Nail melanoma is the main reason that you are asked to remove your socks at a full skin check.
What are the clinical features?
What are the signs of a nail melanoma?
The slightly pale curved area found at the base of the nail (like a quarter moon) is called the lanula and melanomas are situated under the lanula. You won’t actually see the melanoma under the lanula. Instead, the melanoma is seen as as pigmented brown / black parallel lines along the length of the nail from the base towards the tip.
The pigmentation may cause the nail to split or bleed. It can be quite painful as the nail can separate from the nail bed and cause the whole nail to deteriorate.
There’s a fairly long list of possible causes of longitudinal nail pigmentation (longitudinal melanonychia):
- Ethnic hyperpigmentation
- Malignant Melanoma (of the nail matrix)
- A benign mole (nevus)
- drug induced (eg. amiodarone, tetracycline)
- inflammatory causes
- fungal nail infection
- Rare causes eg. Addison’s disease, radiotherapy
The most common causes are benign moles, trauma and ethnicity.
How is it diagnosed?
A dermatoscopic examination will help determine the diagnosis of nail melanoma. A gel is used to interface between the dermatoscope and the nail.
The dermoscope is switched onto the non polarized light setting and the nail is then examined.
Under a dermoscope, the colour of the pigment can be much better distinguished than with the naked eye.
In simple terms, melanomas or moles are brown or black whereas the other causes are more likely to be grey in colour. Dermoscopy may show the lines as being made up of several different colours and separated by varying distances. The lines of a benign nail mole are usually of the same colour and the lines a similar distance apart. Hutchinson’s sign may also be revealed only with dermoscopy.
It can be very difficult, even with dermoscopy, to exclude melanoma from a traumatised nail. In these situations, the trauma creates brown lines on the nail (both from bleeding and inflammation that occurs during the healing process) and may look concerning enough to indicate the need for a biopsy.
What is the treatment?
Nail melanoma is treated surgically. The entire nail needs to be removed and then the growth.