Development of a digital image analysis system for objective evaluation of treatment response in cellulitis

Cellulitis is a common skin infection. While changes in lesion color are valuable indicators of treatment efficacy, assessments often rely on subjective judgments. To provide an objective method for evaluating treatment response, we developed a digital imaging system that quantifies red, green, and blue (RGB) values of lesions and calculates the RGB distance between lesions and normal skin. We analyzed 34 patients with cellulitis treated between 2022 and 2025. Clinical images were obtained on days 1 (baseline), 3, 7, and 14. By day 14, the G and B values of lesions increased significantly (G: 115.6 to 135.7, B: 91.8 to 105.5; P < 0.05), while the R values remained stable. The RGB distance decreased significantly from day 3 (64.3 to 53.7; P < 0.05). Patients were classified by Investigator's Global Assessment into Group A (favorable clinical outcome, n = 13) and Group B (delayed clinical improvement, n = 21). Receiver operating characteristic analyses of the RGB distance ratio relative to day 1 showed high accuracy at day 3 (cut-off = 0.62) and day 7 (cut-off = 0.48). A significantly higher proportion of Group B patients had a history of edema. These findings suggest our system provides an objective method for evaluating the clinical course of cellulitis.