Microcirculation in Psoriatic Skin

Abstract

Our previous electron microscopic studies on psoriatic skin demonstrated thin-walled vessels that resembled lymphatics but which contained erythrocytes and had prominent endothelial cell gaps. Gap formation was also found in venous capillaries and postcapillary venules. Reconstruction techniques and further studies with light and electron microscopy have now shown that the thin vessels are lymphatic. The best explanation for the abundance of erythrocytes in their channels is a clearing of the interstitium of red cells escaping from leaking capillaries and venules. Lymphatic capillaries are very numerous and dilated in the lesions and normal skin of psoriatic patients. They are rare and only minimally dilated in control specimens. The superficial lymphatic plexus begins as blind channels in the papillae that link up with one another to form a network in the papillary dermis. Valves are present at most points where lymphatic capillaries join one another. Lymphatic capillaries closed at both ends and unattached to the surrounding plexus are found in psoriatic skin and may be a lymphatic reserve. The blood vessel gaps develop at intercellular junctions and their profiles are identical to those produced by the local injection of histamine. However, distortion of the endothelial cell nuclear membrane which accompanies histamine-induced gaps in animals could not be found in psoriatic vessels, nor could it be produced in normal individuals injected intradermally with histamine. The blood vessel gaps were easily found in psoriatic skin and were very uncommon in control specimens. The gaps may represent an inherent weakness in psoriatic vessels or a histamine-type response to unidentified stimuli in psoriasis.