Some drugs may cause dark pigmentation of finger or toe nails by stimulating melanocytes in the nail bed to produce melanin.
Patterns:
(1) longitudinal
(2) transverse (seen typically with a course of chemotherapy)
(3) diffuse
Usually several nails are involved.
Drugs associated with melanonychia:
(1) chemotherapeutic agents (cyclophosphamide, doxorubicin, fluorouracil, bleomycin, hydroxycarbamide/hydroxyurea)
(2) zidovudine
(3) psoralens
(4) radiation therapy
Risk factors:
(1) dark skinned individual
(2) multiple agents
(3) high doses of causative agents
(4) past history of melanonychia to the drug
The diagnosis can be confirmed by demonstration of melanin in nail clippings with the Masson-Fontana stain.
