The effect of phototherapy on extracellular water and transvascular protein exchange in psoriasis

Seven patients with stable psoriasis vulgaris were treated with phototherapy (Goeckerman or PUVA) for 3 to 4 weeks. By combining the suction blister technique with studies on labelled albumin and inulin, the intra- and extravascular fluid volumes, the leakage of albumin from the total and the skin microvasculature, and the intra- and extravascular masses of albumin were measured before and after therapy. In accordance with previous studies, a shift of fluid from the intra- to the extravascular spaces, an increased leakiness of the involved skin microvasculature, and a lowered total mass of body albumin were found before therapy. Treatment induced a minor increase of the extracellular fluid volume [mean, 6.20 +/- 1.16 l/m2 (SD) v. 6.73 +/- 0.95 l/m2 (SD), P less than 0.1], a reduced vascular leakage of albumin from the involved skin vessels, and a significant increase of the total mass of albumin [mean, 124 +/- 20 g/m2 (SD) v. 139 +/- 30 g/m2 (SD), P less than 0.05]. The other measured variables did not change significantly. It is suggested that the observed change in extracellular fluid volume was mainly due to a treatment-induced decrease of the transepidermal water loss and/or a subclinical oedema of the skin, whereas the increase in total albumin mass was due to a reduction of the catabolism of the endogenous albumin caused by the decrease in the microvascular leakiness of the involved skin vessels.