Ultrastructure of the capillary loops in the dermal papillae of psoriasis.

Electron microscopy was used to define the ultrastructure of the capillary loops in the dermal papillae of psoriatic lesions. Pustular psoriasis of von Zumbusch and psoriasis vulgaris were studied before and after treatment with the Goeckerman regimen. Capillary loops were reconstructed from 1-mum plastic-embedded sections. Ultrathin sections were taken at intervals for correlation with the 1-mum sections. There were no ultrastructural differences between the capillary loops in psoriasis vulgaris and pustular psoriasis. The intrapapillary portion of the loop was predominantly a venous capillary. Four basic ultrastructural loop patterns were recognized which can serve as markers in studying the responses of psoriatic loops in various experimental situations. Following 3 weeks of Goeckerman therapy, the morphology of psoriatic capillary loops changed from venous capillaries to arterial capillaries which are found in the papillae of normal skin. This transformation was observed to begin 48 to 72 hr after the initiation of therapy.