Questionable mole on back fails ABCD rule
The ABCD rule (Asymmetry, Border, Colour, Diameter) is a useful rule of thumb for picking out suspicious skin lesions, but it will give you a lot of false positives, i.e. harmless skin lesions that on this box ticking exercise will be thought malignant. A great many of these false positives will be seborrhoeic keratoses, and I am devoting the next dozen or so posts to these common lesions, which in their varied presentations so often catch us out.
This was a fairly large lesion on someone’s back. It was the biggest and oddest ‘mole’, so the ‘ugly duckling’ and also fails ABCD–Asymmetrical, irregular Border, diverse Colour and well over 6mm Diameter (in fact more like 2cm).
Sounds worrying-on paper. So guess what we do next?
Its a big lesion, so not possible to view it all in one go through the dermoscope. This was a representative sample including the border. It is warty-lots of little fingertip like projections (papillae= little fingers. Papillomatous is another word for warty). We can see fissures, some keratin and lots of tiny vessels in pale halos. Note that the vessels are very homogenous. Top dermoscopy researcher and teacher Professor Iris Zalaudek (check out her YouTube dermoscopy videos) says of vessels in dermoscopy…
A) evaluate their morphology (i.e. structure)
B) evaluate their distribution, and
C) look at non-vessel features of the lesion for clues.
I find this a useful approach. The vessels here are short loops and squiggles, they are very homogenous (i.e. they all look very much the same as each other) and their distribution is very regular all through the lesion. This is one of the typical appearances of seborrhoeic keratosis.
The fact of part of the lesion being darker means nothing-seb ks vary in colour quite a bit, we have already made a positive diagnosis of a seb k so varied colour can be discounted. The dark may represent thrombosed vessels due to minor trauma.
There are no features pointing to a skin cancer. The patient can be safely reassured.