Based on the distribution, color, location, and chronic nature of the lesion, we were concerned that our patient might have a melanoma.

But the biopsy showed something quite different: black cotton debris that was stuck under the nail. The final diagnosis: sock debris.

This case is a prime example of why we generally start with the least-invasive procedure for diagnosis. By performing a biopsy of just the nail, instead of the underlying skin, as well, we were able to save this patient from unnecessary injury.

But when the clinical signs point more clearly to a melanoma, it may be necessary to go directly to a more invasive test.

It is important to pay attention to changes in your fingernails and toenails.

If you notice a new discoloration under a nail, but cannot recall any kind of trauma that might have caused bruising, it is best to see your dermatologist as soon as possible. If you do have melanoma, early diagnosis is crucial for effective treatment.

Nails can reveal information about your overall health. If any changes occur, such as longitudinal or latitudinal lines, discolorations, and/or pitting (small depressions in the nail), tell your doctor. Tests may be needed to find the cause.

- Joya Sahu and Robert Duffy