Ratios of nerve conduction parameters in proximal to distal limbs remain constant through the second to the eighth decades.

We investigated the effect of age on nerve conduction parameters to establish a diagnostic validity in demyelinating neuropathies of the aged. We evaluated 257 subjects (age 10-76 years old) with no history or signs of peripheral neuropathies. The CMAP amplitude ratio (proximal CMAP/distal CMAP), duration ratio, and area ratio were almost the same throughout the second to eighth decades. The respective lower limits of the normal CMAP amplitude ratio (mean-3 SD) were 0.79 (median nerve), 0.75 (ulnar nerve), 0.57 (peroneal nerve), and 0.45 (tibial nerve). The upper limits of the normal CMAP duration ratio (mean +3 SD) were 1.21 (median nerve), 1.22 (ulnar nerve), 1.37 (peroneal nerve), and 1.35 (tibial nerve). The lower limits of the normal CMAP area ratio (mean-3 SD) were 0.81 (median nerve), 0.78 (ulnar nerve), 0.60 (peroneal nerve), and 0.57 (tibial nerve). No age-related changes were observed in the amplitude ratio or duration ratio SNAP, although the standard deviation increased with age. Since the amplitude, duration and area ratios are easily calculated and age-independent, they can provide useful and reliable information on aged patients with demyelinating neuropathies by conventional nerve conduction studies.