Sensory and motor peripheral nerve function and incident mobility disability

Abstract

Objectives: To assess the relationship between sensorimotor nerve function and incident mobility disability over 10 years.

Design: Prospective cohort study with longitudinal analysis.

Setting: Two U.S. clinical sites.

Participants: Population-based sample of community-dwelling older adults with no mobility disability at 2000/01 examination (N = 2,148 [Corrected]; mean age ± SD 76.5 ± 2.9, body mass index 27.1 ± 4.6; 50.2% female, 36.6% black, 10.7% with diabetes mellitus).

Measurements: Motor nerve conduction amplitude (poor <1 mV) and velocity (poor <40 m/s) were measured on the deep peroneal nerve. Sensory nerve function was measured using 10- and 1.4-g monofilaments and vibration detection threshold at the toe. Lower extremity symptoms included numbness or tingling and aching or burning pain. Incident mobility disability assessed semiannually over 8.5 years (interquartile range 4.5-9.6 years) was defined as two consecutive self-reports of a lot of difficulty or inability to walk one-quarter of a mile or climb 10 steps.

Results: Nerve impairments were detected in 55% of participants, and 30% developed mobility disability. Worse motor amplitude (HR = 1.29 per SD, 95% CI = 1.16-1.44), vibration detection threshold (HR = 1.13 per SD, 95% CI = 1.04-1.23), symptoms (HR = 1.65, 95% CI = 1.26-2.17), two motor impairments (HR = 2.10, 95% CI = 1.43-3.09), two sensory impairments (HR = 1.91, 95% CI = 1.37-2.68), and three or more nerve impairments (HR = 2.33, 95% CI = 1.54-3.53) predicted incident mobility disability after adjustment. Quadriceps strength mediated relationships between certain nerve impairments and mobility disability, although most remained significant.

Conclusion: Poor sensorimotor nerve function independently predicted mobility disability. Future work should investigate modifiable risk factors and interventions such as strength training for preventing disability and improving function in older adults with poor nerve function.

Keywords: disability; longitudinal analysis; muscle strength; older adults; peripheral nerve function.