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

Abstract

Background: 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).

Methods: 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.

Results: 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.

Conclusions: 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.