What Is Multifocal Motor Neuropathy?

Multifocal motor neuropathy (MMN), also known as multifocal demyelinating motor neuropathy, is a chronic multiple mononeuropathy mainly involving motor nerves. It is a rare demyelinating peripheral neuropathy. Its clinical manifestations are progressive asymmetric limb weakness, with distal involvement mainly. The electrophysiological feature is a persistent multifocal conduction block on the motor nerve.

Basic Information

nickname: Multifocal demyelinating motor neuropathy
Multiple groups: 20 to 80 years old, more common in men

Common locations: Motor nerve
Common symptoms: Progressive asymmetric limb weakness, mainly distal involvement
Contagious: no

Causes of multifocal motor neuropathy

Little is known about the cause of the disease. At present, it is speculated that it may be related to Campylobacter jejuni infection, and the lipopolysaccharide component (LPS) of Campylobacter jejuni may induce the production of anti-ganglioside antibodies. There are at least two points of evidence that the occurrence of this disease is related to autoimmunity. One is that the serum anti-ganglioside GM1 antibody is elevated in some patients, and the other is that a considerable number of patients have immunosuppressive drugs (immunoglobulin and cyclophosphamide for intravenous use) The treatment is effective.

Clinical manifestations of multifocal motor neuropathy

The disease occurs frequently in the age of 20 to 80 years, and is more common in men. It is mainly manifested by progressive asymmetric limb weakness, mainly distal involvement, and may have mild sensory disturbances, often accompanied by muscle atrophy, muscle atrophy and muscle weakness. Non-parallel, prominent limb motor dysfunction, upper and lower limbs can be affected, upper limbs are heavier than lower limbs, distal ends are heavier than proximal ends. A small number of patients may have transient shoulder pain and mild paresthesia, but without certain and constant sensory disturbances.

Multifocal motor neuropathy

Laboratory inspection

Serum phosphokinase was mildly or moderately elevated, and high titers of anti-GM1 antibodies were positive in cerebrospinal fluid.

2. Peripheral nerve biopsy

It is an important laboratory test for differential diagnosis of peripheral neuropathy.

3. Neuromuscular electrophysiological examination

Shows its characteristic changes are continuous, multifocal, and partial motor conduction block. The latter refers to the selection of two points at the proximal and distal ends of the limb to stimulate the motor nerve, respectively, and the compound muscle action potential produced by the The amplitude and area are reduced, and the decrease is more than 20%, sometimes as high as 70% or more, without an abnormal transient dispersed phase. Conduction block can occur in multiple peripheral nerves or different segments of the same nerve at the same time. Conduction block is easily detected in the ulnar nerve, median nerve, and radial nerve.

Diagnosis of multifocal motor neuropathy

1. Core standards (both must be met at the same time)

(1) Local asymmetric limb weakness with slow or step-like progression, that is, at least two motor innervation areas are involved, and the symptoms persist for more than 6 months. If the symptoms and signs are only seen in one innervation area, only Diagnosed as possible MMN;

(2) No objective sensory disturbance, except for slight vibration abnormalities in the lower limbs.

Clinical support standards: mainly involving the upper limbs; weakened or disappeared tendon reflexes; the cranial nerves are not involved; painful spasms and beam tremors can be seen in the affected limbs; immunosuppressants can improve dysfunction and muscle strength

Exclusion criteria: signs of upper motor neurons; clear globular involvement; severe sensory disturbances; diffuse symmetry weakness in the first few weeks.

2. Electrophysiological standards

Confirmed motor block:

(1) Regardless of the length of the nerve (median, ulnar, and peroneal) segments, the negative area of the compound muscle action potential (CMAP) at the proximal end is reduced by 50% compared to the distal end. When stimulating the distal part of a segment with motion conduction block, the negative peak amplitude of CMAP must be> 20% of the normal lower limit and> 1mV, and the increase of the negative peak time limit of CMAP must be 30% compared with the distal end.

(2) Probable motor conduction block: CMAP negative peak time span of upper limbs spanning long segments (such as wrist to elbow or elbow to axillary) decreases by 30% at the proximal end compared to the distal end, and the area of negative CMAP peaks decreases 30%; or CMAP negative peak time span of upper limbs spanning long segments (such as wrist to elbow or elbow to axilla) when the proximal end is increased by> 30% compared to the distal end, the CMAP negative peak area is reduced by 50%.

(3) Sensory conduction examination of upper limb nerve segments with conduction block was normal.

Differential diagnosis of multifocal motor neuropathy

Should be distinguished from chronic Guillain-Barre syndrome (CIDP), amyotrophic lateral sclerosis (ALS or SMA) and other diseases.

Multifocal motor neuropathy treatment

This disease is a treatable disease. High-dose cyclophosphamide shock treatment, followed by oral administration of maintenance dose, improved clinical symptoms in most patients, and serum GM1 antibody titer decreased significantly. Large-dose immunoglobulins also have a good effect in treating MMN.

Prognosis of multifocal motor neuropathy

The prognosis is relatively good. Most patients develop slowly, and some patients often fail to take care of themselves due to muscle weakness. There can be different platforms and spontaneous remission periods.