Multifocal motor neuropathy
Multifocal motor neuropathy (MMN) - a rare autoimmune disease characterized by progressive asymmetric weakness without impaired sensitivity.
The disease is rare, with a worldwide prevalence of less than 1 case per 100,000 people. It occurs 2.7 times more often in men than in women. MMN is usually diagnosed in adults between the ages of 30 and 50, although it also occurs in other age groups.
As a rule, MMN progresses slowly, which leads to asymmetric weakness, more often in the upper extremities. In this connection, at the beginning of the disease, patients notice difficulties in writing, unscrewing bottle caps and impaired fine motor skills. At the same time, patients have no complaints of impaired sensitivity (no numbness, tingling, pain). There may also be complaints of muscle twitching.
Mechanisms of disease development
MMH is an autoimmune disease in which one's own immune system attacks the nodal zones of the motor nerves – the areas of nerve fibers that provide the transmission of nerve impulses. Patients have specific antibodies to GM1, ganglioside or sugar-containing lipid found in peripheral nerves. As a result of the action of antibodies against the nodal regions of the peripheral nerves, a block of excitation along the motor nerve develops, which leads to a violation of impulse transmission to the muscle.
Based on complaints, medical history and assessment of neurological status, a neurologist determines indications for the following research methods:
- Stimulation electroneuromyography (ENMG). The method using cutaneous electrodes makes it possible to evaluate the conductivity of impulses along the nerves in response to their stimulation by electric current. In patients with MMN, this method makes it possible to detect conduction blocks along the motor fibers of peripheral nerves. In this case, the conductivity along the sensory fibers will not be impaired. Needle electromyography (iEMG) is also prescribed for differential diagnosis.
- Ultrasound examination of peripheral nerves allows to establish a change in the structure of the nerve and an increase in the cross-sectional area.
- MRI of the brachial plexuses with contrast allows you to determine the asymmetric signal amplification in patients with this disease.
- A blood test for the presence of antibodies to GM1.
- Lumbar puncture (spinal puncture). During the puncture, cerebrospinal fluid (cerebrospinal fluid) is taken from the spinal canal to assess the amount of protein and the presence of protein-cell dissociation, which may be required for differential diagnosis.
The main variant of proven pharmacological treatment of MMH is intravenous immunoglobulin (IVIG). The drug is approved by the Federal Drug Administration (FDA). Three-quarters of patients have positive dynamics in the form of increased muscle strength, however, the effect is short-lived, and only 20% of patients achieve long-term remission. Most patients need periodic injections of IVIG.
In the absence of the effect of IVIG, it is possible to consider immunomodulatory agents such as cyclophosphamide, mycophenolate mofetil, azathioprine and rituximab. However, from the standpoint of evidence-based medicine, numerous comparative randomized controlled trials are required to confirm the effectiveness of this therapy in patients with MMN. Glucocorticosteroids and plasmapheresis are known to be ineffective in patients with MMN.
To consult a neurologist, conduct electromyography and prescribe therapy, you can contact the Center for Neuromuscular Pathology MCSC named after A.S. Loginov.
Conducting a comprehensive examination and receiving pathogenetic treatment is possible during hospitalization in the neurological department of the MCSC named after A.S. Loginov.
Make an appointment for a consultation at the Central Medical Center : +7 (495) 304-30-39