Estimation error of the body surface area in psoriasis: a comparative study of physician and computer-assisted image analysis (ImageJ)

Abstract

Background: Assessing the area involved in a skin disease, i.e. the body surface area (BSA), is essential in diagnosing disease severity, including in psoriasis. However, in psoriasis, BSA tends to be overestimated by physicians and has shown high inter-rater and intrarater variability. Furthermore, there are no reports suggesting the cause and clinical significance of overestimating BSA in psoriasiss. Aim: To investigate the errors in estimating BSA in psoriasis by comparing physicians' results with those of computer-assisted image analysis (CAIA) and to provide suggestions regarding the clinical implications of such errors. Methods: Using 43 images, 36 physicians visually estimated BSA in psoriasis, and subsequently, the images were evaluated using a CAIA program (ImageJ); the BSA values determined by the physicians and CAIA were then compared and matched. The BSA percentage was also graded on a scale from 0 to 6, as follows: Grade 0 = no lesion, Grade 1 = 1%–9%, Grade 2 = 10%–29%, Grade 3 = 30%–49%, Grade 4 = 50%–69%, Grade 5 = 70%–89% and Grade 6 = 90%–100%. Each grade range was divided, with the bottom and top 50% defined as the ‘first half’ and ‘second half,’ respectively. Results: The mean proportion of correct assessments by physicians was 49.4%. Physicians tended to overestimate the BSA of psoriatic lesions by 8.76% ± 8.82% compared with CAIA. The largest estimation error (proportion incorrect 75.7%) was observed in Grade 3 (30%–49% involvement). Estimates in the second half of the range demonstrated a higher proportion of inaccuracies compared with those in the first half. An overestimating error occurred in certain morphological characteristics of the psoriatic lesions. Conclusions: The inaccuracy of BSA estimation by physicians may be related to the fact that information from the human eye is perceived to be exaggerated compared with the actual size. Further research into using artificial intelligence technology is needed to reduce quantification error and develop an ideal BSA assessment system. Additionally, education and training are needed for physicians to measure BSA accurately. © 2022 British Association of Dermatologists.