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Smartwatch-Derived Nocturnal Scratching Metrics Capture Disease Activity and Severity in Pediatric Atopic Dermatitis
Fumiko Iwai1,2, Takahiro Nishida1,2, Rei Kanai1,2
1Allergy Center, National Hospital Organization (NHO) Mie National Hospital, Tsu 514-0125, Japan.
Insights
Smartwatch data can objectively track nocturnal scratching in children with atopic dermatitis (AD), offering a reliable digital biomarker for disease activity and treatment response.
Area of Science:
- Dermatology
- Biomedical Engineering
- Digital Health
Background:
- The itch-scratch cycle significantly worsens atopic dermatitis (AD) in children.
- Objective monitoring is crucial, but patient-reported itch scores are often unreliable in pediatric populations.
- This study explores smartwatch-derived scratching metrics as objective biomarkers for AD.
Purpose of the Study:
- To evaluate smartwatch-derived nocturnal scratching metrics as digital biomarkers for disease activity in pediatric atopic dermatitis (AD).
- To assess the utility of these metrics in reflecting treatment response during topical therapy initiation.
- To determine the association between scratching metrics and established clinical and biochemical markers of AD.
Main Methods:
- Prospective observational study involving 50 children with physician-diagnosed AD.
- Participants wore an Apple Watch with the Itch Tracker app for 5-14 nights.
- Analyzed scratch count rate (SCR), scratch duration ratio (SDR), and scratch burden index (SBI), correlating them with Eczema Area and Severity Index (EASI), Patient-Oriented Eczema Measure (POEM), serum TARC, and itch NRS.
Main Results:
- All nocturnal scratching metrics (SCR, SDR, SBI) showed significant correlations with baseline Eczema Area and Severity Index (EASI) and serum TARC.
- Decreases in scratching metrics closely paralleled clinical improvements in AD.
- The scratch burden index (SBI) demonstrated the best discriminative performance in logistic regression models for identifying treatment responders (AUC = 0.78).
Conclusions:
- Wearable-derived nocturnal scratching metrics demonstrate moderate, consistent associations with pediatric atopic dermatitis (AD) severity and short-term treatment response.
- These digital biomarkers show potential as objective, treatment-responsive measures for AD.
- Further prospective validation is necessary to establish their clinical utility in real-world pediatric AD monitoring.
Abstract:
Background/Objectives: The itch-scratch cycle is a key driver of exacerbation in atopic dermatitis (AD) and requires objective monitoring, yet patient-reported itch scores are often unreliable in children. This study aimed to evaluate smartwatch-derived nocturnal scratching metrics as digital biomarkers of disease activity and treatment response in pediatric AD. Methods: In this prospective observational study, 50 children (median age 9 years) with physician-diagnosed AD wore an Apple Watch with the Itch Tracker application for 5-14 nights during initiation of topical therapy. Three scratch metrics-scratch count rate (SCR), scratch duration ratio (SDR), and scratch burden index (SBI, duration × intensity)-were analyzed. Associations with clinical outcomes [Eczema Area and Severity Index (EASI), Patient-Oriented Eczema Measure (POEM)], serum thymus and activation-regulated chemokine (TARC), and itch numerical rating scale (NRS) were examined. Logistic regression models were evaluated to examine whether these metrics could identify children who achieved clinically meaningful improvement, defined as EASI-50 plus ≥ 4-point POEM reduction. Results: All scratch metrics correlated with baseline EASI (r = 0.60-0.64, p < 0.001) and serum TARC (r = 0.58-0.60, p < 0.001). Reductions in scratching paralleled clinical improvement (r = 0.67-0.71, p < 0.0001). Among models, the SBI-based logistic regression demonstrated the best discriminative performance (AUC = 0.78, 95% CI: 0.64-0.92). Conclusions: Wearable-derived nocturnal scratching metrics showed moderate but consistent associations with disease severity and short-term improvement. Although predictive capability remains to be established, these metrics may serve as treatment-responsive digital measures. Given the cross-sectional nature of biomarker analyses and other study limitations, further prospective validation is required before clinical application in real-world pediatric AD monitoring.
