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December 6, 2017 / molehunter

Dark mark under fingernail

Working in a skin cancer screening clinic, I see a lot of worried people. I am so glad to be able to reassure the majority that they don’t have a skin cancer. At least once a month I see someone with a dark mark underneath a fingernail or toenail.

Melanoma can affect the fingers and toes, but usually pigmentation under the nail is due to blood, regardless of whether the person remembers trauma. The most minimal knock can cause a microscopic droplet of blood to leak under the nail and spread out like a drop of ink between two microscope slides.

Here is a case which presented in a person of darker skin.

nail (2)

This plain view looks a bit worrying as the pigmentation appears black and is continuous with the proximal nail fold, also it’s wider at the base (which is what melanomas can look like) and there appears to be some pigment in the surrounding skin. However, this is a dark skinned person, so pigment change is less sinister, often due to inflammation. Lets look through a dermoscope.

nail (1)

I am immediately reassured, as this looks like blood, not melanin. a decision was made to photograph and review.

This is that the nail looked like 8 weeks later.

nail 3 and 4 (1)

And here is the dermoscopy.

nail 3 and 4 (2)

The pigment has almost all gone, and what we can see is just small linear streaks of blood. There is some ridging in the nail, most likely all due to some forgotten trauma. The patient was spared a painful nail bed biopsy.

I will post a few more images of nails in due course. I don’t have any images of melanoma affecting fingers and toes, they are not common, I have only seen a couple that I remember and was unable to photograph them. For every nail bed melanoma I have seen, I see at least 30 cases of blood under the nail. Dermoscopy is of great value in confirming this diagnosis, if you know what to look for.

For medical learners (for whom this blog is mainly intended although it’s open to the general public) there are some very good pictures of nail melanoma to be found on line. Eric Ehrsam’s blog is good (click on  the link) and YouTube videos by Professor Luc Thomas of Lyon, France. Luc is the acknowledged top expert on dermoscopy of the nail unit and his videos are excellent, here’s a link to one of them (warning, includes images of a nail bed biopsy, not a very nice procedure although sometimes necessary).





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