Dithranol (known in the U.S.A. as anthralin and in Germany as cignolin) is one of the oldest and safest topical anti-psoriatic treatments. However, despite explorative investigations, the skin disease-clearing mechanisms of dithranol remain poorly understood (Painsi et al, JDDG 2015). The purpose of this study is to investigate the therapeutic mechanisms of dithranol in psoriasis.

Skins biopsies from psoriatic skin and blood samples will be taken before (day 0) and at several time points after start (day 4, week 2-3, and week 6-7) of dithranol therapy to be subjected to an explorative analysis (see outcome measures). A total of maximal 15 psoriasis patients will be enrolled. Normal lesion-adjacent skin from 10 patients undergoing surgery for non-inflammatory conditions will serve as control.

Inclusion Criteria:

• Males and females over 18 years of age
• Clinical diagnosis of chronic plaque psoriasis
• Dithranol treatment scheduled

Exclusion Criteria:

• Systemic anti-psoriatic therapy (DMARD, phototherapy and/or Biologics) within 4 weeks of study entry (start of dithranol treatment)
• Topical treatment with steroids and or vitamin D3 analogues within 2 weeks of study entry (start of dithranol treatment)
• Autoimmune disorders
• Poor general health status
• Intolerance of dithranol
• Pregnancy and lactation period

A total of maximal 15 psoriasis patients will be enrolled. Normal lesion-adjacent skin from 10 patients undergoing surgery for non-inflammatory conditions will serve as control.