Novel acoustic evaluation system for scratching behavior in itching dermatitis: rapid and accurate analysis for nocturnal scratching of atopic dermatitis patients

Quantitative analysis of itching in patients with itching dermatitis including atopic dermatitis (AD) is indispensable for the evaluation of disease activity and response to therapy. However, the objective evaluation system for itching is limited. We have developed a new objective and quantitative scratching behavior detection system using a wristwatch-type sound detector. The scratch sound detected on the wrist is recorded on a personal computer through a filtering, squaring and smoothing process by specific hardware. Subsequently, the data is automatically processed and judged for the scratching movement using specific software based on the periodicity and energy of the signal. Twenty-four measurements for healthy volunteers and those with AD by this system were evaluated by comparison with a simultaneously recorded video analysis system. The ratio of scratching time in sleeping time evaluated by these two systems was almost identical. The healthy subjects scratched their skin approximately 2 min during 6 h of sleeping time, while the mean scratching time of AD subjects was 24 min in their sleeping time. In contrast to the time-consuming video analysis system, this system takes only several minutes for evaluation of an overnight record. This scratch sound detection system is expected to serve as a new objective evaluation tool for itching dermatitis, namely, AD, and development of anti-itch therapies for dermatitis.