What is in your differential diagnosis for a thin brown line of parallel bands, regular in width that span nail fold to free nail edge?
A Long Brown Line Under the Fingernail of an African-American Girl. Your Dx?
Patient is a 14-year-old African-American female. Brown stripe running down the length of her index fingernail has been present for 4-5 y. Family members have same pigmentation, mostly under thumbs.
Note a brown, 1- to 2-mm wide longitudinal line. There is: no nail dystrophy, no variation in pigment, no involvement of periungual skin.
Differential diagnosis: Melanotic macule (melanonychia striata or longitudinal melanonychia) of the nail unit; nail matrix nevus; onychomycosis; subungual hematoma; subungual melanoma.
Answer: A. Longitudinal melanonychia.
More common in dark-skinned individuals; in Caucasians, warrants referral to a dermatologist.
Always refer if: Indistinct borders; greater than 3mm wide; changes in lesion or nail plate; involvement in one digit; extension of lesion into nail fold (Hutchinson’s sign); family history of melanoma.
What is longitudinal melanonychia? Result of increased production of melanin in nail matrix; when benign, pigment density is uniform; width varies, may increase over time; usually less than 3mm wide.
Causes:
Melanocytic activation--increased production, deposition of melanin into onychocytes, w/o increase in melanocytes.
Melanocytic hyperplasia--increased number of melanocytes are found within the nail matrix.This can represent either a benign or a malignant process.
Causes of melanocytic hyperplasia: Benign--lentigines; melanocytic nevi. Malignant--melanoma of nail bed. Also, bacterial pathogens can stain nail surface as can tobacco, potassium permanganate, silver nitrate, paint, dirt.
Diagnosis: Dermatoscopic examination of benign lesion will show parallel light to dark brown lines/bands regular in color, width; clearly defined borders; width 3mm or less.
Be concerned about malignancy if: present in a Caucasian; width greater than 3 mm; pigment variegation; Hutchinson's sign; nail dystrophy .
Patient counseling: common in dark-skinned people; no indication for a biopsy at this time; observation will continue; notify provider of any changes.
The vertical brown line under the index fingernail of a African-American teen girl has not been cause for alarm over the 4-5 years she has been a patient at this clinic. The teen's sports participation physical examination with a resident in the room offers a teaching opportunity this physician can't pass up. What does this line look like to you? Is it ominous or otherwise benign? What's in your differential -- and what's your diagnosis?
