Adverse effects of ultraviolet irradiation in atopic dermatitis.

The overall aim of this thesis was to evaluate adverse effects of ultraviolet irradiation (UV) in atopic dermatitis (AD). We focused on the two important adverse effects of UV: photosensitivity and skin cancer risk associated with calcineurin inhibitor treatment. In chapter 2 and 3 we found that photosensitivity affects approximately 3% of our AD population, being mainly females. Phototesting distinguishes two photosensitivity reaction patterns. Based hereupon, patients were diagnosed with photosensitive AD (PhAD) or AD with co-existing polymorphic light eruption (AD + PLE). Children with AD and photosensitivity showed the same two clinical reaction patterns as demonstrated in adults in the same 50-50% ratio. In chapter 4, we analyzed the inflammatory cell infiltrate after a single UVB irradiation in these two patient groups compared to non-photosensitive AD patients. There was no difference between the 3 groups concerning the influx of neutrophils, eosinophils and T-cells, the degranulation of mast cells or the quantity of epidermal dendritic cells. In chapter 5 we described a digital quantification method for immunohistochemical assessment of UV induced thymine cyclobutane pyrimidine dimers (TT-CPDs) in human skin. This method increased the linear measurement range compared to visual assessment and hence improved immunohistochemical quantification of DNA photo damage; it is more sensitive and efficient in measuring the extent of DNA-damage per nucleus. This method was eventually used to assess the difference in UV induced DNA damage repair in AD patients treated with either topical triamcinolone acetonide 0,1 % ointment (classic corticosteroid) or tacrolimus 0,1 % ointment (calcineurin inhibitor) described in chapter 6. Our study did not show differences in DNA damage repair rate of topical tacrolimus treated skin after a single UVB irradiation in human AD skin compared to non-treated or triamcinolone treated skin.