Multi Focal Motor neuropathy


Multifocal motor neuropathy (MMN)

Multifocal motor neuropathy (MMN) and motor syndromes with serum anti-GM1 antibodies.
A. Clinical Syndromes
The immune-mediated motor neuropathies are characterized by asymmetric, slowly progressive weakness that most commonly begins in the hands & arms. The age of onset is generally between 20 and 75. Men are affected somewhat more commonly than women. Motor findings include asymmetric weakness and variable degrees of atrophy. Patients with prominent conduction block may present with weakness in muscles with relatively normal bulk. Rarely, patients have had cranial nerve signs including external ophthalmoplegia and unilateral tongue weakness and atrophy. Some patients report paresthesias, but sensory signs are usually absent or clinically insignificant. In regions with normal strength tendon reflexes are often preserved. In areas of weakness, reflexes may initially be normal but can become reduced with progression of the disease. Fasciculations are not uncommon, and may add to diagnostic confusion between MMN and variants of amyotrophic lateral sclerosis (ALS) with only lower motor neuron signs. However, hyperreflexia and spasticity typical of ALS never occur in MMN


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Conduction block
Amount of block increases with
more proximal stimulation.
  • Electrodiagnostic Classification below is a conduction block, amplitude reduction in distal segement.
     conduction block
  • 1) Patients with MMN have, by definition, focal block of nerve conduction along the course of motor, but not sensory, axons. Conduction block has been variably defined as a 15% to 50% reduction in the compound muscle action potential at proximal as compared with distal sites of stimulation. Conduction block may go undetected unless multiple segments in several nerves are tested. The finding of conduction block is most reliable when the change is focal and in a distal nerve segment other than regions of entrapment. Temporal dispersion and phase cancellation over long nerve segments should be ruled out. In MMN, motor conduction velocities and distal latencies are often unremarkable in regions without conduction block. Sensory studies are normal.
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