Nail melanoma signs: dark streaks, nail changes and when to see a GP

Melanoma starts in pigment-producing cells (melanocytes), and these cells are found in the nail matrix under the cuticle as well as in the skin. The NHS says melanomas can appear anywhere on the body, and that rarer types can affect the eyes, soles of the feet, palms of the hands or genitals. The British Association of Dermatologists adds that they often appear on the hands, feet or nails, which are places where melanoma is less common in people with less pigmented skin, so the risk is not confined to those who burn easily or have fair skin.

Because nail melanoma can look like something harmless, it is often recognised late. A review of melanonychia notes an average delay in diagnosis of 2 years because nail apparatus melanoma is commonly misdiagnosed, which is the reason that a new or changing pigment change should be checked rather than watched indefinitely.

No single feature proves melanoma, but certain patterns are more concerning. The review describes melanonychia as brown or black hyperpigmentation of the nail, usually as a lengthwise band, and sets out an ABCDEF checklist for assessing a band.

• A brown or black band in a nail that is new, or a band that changes, for example by widening, darkening or becoming irregular (the review's "B" and "C").

• Age and background (A) and the digit involved (D), because a single nail is more concerning than several nails with similar bands.

• Extension of pigment onto the skin of the nail fold, called Hutchinson's sign (E), which the review calls an important but not absolute sign.

• A family history of melanoma (F).

• The NHS adds more general melanoma warnings: a mole or mark that changes in size, shape or colour, is painful or itchy, is inflamed, bleeding or crusty, or a new or unusual mark on the skin that has not gone away after a few weeks.

The NHS specifically says that a dark area under a nail caused by an injury is a different matter from one that has no such cause. The review points out that the causes of melanonychia range from common benign causes to melanoma and include both local and systemic disease, and that it can follow some medicines or fungal infection. In the case it describes, a pigmented fingernail band that had been hidden under nail polish turned out to be a fungal infection (onychomycosis) and resolved with antifungal treatment.

Whether an injury explains the mark is one of the first questions a clinician will ask, which is why the NHS draws the distinction.

The NHS says you will be asked about your health, family medical history and symptoms, including whether you or a family member have had skin cancer. The GP will look at the area and may ask whether they can photograph it to send to a dermatologist, which is called teledermatology. You may get an urgent referral for more tests or to see a specialist in hospital if the GP thinks you have symptoms that could be cancer, which does not definitely mean you have cancer.

The NHS stresses that finding a melanoma as early as possible can mean it is easier to treat.

The NHS says a dermatologist will check your skin, ask about changes you have noticed and may use a magnifying device to look at the skin more closely. They may cut out the mole and a small area of surrounding skin for laboratory examination, which is called an excision biopsy. The results should take about 2 weeks, although sometimes longer.

For a nail, the review says the biopsy site is chosen according to where the pigment originates, and techniques include punch biopsy, matrix shave biopsy and lateral longitudinal excision of the nail matrix. If melanoma is found, the NHS says you will usually need more tests such as a CT or MRI scan, tests to see whether the melanoma has spread to the lymph nodes and blood tests, to establish the stage.

The review says that treatment of melanonychia depends on the underlying pathology: treating a systemic disease, removing an offending drug or using antifungals may cause pigmentation to regress, and in most benign cases no treatment is needed. For subungual melanoma, depending on thickness and invasive characteristics, options include wide local excision, amputation of part of the digit and sentinel lymph node biopsy.

The NHS says a group of specialists will look after you through diagnosis, treatment and after, with a clinical nurse specialist as the main contact. The NHS emphasises that finding a melanoma as early as possible can mean it is easier to treat, which is why a changing nail is worth having looked at.