Use of a wrist activity monitor for the measurement of nocturnal scratching in patients with atopic dermatitis.

BACKGROUND

The amount of nocturnal scratching can be an indirect correlate of itch in pruritic dermatoses. We have previously used an infrared video camera to measure nocturnal scratching in atopic dermatitis (AD). Although this is a reliable method of measuring nocturnal scratching, it is not suitable for routine monitoring in clinical use.

OBJECTIVES

To find a simplified way of monitoring itch.

METHODS

We tried using a wrist activity monitor (ActiTrac) for the measurement of nocturnal scratching in patients with AD. ActiTrac is a wristwatch-shaped device that contains a piezoceramic sensor to measure and record limb movement over a pre-set time interval. The acceleration signal produced by motion of the hands is stored and downloaded into a personal computer. The average value of acceleration (AVA, 10(-3) g min(-1)) was calculated and compared with total scratching time as a percentage of total recording time (TST%) measured with the use of an infrared video camera in 63 recordings of 21 patients with AD. For 261 recordings in 29 patients with AD, the AVA was measured and correlated with disease severity, and compared with the AVA of five non-itchy controls.

RESULTS

There was a significant correlation between the AVA and TST% (r = 0.91, P < 0.001), and a regression equation of y = 0.44x - 2.5 was obtained. The AVA correlated well with the severity of AD and definitely differed from the results observed in normal controls. The AVA (mean +/- SD) was 44.4 +/- 19.1 for 115 recordings in patients with severe AD, 23.2 +/- 10.9 for 89 recordings in patients with moderate AD, 8.9 +/- 6.0 for 57 recordings in patients with mild AD and 4.1 +/- 1.9 for 25 recordings in five normal controls. The units used here are arbitrary units min-1 with a range of 0--250, which corresponds to 0-75 x 10(-6) g min(-1).

CONCLUSIONS

A wrist activity monitor is able to measure nocturnal scratching. However, further methods of analysis should be sought to select scratching activity exclusively.