Blood flow in psoriatic plaques before and after selective treatment of the superficial capillaries

Blood flow is substantially raised in psoriatic plaques. In addition, mechanisms of vasoconstriction and vasodilatation (locally and neurally mediated), although intact, are altered in magnitude. The elevated blood flow is considered to be a result of abnormalities (increase in vessel number, width and length) in the superficial capillary loops rather than changes in the deeper feeding vessels (arterioles).

To determine if selective thermolysis of psoriatic capillaries with a pulsed dye laser (PDL) leads to normalization of blood flow and also if the vasoconstrictor and vasodilator responses are returned to normal magnitude.

Laser Doppler red cell flux was recorded from plaques on the forearm or elbow (untreated plaque site) and from clinically uninvolved skin at an equivalent site on the opposite limb. Plaques were treated on three occasions, at 2-weekly intervals, with a PDL. Laser Doppler red cell flux measurements were then repeated, 2 weeks after the final laser treatment was performed (treated plaque site).

There was significant clinical improvement in plaques after treatment (P = 0.02), but complete clearance of lesions did not occur. Blood flow in plaques under basal conditions remained significantly elevated above blood flow in clinically uninvolved skin, despite laser treatment (P < 0.001). The physiological tests of resistance vessel function showed that the laser did not impair the ability of psoriatic resistance vessels to constrict and dilate. However, there was only partial resolution of the percentage responses to the provocation tests towards the values recorded in clinically uninvolved skin.

The results indicate that it is unlikely that the reduced resistance of the expanded superficial capillary bed is solely responsible for the massively elevated blood flow in plaque skin. It is more likely that the vascular abnormalities in psoriasis also extend to involve the deeper, larger resistance vessels (arterioles).