Light and electron microscopy of psoriatic skin before and during retinoid (Ro 10-9359) and retinoid-PUVA treatment.

Eight patients with psoriasis (pustular, erythrodermic or severe plaque type) were treated successfully with retinoid (Ro 10-9359) or with retinoid followed by PUVA (RePUVA). The histological changes in recovering skin were examined during 14 weeks. Treatment resulted in normalization of keratinocyte differentiation with fine structural changes suggesting decreased metabolic activity and a reduction of mitoses. There was an increase in the number of keratohyalin granules and of tonofilaments and desmosomes and a decrease in leukocytes in the epidermis. The different cell organelles were studied in detail, but the exact mechanism of retinoid action remains unsolved. Although the treatments were clinically highly effective, total normalization of the histological and electron microscopical picture was not achieved.