A 52-year-old woman presented with black discoloration of the fingernails (Figure 1). She had no trauma to the area and no associated pain, rash, swelling, or drainage. She had no other symptoms, including shortness of breath, chest pain, or visual disturbances. Her medical history was significant for type 2 diabetes mellitus, hypertension, thrombocytosis, and coronary artery bypass. The patient was taking metformin, glipizide, lisinopril, hydroxyurea, and topiramate.

Her vital signs were normal on physical examination. All fingernails showed black discoloration but no pitting, spooning, or ulceration. The fingertips were warm to the touch and nontender to palpation.

Question

Based on the patient’s history and physical examination findings, which one of the following is the most likely diagnosis?

• A. Mees lines.

• B. Melanonychia.

• C. Onychomycosis.

• D. Subungual hematoma.

• E. Subungual melanoma.

Discussion

The answer is B: melanonychia. Several medications are known to induce black discoloration of fingernails, including antimalarials, chemotherapeutics (hydroxyurea, cyclophosphamide, fluorouracil), phenytoin, and tetracyclines.¹ The discoloration may present as a longitudinal, transverse, or diffuse band pattern. Patients may have coexisting diffuse pigmentation of the skin (melanoderma). Melanonychia can also occur with nutritional deficiencies (folate, vitamin B₁₂), connective tissue diseases (systemic lupus erythematosus, scleroderma), endocrinopathies (Addison disease, Cushing syndrome, hyperthyroidism), or physiologic processes (pregnancy).¹