigmentation where the pigmentary network was thicker and there were blotches. Due to the possibility of melanoma, an excisional biopsy was performed, with the histopathologic examination results determining that it was a pigmented seborrheic keratosis (Figures 1 and 2).

Case 2:
A 63-year-old white female patient presented with a blackened irregular lesion on the back that she noticed three months previously. She described a family history of skin can- cer, without specifying the type. In the dermatoscopic examina- tion, the asymmetry of the lesion was clear not only regarding the shape, but also the variability of colors (light brown, dark brown, black, grayish and bluish white). Irregular points, blotch- es and a bluish-white veil were observed. Due to a strong suspi- cion of melanoma, a decision was made to carry out an excisional biopsy of the lesion. The histological diagnosis was that the lesion was a seborrheic keratosis (Figure 3 and 4).

COMMENTS

Dermatoscopy, or microscopy epiluminescence, is a non- invasive and practical examination that emerged a few decades ago as an important subsidiary tool in diagnosing pigmented lesions. This method helps differentiate non-melanocytic and melanocytic lesions (first-level analysis), and can gauge the malignant potential of the latter (second-level analysis). It can increase the accuracy of a diagnosis by 5-30%, 2 compared to a clinical examination alone. However, in certain situations there are difficulties in interpreting the results due to features that get mixed and the subjective nature of the analysis, which could lead to false-positive or false-negative results for malignancy – especially in the case of melanoma. 4

This article is aimed at illustrating some of those situations, describing seborrheic keratosis cases that resemble melanoma, both clinically and dermoscopically.

First-level analysis is the most important in identifying seb- orrheic keratosis. If the lesion is mistakenly found to be melanocytic, there is a high risk of misinterpretation in the sec- ond-level analysis, which can often lead to an erroneous classi- fication of malignancy. 2

The main dermatoscopic features observed in seborrheic keratoses are milia-like cysts and comedo-like openings (initial algorithm proposed by Stolz and colleagues), with well defined moth-eaten or jelly borders. Nonetheless, other features, such as hairpin vessels, pigmentary network-like structures (usually more prominent, thicker and heterogeneous than the classic pig- mentary network of melanocytic lesions), blotches, points, crusts, fissures (cerebriform aspect), fingerprint-like, whitish veil, in addition to a possible variation in colors (yellow, black, dark brown, light brown, grayish-blue), have been already identi- fied. 3,5 The observation of those additional features can reduce diagnostic mistakes considerably, further improving the accura- cy of this valuable dermatologic resource. 2

References

1 . Siqueira CRS,Miot HA. Inflamação de queratoses seborreicas múltiplas induzida por quimioterapia com gencitabina. An Bras Dermatol. 2009;84(4):410-3.

2 . Braun RP, Rabinovitz HS, Krischer J, Kreusch J, Oliviero M, Naldi L, Kopf AW, Saurat JH. Dermoscopy of pigmented seborrheic keratosis. A morphological study. Arch Dermatol. 2002;138(12):1556-60.

3 . Cabo H. Queratosis seborreica VS melanoma: la dermatoscopia es útil em el diagnóstico deferencial? Arch Dermatol. 2002;52(1):11-5.

4 . Carrera C, Segura S, Palou J, Puig S, Segura J,Marti RM, et al. Seborrheic keratosislike melanoma with folliculotropism. Arch Dermatol. 2007;143(3):373-6

5 . Kopf AW, Rabinovitz H,Marghoob A, Braun RP,Wang S,Oliviero M, et al. "Fat fingers": a clue in the dermoscopic diagnosis of seborrheic keratosis. 2006;55(6):1089-91.