What is the role of nerve conduction studies in the workup of focal muscular atrophy (FMA)?

Updated: Feb 20, 2018
  • Author: Sridharan Ramaratnam, MD, MBBS; Chief Editor: Helmi L Lutsep, MD  more...
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These studies may reveal evidence of peripheral nerve involvement: mononeuropathy, nerve entrapment, diabetic amyotrophy, and brachial or lumbosacral plexopathies.

The abnormalities may include prolonged distal latencies, slowed conduction velocities, reduced amplitude of CMAPs, and evidence of conduction block.

The F responses and H reflex studies may be useful in assessing proximal root lesions.

Disuse muscular atrophy from immobilization also is associated with a significant reduction in CMAP amplitude, which may vary according to muscle site and function.

Unlike other motor neuron diseases, including the spinal muscular atrophies, in Kennedy disease, diffusely low amplitude or absent SNAPs may occur, despite normal sensation on clinical examination.

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