Reticulated black solar lentigo ('ink spot' lentigo)

Pigmented lesions that are black and have an irregular outline are often considered suspicious for melanoma; however, these features may be seen in benign lesions. The reticulated black solar lentigo is such a lesion and is described in a clinicopathologic study of nine lesions in eight patients.

The "ink spot" lentigo is distinguished clinically by its color and wiry or beaded, markedly irregular outline. It has a reticulated pattern and most resembles a spot of ink on the skin. In this series of patients, the lesions were limited to sun-exposed areas of the body and had a distribution pattern similar to that of solar lentigines. Although all the patients were of Celtic ancestry and had numerous solar lentigines, they usually had only one black lentigo (range, one to four; mean, 1.6; median, one). Histologic evaluation, including electron microscopy and dopa-incubated vertical sections, demonstrated lentiginous hyperplasia of the epidermis, marked hyperpigmentation of the basal layer with "skip" areas that involved the rete ridges, and a minimal increase in the number of melanocytes.

Because of their dark color, irregular border, and limited number, reticulated black solar lentigines were of concern to patients and primary care physicians. However, the characteristic features of these lesions allow one to make the clinical diagnosis of a benign lentigo.