Dark Lines on Toenails

Dark lines on the toenails are often seen in the office and asked about by patients.  Although most presentations of melanin deposition in nail plate tissue represent a benign melanocytic process in the nail matrix, a small percentage may represent melanoma, a potentially fatal cancer. Pigmentary changes in nail appearance may occur from trauma, inflammatory disease, occupational exposure and fungal infections among others.

The deposition of melanin in the nail plate is called longitudinal melanonychia.  A short list of potential causes include:

• nevi in the nail matrix, characterized by an increased number of melanocytes arranged in nests;
• matrix melanotic macule, which one would histologically see as an increase in the amount of melanin with or without hyperplasia;
• non-melanocytic nail tumors, such as squamous cell carcinoma;
• human immunodeficiency virus (HIV) infection;
• inflammatory nail disorders;
• trauma;
• pregnancy;
• medications;
• endocrine disorders, such as Addison’s disease and Cushing’s disease; and/or
• melanoma.

Acral melanoma tumors exhibit aggressive histopathologic features associated with a poorer survival outcome.  It is the most common type of melanoma in deeply pigmented individuals, and is mostly diagnosed between the ages of 40 and 70.  This can be confused with ethnic or racial pigmentation, which in darker-skinned individuals, longitudinal melanonychia can commonly occur in one or multiple nails, and is mostly benign.

According to Baran and Dauber, suspicion of melanoma includes the following:

1. begins in a single digit of a person during the sixth decade of life or later;
2. develops suddenly in a previously normal nail plate;
3. changes, including darkening or widening (especially at proximal end);
4. occurs in either the thumb, index finger, or big toe;
5. occurs attendant to a history of digital trauma;
6. occurs as a single band in the digit of a dark-skinned individual, especially if it is in the thumb or big toe;
7. appears with blurred as opposed to sharp lateral borders;
8. occurs in a patient with a prior history of melanoma;
9. occurs in a patient identified as having increased risk for developing melanoma, such as a patient with family history of melanoma or dysplastic nevus syndrome;
10. occurs with nail dystrophy, destruction or partial nail plate absence.

According to Levit and colleagues, suspicion of melanoma includes the following:

• A. Age: Range 20 to 90 years, peak fifth to seventh decade, African-American, Native American and Asian races.
• B. Band. Pigment is brown-black. Breadth is greater than or equal to three mm. Border is irregular or blurred.
• C. Change. Rapid increase in size or growth rate of band. This can also refer to a lack of change, namely failure of nail dystrophy to improve with treatment.
• D. Digit involved. The thumb is the most common digit involved followed by the big toe and index finger. A single digit is more worrisome than multiple digits. Dominant hand involvement is more common than that of a non-dominant hand.
• E. Extension. Extension of pigment on to the proximal or lateral nail fold (Hutchinson’s sign) or the free edge of the nail plate.
• F. Family or personal history. Previous history of melanoma or dysplastic nevus syndrome.

If you suspect that you have melanona according to either of the criteria above, please contact Dr. John Hoy at Seattle Foot and Ankle Center in Seattle, Washington, to discuss a biopsy procedure to rule out cancer.