Pigmentary mosaicism of hyperpigmented type in two sisters.

A 17-year-old girl and her 15-year-old sister presented with progressively increasing streaks of reticulate hyperpigmented macules arranged in a whorled pattern over the trunk and extremities (Figure), which appeared soon after birth. The face, palms, soles, eyes, and mucous membranes were spared. Both parents were unrelated Saudis. There was no history of any preceding eruption or any associated systemic abnormality, except for recurrent oral ulcers in both patients for several years. The younger one also had one episode of genital ulcers. Dermatological examination of both parents and the patients' three brothers and one sister were normal with no history of oral ulceration. Examination revealed few aphthous ulcers in either cases, but no joint or eye symptoms. Pathergy testing in both cases was negative. Ophthalmological examination and consultation revealed no signs of Behcet's disease. Routine blood tests did not show any abnormalities. Skin biopsies were taken from pigmented and normal skin in both patients. Histopathological examination of pigmented skin in both cases revealed basal cell hyperpigmentation with pigmentary incontinence. Similar features but in milder form were seen in the biopsies of normal skin in both cases.