A prominent pigment network may be due to increased melanin in the epidermal ridges of the skin, such as found in Becker’s or pigmented epidermal naevi. This occurs in the absence of significant melanocytic proliferation or nesting.
A 28-year-old man presented with a large (9 x 16 cm) dark brown patch localised to his left inner upper arm and shoulder (Figure 1). The pigmentation had appeared at the time of puberty, and had remained static for a number of years. The patch had a reticulate and stippled pattern with an irregular border. Dermoscopy revealed a prominent and extensive pigment network that was uniformly coloured (Figure 2). Skin biopsy showed an epidermis that had a well developed rete ridge system which was deeply pigmented at its base, but the number of melanocytes appeared normal and there were no melanocytic nests (Figure 3).