Pigmented skin lesions in tyrosinase-positive oculocutaneous albinos: a study in black South Africans

The aim of this study was to document the nature, prevalence, and distribution of pigmented skin lesions in tyrosinase-positive oculocutaneous albinism (ty-pos OCA), the most common recessive disorder in South Africa (overall prevalence, 1 in 3900).

Sixty-one black subjects with ty-pos OCA (mean age, 23 years) and 65 normally pigmented black control subjects (mean age, 29 years) were studied.

Pigmented skin lesions not directly related to sun exposure included nevi and pigmented macules on the palms and soles. Melanocytic nevi, mostly on the trunk, were present in 82% of subjects with ty-pos OCA and in 71% of controls. The mean numbers were, however, greater in the ty-pos OCA subjects than in the controls (12 and 7, respectively), being closer to those reported in whites. Palmoplantar pigmentation was present in 75% of the control subjects, but in none of those with ty-pos OCA. The most striking sun-related lesions were dendritic freckles, which were present in 43% of ty-pos OCA subjects, and were characterized by an irregular branched shape, light to dark brown color, and large size (0.5-3.0 cm). Clinically, they resembled solar lentigines, but histologically the rete ridges were often flattened and there was no increase in the number of melanocytes. Solar keratoses occurred less frequently in ty-pos OCA subjects with dendritic freckles (50% vs. 73%), which confirmed the sun-protective role of the increased ability to form pigment.

There were two major conclusions. Firstly pigmented nevi occur much more commonly in ty-pos OCA subjects than was previously thought, being similar in number to those found in white subjects. Secondly, dendritic freckles appear to represent a unique clinical and histologic entity found only on sun-exposed areas in ty-pos OCA subjects.