This woman’s linear hyperpigmentation is formally known as longitudinal melanonychia.
After the initial diagnosis, it is important to determine if the melanonychia is due to melanoma or a benign process. Many people with darker skin types (Fitzpatrick skin types V or VI) have several of these lines, so it is reassuring when these lines are present on multiple digits. Additional evaluation is warranted, however, when only 1 longitudinal melanonychia is present.
In this case, it was clear that the pigmentation was homogeneous and in a parallel line format. (Dermoscopy can aid in the evaluation of such lesions.) There was no spreading of the pigmentation onto the skin around the nail (Hutchinson sign), which would be suggestive of melanoma. The patient noted that the lesion had been present (without progression) over a 10-year period, which also was consistent with a benign process. A new lesion, rapid change, a triangular pattern wider at the cuticle vs the distal nail, and nail disruption are worrisome features that would have warranted a biopsy.
If a biopsy is called for, be sure to sample the origin of the pigmentation under the cuticle and the nail at the nail matrix. This requires partial or complete nail removal to reach the matrix, and there is a risk of permanent nail disruption. In light of this, it’s important to discriminate which lesions are at higher risk for melanoma.
In this patient, who had a stable lesion and no concerning history or findings, it was likely that she had a benign nevus or lentigo in the nail matrix. She was instructed to watch for any changes and to notify her physician if any occurred, as such changes might require a biopsy.
Photo and text courtesy of Daniel Stulberg, MD, FAAFP, Department of Family and Community Medicine, University of New Mexico School of Medicine, Albuquerque.