A woman presents with a 10-year history of asymptomatic mottled pigmentation localised to her axillae and groins. What is the cause?
A 34-year-old woman gave a 10-year history of asymptomatic mottled pigmentation localised to both her axillae (Figure 1) and groins. The pigmentation had a papular element and was persistent. Her mother and sister were similarly affected. Skin biopsy from the axillae showed an epidermis with an antler-like epidermal rete ridge system, which was hyperpigmented and projected into the superficial dermis (Figure 2). The melanocytes were present in normal numbers and there were no junctional nests.