Which nerve conduction study findings are characteristic of diabetic neuropathy?

Updated: Jan 08, 2019
  • Author: Dianna Quan, MD; Chief Editor: Romesh Khardori, MD, PhD, FACP  more...
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Answer

Findings on nerve conduction studies depend on the pattern of nerve damage. Patients with distal symmetrical sensorimotor polyneuropathy from predominant axonal loss have reduced or absent sensory nerve action potentials, especially in the legs. With progression of neuropathy, compound motor action potential amplitudes may also be reduced and abnormalities may be observed in the hands. These changes reflect length-dependent degeneration of large-diameter myelinated nerve fibers.

Conduction velocities are generally within the normal range or only mildly slowed in distal symmetrical polyneuropathy. If conduction velocities are less than 70% of the lower limit of normal, or if conduction block is present, the patient may have superimposed peripheral nerve demyelination in addition to the more typical axonal loss seen in distal symmetrical polyneuropathy. Generalized demyelinating changes on nerve conduction studies should prompt further evaluation for CIDP. Focal slowing of conduction velocity at common sites of entrapment may indicate one of the mononeuropathy syndromes discussed above.

In patients with diabetes, nerve conduction study abnormalities may be found even in the absence of clinical symptoms of polyneuropathy. In a prospective study by Walter-Höliner et al of 38 children and adolescents with type 1 diabetes, clinical neurologic examination revealed diabetic peripheral neuropathy in 13.2% of the group, compared with 31.6% of patients when diagnosis was made using nerve conduction velocity testing. Thus, the latter test demonstrated the widespread existence of subclinical diabetic peripheral neuropathy in the study’s patients. [66]


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