Chapter 18: Benign Melanocytic Lesions of the Nail

SUMMARY

• Longitudinal melanonychia (LM) is defined as a longitudinal band of brown-black pigment that runs from the nail matrix to the distal nail plate.

• It is important to distinguish benign etiologies of LM, like benign melanocytic activation, lentigos and nevi, from nail melanoma.

• A thorough history, physical exam, and onychoscopic inspection can provide helpful clues and guide management; however, excision and histopathological analysis remains the gold standard for diagnosis.

TIPS FOR DIAGNOSIS

• The ABCDEF criteria can help estimate a lesion’s benign nature and guide management.

• LM in a child is unlikely to be malignant, despite other clinical features.

• LM that is ≤ 3 mm wide, homogenous in color, and regular in line width and distribution is more likely to be benign.

TIPS FOR TREATMENT

• Lesions that are likely benign based on history, physical exam, and onychoscopy may be followed up clinically without biopsy.

• Whenever there is doubt of whether or not a lesion is benign or a lesion evolves, excise.

DON’T FORGET

• Lesions affecting multiple digits are more likely to be benign compared to solitary lesions.

• Any change or lack of resolution of a previously diagnosed benign lesion is reason for re-evaluation.

PITFALLS AND CAUTIONS

• While benign LM is extremely common in individuals with darker phototypes, nail melanoma is still possible in these patients.

• As solitary lesions in children are likely to be benign, biopsy is typically not necessary and should be avoided.

• While history, physical exam, and onychoscopy provide helpful clues to guide management, histopathological analysis is the only way to prove a lesion’s etiology.

EXPERT PEARLS

Onychoscopic evaluation:

• LM that is a gray homogenous band with a gray background is likely the result of benign melanocytic activation.

• LM with a brown background, regular width and spacing of lines, and homogenous pigment distribution is likely the result of benign melanocytic proliferation (lentigos and nevi).

• LM with a brown background, lines of variable width and spacing, and heterogenous pigment distribution is concerning for malignancy in adults.

PATIENT EDUCATION POINTS

• Minimize chronic trauma to the nails by avoiding tight shoes, high heels, and prolonged standing.

• Educate patients on how to monitor for evolution or change of the lesion (growth, change in color, lack of resolution, etc.).