What is a lentigo maligna?
A lentigo maligna (on the face also called Hutchinson’s melanotic freckle) is a pigment spot regarded as a precursor of melanoma. It occurs mainly on heavily sun-exposed skin, particularly the face. In fact it is a variant of melanoma in situ.
Who gets a lentigo maligna?
Lentigo maligna occurs mainly in people from middle age onwards. The chance clearly increases with the years, and the proportion of over-75s among patients is large. Women seem to have a slightly greater chance than men.
How does it develop?
A lentigo maligna arises from an ordinary lentigo (sun spot), or in its early existence strongly resembles such a benign pigment spot. Past sun damage plays the most important role.
What does a lentigo maligna look like?
A lentigo maligna is distinguished from an ordinary lentigo by variable and irregular pigmentation. The border with the normal skin is often unclear in places, and a pigment spot that keeps growing should be viewed with suspicion. Some lentigo maligna spots are very clearly variably and darkly pigmented, but some are not even very striking in colour and are largely light brown.
How is the diagnosis made?
When a lentigo maligna is suspected (after clinical and dermatoscope assessment), the dermatologist will in principle remove it surgically. The problem is that most lentigo maligna spots arise on the face and are sometimes already quite large (several centimetres) when first noticed, so a biopsy is often taken first for the pathologist. Unfortunately the pathologist does not always give a definitive diagnosis on the biopsy and may ask for the whole spot to be removed to establish it — but fully removing a large facial lesion in a cosmetically acceptable way is often difficult.
How is a lentigo maligna treated?
- Excision — the best treatment, since it could ultimately turn into melanoma. A lentigo maligna should in principle be removed with a 5 mm margin of healthy skin, though the borders are often hard to establish exactly, and even with the usual margins microscopic examination sometimes shows it was not completely removed. Full removal is often not possible in an acceptable way near important structures such as the eyes, nose or mouth.
- Nitrogen (cryotherapy) — because it is a melanoma precursor, the nitrogen must be applied fairly intensively, giving a high risk of scars; it is too imprecise and certainly not first choice.
- Radiotherapy — in principle a good option, though the chance of recurrence is fairly large and it cannot be repeated for a recurrence.
- Imiquimod cream — applied daily for about 12 weeks, causing an inflammatory reaction; there is still a considerable chance of recurrence afterwards.
Follow-up: after any treatment, close follow-up in the following years is always warranted, because the chance of recurrence is considerable with all options.
When to see a doctor
See a doctor for any pigment spot on sun-exposed skin (especially the face) that is unevenly coloured, irregular, growing or has an unclear border, so a lentigo maligna can be assessed and treated.