Background: This study investigates four measures of disease severity in patients with psoriasis, both before and after therapy.
Methods: Data records were analyzed from 33 patients with moderate-to-severe chronic plaque psoriasis who were treated with efalizumab, 1 mg/kg/week subcutaneously, for 12 weeks. Four measures of disease severity were used: body surface area (BSA), psoriasis area and severity index (PASI), psoriasis log-based area and severity index (PLASI) and self-administered PASI (SAPASI).
Results: At the end of the 12-week therapy, the mean percent improvement shown by each measure varied considerably, ranging from 48.6% (PASI) to 70.6% (SAPASI). PASI and PLASI were the most comparable (67.3% and 66.5%). These differences were smaller when a dermatologist's opinion about the improvement was taken into account, for example "very good improvement" ranged from mean percent improvement of 63.8% (BSA) to 83.8% (PASI). The correlation between all measures revealed a high level of significance (P<or= 10(-5)).
Conclusions: Comparing the slopes and intercepts of the regression lines revealed PLASI as the most reliable measure for the severity and therapeutic improvement in patients with moderate-to-severe chronic plaque psoriasis. PLASI proved to be a marginally more accurate than PASI, and much more accurate than SAPASI and BSA. The superiority of PLASI may be a result of the logarithmic scale of the affected skin surface.