Laser Doppler perfusion imaging (LDPI) and transepidermal water loss (TEWL) values in psoriatic lesions treated with narrow band UVB phototherapy. Dermal vascularity may be useful indicator of psoriatic activity.

OBJECTIVE

This study attempts to objectively measure physiological changes in transepidermal water loss (TEWL), an indicator of skin barrier function and laser Doppler perfusion index (LDPI) an indicator of skin vascularity, of psoriatic skin lesions following treatment to narrow-band ultraviolet B (UVB) phototherapy using the psoriasis severity (PS) score as a measurement of clinical phototherapy response.

MATERIALS AND METHODS

Fourteen patients with established diagnosis of plaque type psoriasis were studied. The patients received narrow band UVB phototherapy 3 times a week until clearance of their psoriasis and the frequencies are reduced as clearance is observed. Two psoriasis plaques ("lesional skin") were used to measure treatment response and another 2 areas of uninvolved ("non-lesional skin") on the corresponding opposite limbs were identified for comparison. PS score, TEWL and LDPI were carried out at baseline (0 week), 2 weeks and 8 weeks during treatment. Measurements were carried out just before each phototherapy session and repeated 1 hour after phototherapy treatment.

RESULTS

The mean PS score decreased by almost 40% after 2 months phototherapy (t = 2.44, P = 0.028). There was no significant difference in PS score between week 0 and week 2, or between week 2 and week 8. After phototherapy, there was no significant difference in LDPI values on the psoriatic lesional skin between week 0 and week 8 or between week 2 and week 8. It appears that phototherapy does not induce inflammation on non-lesional skin to provoke measurable LDPI changes. The mean TEWL values of psoriatic lesional skin were significantly higher than normal skin throughout the study period before and during phototherapy (week 0, t = 5.71, P = 0.000, week 2, t = 9.29, P = 0.00, week 8, t = 6.93, P = 0.000). It appears that the skin barrier function of psoriatic skin improves only minimally as psoriatic lesions improve clinically (as evidenced by the reduction in PS scores) with narrow-band UVB phototherapy, but the dermal vascularity and blood flow and barrier function of the psoriatic skin remained abnormal.

CONCLUSION

It appears that LDPI and TEWL measurement may not be a good surrogate marker of clinical response to narrow-band UVB phototherapy.