Differential Diagnosis of Seborrheic Keratosis: Clinical and Dermoscopic Features

September 2017 | Volume 16 | Issue 9 | Original Article | 835 | Copyright © 2017

Ralph P. Braun MD,a Sabine Ludwig MD,a Ashfaq A. Marghoob MDb

aDepartment of Dermatology, University Hospital Zurich, Zurich, Switzerland bMemorial Sloan Kettering Skin Cancer Center, New York, NY

Abstract

Seborrheic keratosis (SK) is a benign epidermal keratinocytic tumor that is extremely common, particularly in individuals over the age of 50. Most individuals with SK will have more than one lesion and the presence of over 10 lesions in the same person is not uncommon. Although the clinical morphology of most SK with their stuck-on, symmetric, keratotic, and waxy appearance makes them easy to identify, many manifest a morphology resembling melanoma or squamous cell carcinoma. One can argue that such cases will ultimately not prove to be problematic since a simple biopsy will easily reveal their benign nature and eliminate any concerns. However, the cost and morbidity associated with the biopsy of benign lesions should not be underestimated. Methods to improve our in vivo ability to correctly identify SK will prove beneficial not only to the health care system in general but to the individual patient specifically. The issue of greater concern resides with skin cancers that mimic SK or when skin cancers arise in association with SK. Needless to say, in vivo methods to help identify malignancy and differentiate them from benign lesions would be welcomed by all. Fortunately, we do now have in vivo imaging methods such as dermoscopy that can improve the clinician’s diagnostic accuracy. In this article, we summarize the current knowledge regarding the clinical and dermoscopic features of SK, and provide clues to aid in their diagnosis.

J Drugs Dermatol. 2017;16(9):835-842.

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INTRODUCTION

Between 80% and 100% of individuals over the age of 50 have at least one seborrheic keratosis (SK). These lesions may be of concern to the patient by either being aesthetically disturbing or raising anxiety about the possibility of malignancy. Due to these concerns, SK’s are one of the most commonly encountered tumors in a dermatology practice and are also one of the most common benign tumors biopsied to rule out cancer.1-3 Seborrheic keratoses are benign, usually asymptomatic, epithelial tumors that occur mostly on the torso and face; distributed in the so-called seborrheic areas. They usually appear as sharply demarcated waxy brown-to-black plaques with a “stuck-on” appearance. The SK may become increasingly thicker, manifesting a verrucous and rough texture.1 SK’s can also reveal blue-gray colors and irregular borders, and in such lesions, it becomes difficult to exclude the diagnosis of melanoma based solely on naked-eye examination. This becomes increasingly more challenging in the face of an enlarging SK. It is not uncommon for some SK’s to become irritated or in amed and these lesions may resemble skin cancers such as squamous cell carcinoma (SCC).3 Despite the extremely high incidence and prevalence of SK, its etiology, genetic, and molecular profiles are only recently being elucidated. 4-7 It is quite possible that SK hold keys that may unlock knowledge regarding epithelial tumorigenesis. 5,8 Owing to the typical stuck-on and waxy appearance of most SK’s, they are readily recognizable, but some may clinically appear atypical resembling melanoma or SCC. On the one hand, these cases will not prove to be problematic; a biopsy with histological examination easily proves their benign nature. On the other hand, the cost and morbidity associated with this biopsy of benign lesions should not be underestimated. Regarding the medico-economic issues, Duque et al found that the costs associated with treatment for histologically con rmed SK in 1998 was a staggering 38 million US dollars – and that was for Medicare patients alone, excluding all other insurance carriers.9 Methods to enhance the in vivo ability to correctly identify SK will prove beneficial not only to the health care system in general but to the individual patient in particular. The issue of greater concern resides with skin cancers that mimic SK10-13 or when a skin cancer arises in association with a SK.14-17 Fortunately, in vivo imaging methods such as dermoscopy are improving the clinician’s diagnostic accuracy of skin lesions. Here, we summarize the current knowledge regarding the clinical and dermoscopic features of SK and outline key features for their clinical diagnosis.

Clinical Features of Seborrheic Keratosis

Clinical criteria used for diagnosing SK are based on morphology and location of the lesions. SK may occur as an isolated lesion, but most individuals with SK will harbor multiple lesions. In addition, when multiple lesions are encountered in

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