An in vivo study of the microlymphatics in psoriasis using fluorescence microlymphography.

Angiogenesis is a recognized event in psoriasis. Previous ultrastructural studies have demonstrated lymphatic capillaries extending high into the dermal papillae. Using the novel method of fluorescence microlymphography which permits visualization of upper dermal initial lymphatics in vivo we tested the hypothesis that lymphangiogenesis exists within plaque psoriasis. Six patients underwent fluorescence microlymphography with fluorescein isothiocyanate-dextran administered intracutaneously within a psoriatic plaque on the leg. Stereological analysis permitted quantification of the lymphatic network opacified both within (lesional) and without (perilesional) the plaque. Results showed a greater spread of tracer from the depot into perilesional skin than into the plaque (P < 0.006). The mean length of lymphatics per unit area at increasing distance from the centre of the depot was also increased for the perilesional skin, 10.5 +/- 1.9/cm2 (mean +/- SEM), compared with lesional skin, 3.06 +/- 0.8/cm (P < 0.001). The cumulative lymphatic length was also greater in perilesional, 22 +/- 7.3 cm2, compared with lesional skin, 3.6 +/- 0.3 cm (P < 0.006). Fluorescence microlymphography has proved to be an effective in vivo technique for the assessment of the dermal microlymphatics in psoriasis. Stereology provided quantitative analysis of the lymphatic network visualized. Overall, there is a greater network of lymphatics in perilesional compared with lesional skin in patients with plaque psoriasis. This finding is at odds with the accepted view that the lymphatic dermal vessels are increased within the psoriatic plaque.