A 50-year-old African-American man is referred to dermatology by his primary care provider for evaluation of colored stripes in most of his fingernails. These have been present, without change, for most of his adult life.
The patient has been told these changes probably represent fungal infection, but being dubious of that diagnosis, he declined recommended treatment. Nonetheless, he is interested in knowing exactly what is happening to his nails.
He denies personal or family history of skin cancer and of excessive sun exposure. He reports that several maternal family members have similar nail changes.
Seven of the patient’s 10 fingernails demonstrate linear brown streaks that uniformly average 1.5 to 2 mm in width. The streaks run the length of the nail, with no involvement of the adjacent cuticle. Some are darker than others.
The patient has type V skin with no evidence of excessive sun damage.
What’s the diagnosis?