However, electrodiagnostic studies can never truly tell whether there is axon transection or not.ĮMG testing can be used to demonstrate neurological recovery. The limitation here is that one can not differentiate a conduction block where the nerve/axon remains intact from axonal degeneration or from nerve/axon transection. Nerve conduction studies across an injured segment of nerve will also be abnormal immediately.
These early findings can help to localize the site of injury and to some extent the degree of injury. However, when there is significant axonal injury or even a severe neuropraxia (conduction block), a decreased rate of motor unit recruitment will instantaneously become abnormal and a skilled electromyographer can often determine this. This is a length-dependent process so that the longer the length of the injured axon, the longer Wallerian degeneration will take. It is true that the degree of muscle denervation that occurs after nerve injury can not be determined until Wallerian degeneration is complete and this can take as short as 1 week or as long as 4 weeks. One of the most common myths about EMG tests is that one must wait 2–3 weeks following a nerve injury before reliable information can be obtained.
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