What is the likely cause of the longitudinal melanonychia?
The longitudinal melanonychia most likely to represent malignancy is that arising as a solitary pigmented streak in a white person with fair colouring and of middle age or older. In a dark skinned person, benign nail pigmentation becomes increasingly common with age and is typically found in varying degrees of intensity on several digits. In all instances, there needs to be careful evaluation to determine the cause of the pigmentation [30,34]. If no satisfactory benign explanation can be found, then they should be reviewed by a Dermatologist to consider the need for biopsy. The most common causes are drugs, trauma, fungal infection (Figure 6) and inflammatory diseases such as lichen planus which may be manifest elsewhere on the skin. Both squamous cell carcinoma and melanoma would be considered during assessment. In rare instances, the pigment is exogenous, such as that produced by potassium permanganate. This can be demonstrated by scraping the surface of the nail. Where there is onyc
