Psoriasis treated with dithranol: a pilot study on in vivo reflectance confocal microscopy.

Background: There are only limited histomorphological data on the response of psoriatic skin lesions to topical dithranol. In vivo reflectance confocal microscopy (RCM) in psoriatic skin is highly correlated with histopathological findings and allows non-invasive monitoring of treatment effects on a cellular level.

Patients and methods: Prospective, single-center pilot study at a university-based clinic of dermatology between January 1^st and August 30^th, 2016. Psoriatic lesions of 20 patients receiving dithranol treatment were assessed by RCM at baseline, day 4 and 8 of treatment.

Results: RCM measurements of psoriatic lesions receiving dithranol treatment revealed epidermal histomorphological changes with a strong median reduction of baseline hyperkeratosis by 45.0% (p < 0.001), acanthosis by 38.2% (p < 0.001), and epidermal thickness by 66.5% (p < 0.001) from baseline until day 8. Moreover, semiquantitative measurements of parakeratosis also showed a significant reduction until day 8 (p < 0.001). Correspondingly, RCM revealed dermal histomorphological changes with a decrease in diameter of dermal papillae by 32.1% (p < 0.001), decrease in diameter of papillary vessels by 16.9% (p = 0.002) and a strong semiquantitative reduction of the inflammatory infiltrate (p < 0.001).

Conclusions: Results from our pilot study indicate that topical dithranol treatment of psoriatic lesions may induce a rapid and marked reduction of pathologic epidermal and dermal RCM features.