[Pigmented lesions of the nail apparatus].

Linear pigmentation of the nail apparatus most reflects longitudinal melanonychia. It results either from simple activation of matrical melanocytes induced by various factors or from benign (lentigo or naevus) or malignant (melanoma) melanocyte hyperplasia. Hematomas and some fungal infections can falsely resemble linear pigmentation. Non-linear pigmented lesions of the nail bed are most often subungual hematoma or infections (fungal, or pyocyanic superfection of a loosened or separated nail). Opening the nail bed directs the diagnosis. A possible tumoral cause should be kept in mind, especially melanoma, or carcinoma.