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March 15, 2011 / molehunter

Deeply pigmented seborrhoeic keratosis

Seborrhoeic keratoses, otherwise known as seborrhoeic warts or basal cell papillomas, are very common over the age of 50. They can be any colour from pink to black, most are various shades of brown. They are commonly referred as suspected melanomas because of their dark and variegated colour. The dermoscope is very useful, given some training, at distinguishing them from dangerous pigmented lesions. Here is an example of a very dark and irregular seborrhoeic wart which breaks several ABCDEF rules.

this lesion is very dark, of varied colour, mildly asymmetrical and over 1cm.

dermoscopic view of dark keratosis

to the trained eye, this is an unequivocal seborrhoiec keratosis. See below for annotations of the dermoscopic features.

Annotations: the broad arrows show a very clean, smooth edge. this corresponds to the ‘stuck on’ appearance of seborrhoeic keratoses. A melanoma will not have such a clean edge as this, as I will show when I post more examples.

The lines coming in from the left indicate milia like cysts (or star bright dots) which although they are seen in some other lesions are especially characteristic of seborrhoeic warts especially when multiple.  The lines coming in from the right indicate comedo like openings, or keratin pits. These are again very characteristic of seborrhoeic warts.

The area within the ellipse could deceive the beginner into diagnosing a blue grey veil, which is a melanoma feature. That’s a legitimate question, but this lesion has no features of a melanocytic lesion such as reticular network or globules and is packed with typical features of a seborrhoec keratosis, so we need not be concerned. Bluish areas like this are often seen in these harmless lesions, as the learner will discover after seeing a few hundred.

Dermoscopes are great for sorting the seborrhoeic wart from the melanomas. If in doubt, shave and lightly cauterise for histology or better still at the lower end of the learning curve, ask a more experienced diagnostician. Vast numbers of these harmless lesions are referred urgently as suspected melanomas, this does not only cost money but time and anxiety to the patient who is put on an urgent skin cancer pathway (there is some terrifying melanoma related material on the web). This cost and worry can often be avoided by adequately skilled dermoscopy at the first consultation or at least in the health centre within a few days. Always, if the dermoscopy student is in doubt, then refer-but take photos, make notes and check back.


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