Clinical and histopathological characteristics of pityriasis alba.

BACKGROUND: Pityriasis alba (PA) is a skin disorder characterized by asymptomatic, variably hypopigmented, slightly scaling patches with indistinct margins. It is sometimes difficult to clinically differentiate PA from other hypopigmented disorders such as naevus depigmentosus.

AIM: To examine the clinical and histopathological characteristics of PA that are important in differentiating PA from other hypopigmenting disorders.

METHODS: A clinical survey was carried out on 56 patients with PA. Histopathological features were investigated with immunostains for NKI/beteb antibody, melanoma antigen recognized by T cells (MART)-1 and S-100 protein, and by haematoxylin and eosin and Fontana-Masson stains.

RESULTS: Of the 56 PA patients, 10 (18%) had a previous history of atopic dermatitis and 9 (16%) had a solitary lesion. Histopathological study revealed markedly reduced pigment in the epidermis of lesional skin, but no significant difference in melanocyte count was found between lesional and normal skin. Ultrastructurally, degenerative changes in melanocytes and a reduced number of melanosomes within keratinocytes were seen.

CONCLUSION: No significant difference in the number of melanocytes between lesional and normal skin was seen. These findings should be considered when diagnosing and differentiating PA from other hypopigmentary disorders.