This study examined nerve conduction velocities in proximal and distal nerve segments among healthy elderly participants. The researchers found that proximal segment conduction velocities declined significantly with age only in men, slowing approximately 4.0 m/s per decade. In contrast, distal segment velocities did not decline significantly with age for either men or women. The results suggest there are sex-specific declines in myelin function in the peripheral nervous system that are related to the aging process.

1. Decline in conduction velocity with age occurs in the proximal segments among the
healthy elderly
Johmn Engstrom, Chris Songster, Amy Lee, Carol Piunti, Ari Green
Department of Neurology, University of California, San Francisco
Methods:
• 104 of 156 participants underwent bilateral upper extremity motor and
sensory NCS (median and ulnar) and lower extremity sensory NCS
(sural). Nerve segments with known or clinically identifiable
neuropathy were excluded, by history or exam, with final sample of 93
with complete data.
• Cold limbs were warmed to at least 32˚C.
• Distal stimulations were performed on sensory NCS.
• Proximal and distal stimulations were performed on motor NCS. For
the median nerve, CV of two nerve segments (wrist-elbow (W-E),
elbow-axilla (E-A)) were calculated. For the ulnar nerve, CV of three
nerve segments (wrist-below elbow (W-BE), below elbow-above elbow
(BE-AE), above elbow-axilla (AE-A)) were calculated.
Figure 1: Diagram of motor NCS. Blue represents median nerve and red
represents ulnar nerve, with x’s representing recording sites (median = APB,
ulnar = ADM) and dots representing stimulation sites. Nerve segments are
abbreviated by the stimulation sites. Diagram not drawn to scale.
Data analysis:
•Principal component analysis (PCA) is a statistical method for
combining correlated data that also adjusts the relative contribution of
each single variable via a weighting mechanism . PCA was performed
using the variance-covariance matrix separately for proximal segments
(median E-A, ulnar BE-AE, ulnar AE-A) and distal segments (median
W-E, ulnar W-BE) CV, combining left and right sides.
•Principal component 1 (PC1) is the linear combination of the original
variables accounting for the largest amount of variance in the data. For
each individual, a composite score for proximal and distal segments
was calculated using weights derived from PC1. This score represents
a weighted average of the proximal and distal CV for that individual.
•Multivariate linear regression was used to determine the effects of age
on proximal and distal CV composite scores, adjusting for sex, height,
weight. An age-sex interaction was also included in the model.
Temperature was not a confounder in linear regression of individual
nerve segments, and not included in the model with composite scores.
•Sensitivity analysis was performed excluding the ulnar BE-AE
segment in the proximal composite score CV analysis.
Results Discussion
•These studies revealed associations between
age and lower conduction velocities for
proximal nerve segments among men in a
population selected for outstanding overall
health.
•Suggests a sex specific process driven by
“aging”, independent of other disease
states.
•Age explains 21% of the variance observed in
proximal NCV
•This data agrees with our previous findings
presented Platform #S09.005 at 2009 AAN from
the same cohort showing a correlation between
age and mfVEP latency in men only; (r=0.30,
p=0.001).
•Implies that there may be shared sex specific
age related declines in myelin function for both
CNS and PNS.
•Future directions involve further correlations
with other measures, including neuroimaging
and genetic analysis.
References
Falco FJE, Hennessey WJ, et al. Standardized
nerve conduction studies in the upper limb of
the healthy elderly. American Journal of
Physical Medicine and Rehabilitation. 1992,
71:263-71.
Rivner MH, Swift TR and K Malik. Influence of
age and height on nerve conduction. Muscle
Nerve 2001; 24: 1134-1141.
Robinson LR, Rubner DE et al. Factor
Analysis: A methodology for data reduction in
nerve conduction studies. Am J Phys Med
Rehabil 1992; 71:22-27.
Stetson DS, Albers JW et al. Effects of age,
sex, and anthropometric factors on nerve
conduction measures. Muscle & Nerve 1992;
15:1095-1104.
Introduction
• Increasing age has been associated with slower nerve conduction
velocity (NCV) after middle age, especially in distal nerve segments.
Most of these series have included patients with clinical conditions
known to impact NCV (such as diabetes or alcoholism), and few have
looked specifically in an elderly population.
•The Myelin and Aging cohort is a healthy community dwelling
population between age 60 and 90 who undergo extensive
neurological phenotyping (fMRI, structural MRI, mfVEP, NCV, reaction
time testing, laboratory studies, and genetic analysis).
•Inclusion criteria consist of a Clinical Dementia Rating (CDR) of 0,
MMSE > 27, and no report of significant cognitive decline in the
previous year.
•General exclusion criteria were any major medical illness including
hypertension, cardiovascular disease, or cognitive impairment.
•Specific exclusion criteria for NCV include history of neuropathy as
well as known risk factors for neuropathy.
Figure 3: Scatter plot of (a) distal and (b) proximal nerve segment
composite scores with age, for men and women. Composite scores
represent the weighted averaged of the conduction velocity of the
distal or proximal segments for that individual. Proximal conduction
velocities decline by about 4.0 m/s per decade only for men
(p<0.001).
b
a
Table 3 Linear regression of distal and proximal
nerve segment composite scores with age
The age coefficient can be interpreted as m/s change per year.
There was a strong interaction between age and sex, with the
proximal nerve segment composite score changing significantly with
age only in men at p<0.05 level. Although the ulnar below elbow-
above elbow (BE-AE) segment was designated a proximal segment
a priori, a sensitivity analysis excluding this segment from the
proximal composite score showed a similar decline in only men.
Two alternative methods of creating composite scores, using
averages with equal weights and summing up standardized values,
produced similar results. Adjustments for height and weight did not
affect results.
Table 1 Mean age of myelin and aging cohort
Mean age of all subjects in cohort undergoing nerve conduction
studies compared with subjects with complete nerve conduction
studies of median and ulnar nerves bilaterally.
Table 2 Mean nerve segment conduction velocities
Mean conduction velocities of nerve segments of subjects in
cohort undergoing nerve conduction studies compared with
subjects with complete nerve conduction studies of median and
ulnar nerves bilaterally. Means were similar in both groups for
all nerve segments. W-E wrist-elbow, E-A elbow-axilla, W-BE
wrist-below elbow, BE-AE below elbow-above elbow, AE-A
above elbow-axilla.
Figure 2: Myelin and Aging Cohort