Background: Ungual melanoma is the most serious disease affecting the nail. The majority start with a longitudinal brown streak in the nail.
Objective: To outline the different nail pigmentations, their differential diagnoses, treatment, and prognosis.
Method: Clinical and histologic evaluation of dark nail pigmentations.
Conclusion: Brown to black nail pigmentation may be due to different coloring substances of exogenous and endogenous origin. Exogenous pigmentations usually are not streaky or do not present as a stripe of even width with regular borders. Bacterial pigmentation, most commonly due to Pseudomonas aeruginosa or Proteus spp., have a greenish or grayish hue and the discoloration is often confined to the lateral edge of the nail. Subungual hematoma may result from a single heavy trauma or repeated microtrauma which often escapes notice. The latter is usually found on the medial aspect of the great toe. Although oval in shape, it commonly does not form a neat streak. Melanin pigmentation in the form of a longitudinal streak in the nail is due to a pigment-producing focus of melanocytes in the matrix. Neither the color intensity nor the age of the patient are proof of benignity or malignancy although subungual melanomas are very rare in children and malignant longitudinal melanonychia is usually wider than 5 mm. Hutchinson's melanotic whitlow, nail dystrophy, and a bleeding mass strongly suggest malignancy. Treatment is as conservative as possible in order to keep the tip of the digit; once the melanoma is completely removed, amputations have not been shown to prolong the disease-free survival time.