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During a routine examination, a 30-year-old man is found to have diabetes mellitus. Hyperglycemia is controlled with diet and oral hypoglycemic agents until he is age 48, when insulin becomes necessary. At age 49, he notes continuous unpleasant burning paresthesias in both feet, which steadily worsen over the next several years. On examination at age 53, vibratory sensation (128 Hz) is absent at the toes and reduced at the ankles. Pinprick, light touch, and cold sensation are diminished in both feet, and light touch and pinprick produce an abnormal burning sensation in the soles. Position sense is normal. Tendon reflexes are normal at the knees and absent at the ankles. Strength is normal, as is the rest of the neurological examination.

Electrodiagnostic studies reveal normal motor nerve conduction velocities and needle electromyography in his legs and arms. Sensory nerve amplitudes are moderately reduced in the fibular and sural nerves and at the lower limit of normal in the median nerve. Sensory nerve conduction velocities are normal in the fibular, sural, and median nerves.

Over the next several years, despite vigorous control of his hyperglycemia, there is gradual progression of sensory loss in his legs, and his fingertips begin to feel numb. By age 62, he has erectile dysfunction and notices lightheadedness when he stands up quickly. Examination at this time reveals loss of vibratory sensation over his fingers, ankles, and knees. Pinprick, light touch, and cold sensation are markedly reduced below his knees and gradually become normal at mid-thigh; the same modalities are mildly reduced in his fingers. Rubbing his feet no longer produces discomfort. Position sense is mildly reduced in his toes and normal in his ankles and fingers; gait, including tandem, is normal. Tendon reflexes are absent in his legs and present in his arms. Strength is normal.

At electrodiagnostic study, sensory nerve amplitudes and conduction velocities are now unobtainable in his legs. In his arms, sensory nerve amplitudes are markedly reduced and sensory nerve conduction velocities are mildly reduced. Motor nerve conduction velocities are moderately reduced in his legs and normal in his arms; needle electromyography reveals evidence of denervation in muscles below the knees.


The peripheral nervous system consists of sensory, motor, and autonomic nerves, including cranial and spinal nerve roots, sensory and autonomic ganglia, and efferent and afferent nerve endings. The physiology of peripheral nerve axons includes anterograde rapid transport (400 mm/day) of vesicles and protein along neurotubules, mediated by the molecular motor protein kinesin; retrograde rapid transport (200 mm/day), also along neurotubules, of lysosomes and recycled membrane material (as well as exogenous material such as herpes virus, tetanus toxin, or growth factors); and, anterograde slow transport (0.2–3 mm/day) of neurofilament and neurotubule material (Figures 8–1 and 8–2). Large-diameter axons, including motor nerves and sensory A fibers mediating touch, vibration, and position ...

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