[Histopathology and histochemistry of psoriasis under photochemotherapy (author's transl)].

Fifty-two biopsies from involved and clinically normal looking skin of patients with psoriasis vulgaris and from normal control subjects, all being treated with 8-MOP-UVA (PUVA) were obtained between days 2 and 300. The following parameters were investigated: 1. initial PUVA effects; 2. initial regression of psoriasis under PUVA-therapy; 3. late effects of PUVA-therapy on regression of psoriatic lesions; 4. EFFects on melanocytes and pigmentation; and 5. long-term effects of PUVA-therapy. Paraffin embedded and cryostat sections were prepared with routine stains for light microscopy and enzyme histochemical special stains. The regression of psoriatic lesions following PUVA-therapy was separately assessed for epidermal and dermal components. The sequence of events was as follows: re-establishment of a continous stratum granulosum, re-establishment of a continuous normal appearing stratum corneum, regression of acanthosis and papillomatosis, and regression of inflammatory infiltration. During the initial phase of PUVA-therapy there is a sharp increase of melanocytes which leads to a foamy appearance of the basal cell area. Long term studies did not reveal actinic damage of the skin, neither in the epidermis (absence of actinic keratoses or squamous cell carcinomas) nor in the dermis (absence of actinic "solar" elastosis).