What is the role of EMG in the workup of congenital myopathies?

Updated: Mar 11, 2019
  • Author: Matthew Harmelink, MD; Chief Editor: Amy Kao, MD  more...
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These studies test the electrical patterns of muscles and nerves. They can help to confirm the diagnosis, but results from these tests can be normal in a patient with congenital myopathy.  

The greatest value of EMG/NCS is to help exclude other causes of congenital myopathy. As such, these tests should be considered prior to a more costly, and invasive, muscle biopsy or focused genetic testing. EMG/NCS should be considered in all cases of congenital myopathy given that creatine kinase level is not typically suggestive of a muscle disease given its typically normal range of values.

In congenital myopathy, NCS findings can be normal or demonstrate low-amplitude responses in the motor nerve conduction studies in severe cases, while the EMG findings are either normal or show the typical small-amplitude, narrow-duration motor unit potentials (MUPs) that are seen in myopathies. Fibrillations and positive sharp waves are rare except in the more severe phenotypes.

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