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Abstract:
The velocity of impulse conduction was compared in peripheral nerve, spinal cord, and supraspinal segment of the somatosensory pathway in 15 diabetic subjects (mean age, 34.3 +/- 12.4 years) with little or no evidence of polyneuropathy, and in 15 age-matched normal controls. Motor and sensory conduction velocities (CVs) were slower in the diabetic subjects, and the latencies of F waves and somatosensory evoked potentials (SEPs) from arm and leg were longer (p less than 0.001 in each case), showing a relationship to duration of disease (0.51 less than lrl less than 0.84, p less than 0.001 in each case). Indirect estimates of spinal somatosensory conduction velocity (SSCV) were slower in the diabetic subjects (39.4 +/- 13.3 m/sec versus 54.2 +/- 10.5 m/sec, p less than 0.001), but conduction in the supraspinal segment (cervical cord to cortex) was identical in the two groups (5.6 +/- 1.3 msec versus 5.6 +/- 0.8 msec, p less than 0.1). In relationship to peripheral nerve CV, the incidence of subnormal SSCV in the diabetic subjects could not be fully explained on the basis of: (1) a passive consequence of peripheral neuropathy, (2) a sensory distal axonopathy, or (3) a primary diabetic myelopathy. We conclude that 40% of diabetics have subclinical electrophysiologic dysfunction of the posterior columns of the spinal cord, which may contribute to the lower-extremity sensory symptoms that are so prevalent in this disorder.