Irregular dark ‘mole’ on back of hand

This large dark lesion on elderly, white, sun-damaged skin breaks the ABCD rule. It is Asymmetrical, has an irregular Border (Colour is 2 shades of brown, which is usually OK) and diameter well over 6mm. So, breaks 3 out of 4 ABCD rules. Could it be a melanoma?

dark lesion back of hand

On palpation, the lesion is flat (if you were just touching and couldn’t see it, you wouldn’t know it was there) and it was not rough or scaly.

Dermoscopy is decisive.

harmless solar lentigo

The dermoscopy shows a very homogenous light brown colour (trivial variations of the shade of brown do not matter) and pattern. The pattern is mostly featureless/structureless/no overall pattern, with evenly distributed small pale clods, which represent sweat gland openings.

Study the edge. Yes, it is very raggedy (some call this appearance moth eaten or scalloped) but it is very well defined all the way round. This is often called a lentigo like edge and is reassuring.

This is a solar lentigo, also called lentigo simplex. This lesion sometimes causes confusion, not least because of the word ‘lentigo’ which also occurs in the term lentigo maligna and lentigo maligna melanoma. This is unfortunate since solar lentigo and lentigo maligna are made up of completely different cell types and are not related. Solar lentigines (the correct plural name) are made up of deeply pigmented keratinocytes and they CAN NOT and DO NOT turn into lentigo maligna, which are made of melanocytes, a completely different kind of cell. True, they occur in the same locations and age groups, are both related to chronic sun exposure, and there may be some clinical overlap (which can usually be resolved by correct use of dermoscopy) but they are different kinds of thing and quite unrelated.

I will post a few more cases of both lesion types over the coming weeks to help explain this point. I see a lot of patients who are scared (as are their GPs) by these lesions, which can be large, dark and irregular. Dermoscopy almost always allows us to give confident and safe reassurance at the first consultation, saving worry and waste.

PS people often refer to solar lentigines as old age spots or sun spots. When talking to patients, I often refer to them as ‘flat brown marks’ which is accurate and meaningful, because as long as they stay flat (*) and no colour but brown, you usually need not worry. A lentigo maligna will generally develop black, grey or blue colours as it develops.

(*) You can develop seborrhoiec warts on top of these, they are harmless.