Multiple-band melanonychia striata.

KEY LEARNING POINTS MS is defined as a single or multiple black/brown pigmentation bands arranged lengthwise along the nail unit. Physiological MS is more commonly seen in darker phototype individuals and is quite unusual in fair-skinned ethnic groups. MS is the result of increased melanin production by nail matrix melanocytes, which produces a visible pigmentation band in the nail plate. Distinction should be made between melanocytic activation (increased melanin synthesis with a normal number of melanocytes) and melanocytic hyperplasia (increased melanin synthesis with an increased number of melanocytes). The latter condition includes melanoma, which is the most concerning (albeit infrequent) cause of melanonychia in children. Multiple-band MS (as in our patient) makes melanocytic naevus and melanoma less likely as a cause. Our patient’s persistently good clinical condition since the appearance of MS (3 years ago) allowed us to exclude the rare systemic causes of multiple-band MS (eg, Cushing syndrome, hyperthyroidism, malnutrition, vitamin B12 deficiency, scleroderma and systemic lupus erythematosus inter alia).