Are accelerometers a useful tool for measuring disease activity in children with eczema? Validity, responsiveness to change, and acceptability of use in a clinical trial setting

Background: Actigraphy, which uses accelerometers to record movement, has been proposed as an objective method of itch assessment in eczema. Previous studies have found strong correlations with actigraphy and video surveillance, disease severity and biological markers in patients with eczema.

Objectives: To assess the validity of accelerometer data, its responsiveness to change and the practicality and acceptability of accelerometers when used as an outcome measure in a clinical trial.

Methods: This study used data collected from 336 participants of the Softened Water Eczema Trial (SWET). Accelerometer data were compared with three standardized scales: Six Area, Six Sign Atopic Dermatitis (SASSAD) severity score, Patient Oriented Eczema Measure (POEM) and Dermatitis Family Impact (DFI). Spearman's rank testing was used for correlations.

Results: Only 70% of trial participants had complete data, compared with 96% for the primary outcome (eczema severity - SASSAD). The convergent validity of accelerometer data with other measures of eczema severity was poor: correlation with SASSAD 0·15 (P = 0·02) and POEM 0·10 (P = 0·13). Assessing for divergent validity against quality of life measures, the correlation with the DFI was low (r = 0·29, P < 0·0001). Comparing the change scores from baseline to week 12 for SASSAD, POEM and DFI with the change in accelerometer scores we found low, negative correlations (r = -0·02, P = 0·77; r = -0·12, P = 0·06; and r = -0·01, P = 0·87, respectively). In general, the units were well tolerated but suggestions were made that could improve their usability in children.

Conclusions: Actigraphy did not correlate well with disease severity or quality of life when used as an objective outcome measure in a multicentre clinical trial, and was not responsive to change over time. Further work is needed to establish why this might be, and to establish improved methods of distinguishing between eczema-related and eczema-nonrelated movements.