PITYRIASIS ALBA - A HISTOLOGIC-STUDY

Background. Pityriasis alba is a common dermatitis, but only a few his tologic studies have been reported and most of these maintain that its microscopic features are those of a chronic nonspecific dermatitis. M ethods. A retrospective light microscopic study was performed on biops y specimens taken from 39 patients with localized pityriasis alba on f ace, arms and forearms without signs of atopy. Thirty-two patients wer e girls or women and seven were boys or men, with ages ranging from 7 to 37 years. The duration of illness varied from 1 month to 10 years. The clinical picture was characterized by three clinical stages: papul ar erythematous, papular hypochromic, and smooth hypochromic. Results. The histologic study revealed features that were suggestive, though n ot pathognomonic, of the diagnosis. The most remarkable changes involv ed the pilary apparatus, which showed horny plugs, spongiotic edema, a nd atrophic sebaceous glands. There was also a disturbance of melaniza tion secondary to epithelial damage. The tissue reaction was more cons picuous in the skin lesions with follicular papules. Conclusions. A hi stopathologic diagnosis of pityriasis alba may be proposed when the fo llowing features are seen in a biopsy specimen taken from a skin lesio n with follicular papules: (1) irregular pigmentation by melanin of th e basal layer; (2) follicular plugging; (3) follicular spongiosis; and (4) atrophic sebaceous glands.