Sensory and motor correlates of frailty: dissociation between frailty phenotype and frailty index

Background: Frailty has been associated with a decline in sensory and motor function. However, given that different frailty measures were shown to overlap but also differ in their diagnostic properties, sensory and motor correlates of frailty might be different depending on the operationalization of frailty. Our objective was to identify sensory and motor determinants of frailty and compare the results between frailty phenotype (FP) and frailty index (FI). Methods: Data from 44 pre-frail and frail subjects aged 65 and above were used. Frailty was measured using the FP and the FI. Sensory function in the visual, auditory, and tactile domain was assessed using visual acuity, absolute hearing threshold and mechanical detection threshold. Upper extremity motor performance was evaluated by the Purdue Pegboard Test and the Short Physical Performance Battery was used to assess lower extremity motor function. Multiple logistic regression models were employed to determine associations of sensory and motor function with frailty vs. pre-frailty for both frailty measures. Results: The frailty measures were moderately correlated (0.497, p <= 0.01) and had a Kappa agreement of 0.467 (p = 0.002). Using the FP, frailty was significantly associated with reduced upper extremity motor function only (OR = 0.50, 95% CI 0.29-0.87, p = 0.014). Frailty as assessed by the FI was significantly related to higher hearing thresh-olds (OR = 1.21, 95% CI 1.02-1.43, p = 0.027) and reduced lower extremity performance (OR = 0.32, 95% CI 0.13-0.77, p = 0.012). Conclusion: Frailty is related to reduced performance in measures of sensory and motor function. However, traditional measures of frailty might be differentially sensitive to capture sensory and motor decline, possibly contributing to the much-observed discordance between the diagnostic instruments. This should be taken into account by researchers and clinicians when planning and evaluating therapeutic interventions for frailty.