A comparison between BSA, PASI, PLASI and SAPASI as measures of disease severity and improvement by therapy in patients with psoriasis

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 <= 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.