Melanonychia as a diagnostic challenge

Abstract

Melanonychia involves black-brown discoloration of the nail plate and nail matrix epithelium caused by melanin accumulation. Etiologically, we distinguish simple melanocyte activation and melanocyte proliferation. Melanocyte proliferation can be benign (such as lentigo and nevus) and malignant (subungual melanoma). Although they have similar clinical characteristics, their prognoses are significantly different. The paper presents two cases of melanonychia. In the first case, a 13-year-old boy had linear black-brown discoloration of the nail plate of the index finger of the left, non-dominant hand. There was no nail plate dystrophy, periungual pigmentation, or bleeding. Medical and family histories were unremarkable. Onychoscopic examination diagnosed a nevus of the nail plate. In the second case, an adult woman had linear brown discoloration of the nail plate of the thumb of the right, dominant hand. The discoloration had discreetly irregular edges without signs of nail plate dystrophy, periungual pigmentation, or bleeding. Medical and family histories were unremarkable. After onychoscopic examination, longitudinal excisional biopsy was indicated, establishing the diagnosis of lentigo. Careful history taking, physical examination, onychoscopic examination, and ultimately biopsy with histological examination allow for determining etiology, as well as for an early diagnosis of subungual melanoma as the most important precondition for successful disease treatment.