What is the role of imaging studies in the workup of multifocal motor neuropathy (MMN) with conduction block?

Updated: Nov 12, 2018
  • Author: Sasa Zivkovic, MD, PhD; Chief Editor: Nicholas Lorenzo, MD, MHA, CPE  more...
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Neuroimaging studies are not routinely performed in patients with suspected MMN.

Magnetic resonance imaging (MRI) of the brachial plexus may show an increased signal intensity on the T2-weighted images and nerve thickening of the nerve roots and proximal nerves of the arm, usually without contrast enhancement. The differential diagnosis of MRI findings includes radiation-related nerve injury and trauma, while tumors are usually associated with contrast enhancement.

Similar findings were reported with cranial nerve involvement.

In patients with MMN, neuromuscular ultrasound frequently shows enlargement of multiple nerves including cervical spinal roots and proximal arm nerves (rarely in proximal legs). [20]  Certain features, such as increased regional variance and asymmetric enlargement may help distinguish MMN from other chronic immune-related neuropathies. Similarly, the degree of spinal root and distal upper extremity nerve enlargement may help to distinguish MMN from ALS.

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