Age-Related Changes in Neurologic Examination and Sensory Nerve Amplitude in the General Population: Aging of the Peripheral Nervous System

Abstract

Background and objectives: Chronic axonal polyneuropathy is a common disease of the peripheral nervous system with increasing prevalence with age. Typical neurologic signs are present in patients with polyneuropathy but may also occur in individuals without disease. Owing to limited knowledge on normal aging of the peripheral nervous system, it can be difficult to distinguish peripheral nerve dysfunction due to disease from variations in normal aging. Therefore, we described the changes in neurologic examination and nerve conduction studies that accompany aging in the general population.

Methods: In this cross-sectional population-based study, we screened participants for chronic polyneuropathy in a controlled environment using standardized methods including a symptom questionnaire, neurologic examination, and nerve conduction studies (NCS). Inclusion criteria were 40 years or older and living in a suburb of Rotterdam, the Netherlands. Participants not diagnosed with chronic polyneuropathy, based on the discussion of findings in the screening by an expert team, were included to determine the effect of age (range 41-96 years) on features of neurologic examination and NCS using frequency calculations and quantile regression analysis.

Results: In total, 4,179 participants (mean age 64.5 ± 12.7 years, 54.9% female) were included of whom 3,780 (90.5%) did not fulfil the criteria for polyneuropathy. In the population without polyneuropathy, the frequency of normal features at neurologic examination declined with age, most pronounced for vibration sense at the hallux (from 6.6 [SD ± 1.5] in 40-49 years to 3.6 [SD ± 3.1] in 80 years or older) and Achilles tendon reflexes (absent in 9% in 40-49 years up to 33% in 80 years or older). Superficial pain sensation and patellar tendon reflexes remained stable over time. Sural sensory nerve action potential (SNAP) amplitude declined with age from 11.2 μV in 40-49 years to 3.3 μV in 80 years or older. Nonrecordable SNAP amplitudes were found in 25.1% of the participants older than 80 years, more often in men (30.3%) than in women (21.0%).

Discussion: This study showed the effect of age on features of neurologic examination and sural nerve amplitude in the general population. These findings are helpful to distinguish features suggesting polyneuropathy from variations of normal aging of the peripheral nervous system.

Figure 1. Presence of Features of Neurologic Examination per Age Decade in the Population Without Chronic Polyneuropathy

Frequency of presence of Achilles tendon reflex (orange), patellar tendon reflex (red), superficial pain sensation (blue), and vibration sense (yellow). The presence of neurologic features comprised normal or minimal tendon reflexes, normal superficial pain sensation on the feet, and vibration sense ≥4 using the graduated tuning fork (0–8).

Figure 2. Details per Component of Features of Neurologic Examination per Age Decade in the Population Without Chronic Polyneuropathy

Frequency of signs of neurologic examination of tendon reflexes, superficial pain sensation, and vibration sense, classified as normal (“normal,” “7–8), minimal (“minimal,” “from toes to ankle,” “4–6”), or abnormal (“absent,” “from toes to tibia or higher,” “0–3”).

Figure 3. Percentile Curves of Sural Sensory Nerve Action Potential Amplitude in the General Population Without Chronic Polyneuropathy, Stratified for Sex

Percentile curves for the sural sensory nerve action potential amplitude for female (panel A, N = 1,783) and male participants (panel B, N = 1,372). Lines correspond to the 5th (orange), 10th (black), 25th (black), 50th (red), 75th (black), 90th (black), and 95th (orange) percentile.