BACKGROUND
Average daily steps (avDS) could be a valuable indicator of real-world ambulation in people with Parkinson’s disease (PwPD) and previous studies reported the validity and reliability of this measure. Nonetheless, no study to date has considered disease phenotype, stage and severity when assessing reliability of consumer wrist-worn devices to estimate daily step count in unsupervised, free-living conditions in PwPD.
OBJECTIVE
To assess and compare the reliability of a consumer wrist-worn smartwatch (Garmin Vivosmart 4) in counting avDS in PwPD in unsupervised, free-living conditions among disease phenotypes, stages, and severity groups.
METHODS
One-hundred-four PwPD were monitored through Garmin Vivosmart 4 for 5 consecutive days. Total daily steps for each day were recorded and avDS were calculated. PwPD were dichotomized into tremor dominant (TD) (N=39) or postural instability and gait disorder (PIGD) (N=65), presence (N=57) or absence (N=47) of tremor, and mild (N=65) or moderate (N=39) disease severity. Based on modified Hoeh and Yahr scale (mHY), PwPD were further dichotomized into earlier (mHY 1-2) (N=68) or intermediate (mHY 2.5-3) (N=36) disease stage. Intraclass correlation coefficient (ICC) (3, k), standard error of measurement (SEM) and minimum detectable change (MDC) were used to evaluate the reliability of avDS for each subgroup. The threshold for acceptability was set at an ICC ≥ 0.8 with a lower bound of 95% confidence interval (CI) ≥ 0.75. Student’s t-tests for independent groups and analysis of 83.4% CI overlap were used to compare ICC between each group pair.
RESULTS
Reliability of avDS measured through Garmin Vivosmart 4 for 5 consecutive days in unsupervised, free-living conditions was acceptable in the overall population with an ICC of 0.89 (0.85-0.92), SEM% below 10% and an MDC of 1580 steps/day (27% of criterion). In all investigated subgroups, reliability of avDS was also acceptable (ICC range 0.84-0.94). However, ICCs were significantly lower in PwPD with tremor (P=.030), with mild severity (P=.040) and earlier stage (P=.003). Moreover, SEM% was below 10% in PwPD with PIGD phenotype, without tremor, moderate disease severity and intermediate disease stage, with a MDC ranging from 1148 to 1687 steps/day (18-25% of criterion). Conversely, in PwPD with TD phenotype, tremor, mild disease severity and earlier disease stage, SEM was >10% of criterion and MDC values ranged from 1401 to 2263 steps/day (30- 33% of the criterion).
CONCLUSIONS
In mild-to-moderate PwPD, avDS measured through a consumer smartwatch in unsupervised, free-living conditions for 5 consecutive days are reliable irrespective of disease phenotype, stage, and severity. However, in PwPD with TD phenotype, tremor, mild disease severity and earlier disease stages, reliability could be lower. These findings could facilitate a broader and informed implementation of avDS as an index of ambulatory activity in PwPD.
