What Is Multifocal Motor Neuropathy?
Multifocal motor neuropathy is a chronic progressive peripheral neuropathy related to immune-mediated, mainly involving the motor nerve terminal.
Patients with this disease may present with chronic onset and progressive distal limb weakness, mainly in the upper limbs. The involvement of the bilateral limbs is not symmetrical, but the sensory nerves are mostly unaffected. Therefore, patients will not have numbness, loss of sensation, paresthesia and other symptoms. Motor block could be detected by EMG, and GM1 antibody to ganglioside could be found in plasma of most patients.
Immunotherapy for this disease is effective, and the prognosis is usually good.
Is multifocal motor neuropathy common?
Multifocal motor neuropathy is rare, with an estimated prevalence of 0.6 to 2 per 100,000.
What Causes Multifocal Motor Neuropathy?
The etiology and pathogenesis of multifocal motor neuropathy are not completely clear.
The possible mechanism discovered at present is that some infectious factors (such as Campylobacter jejuni) have similar structures to the glycosphingolipid antigenic determinants of motor nerve endings in the body. When the body's immune system produces protective antibodies against foreign antigens, "mistakenly" takes its normal glycosphingolipids as "foreign antigens" to produce ganglioside GM1 antibody, which can bind to the nerve surface to affect the normal function of the nerve and damage the peripheral nerves. The motor nerve endings are the most vulnerable, so the limb motor symptoms are the most obvious.
What Are The Symptoms Of Multifocal Motor Neuropathy?
Patients with multifocal motor neuropathy usually start at the age of 20–50, with an average age of 30–40. It is more common in men. The onset of the disease is insidious and symptoms mostly progress slowly.
Patients with this disease often present with progressively worsening muscle weakness and muscle atrophy at the distal end of the limbs, mainly in the upper limbs, often onset from hand muscles, manifested as sagging wrists, unstable holdings, and hand muscle atrophy. The symptoms gradually developed for the forearm and upper arm, and there was weakness in raising the arm, and even unable to complete daily activities such as dressing and combing.
Symptoms gradually affect the muscles of the lower limbs, and can gradually affect activities such as running, climbing, squatting, and walking. In a few cases, the respiratory muscles can also be affected, which affects the respiratory function, causing breathing effort, depression, and even respiratory failure. The degree of involvement of the bilateral limbs is not symmetrical, and different muscle groups of the same limb can also be distributed asymmetrically.
Some patients may also develop fasciculation and painful spasm, that is, the sensation of "muscle jump" or "cramp". Patients usually have no paresthesia or sensory disturbances, and in a few cases they may have a slight paresthesia. Meanwhile, cranial nerves and medullary muscles are usually not involved in patients with multifocal motor neuropathy.
What are the serious consequences of multifocal motor neuropathy?
Multifocal motor neuropathy mainly affects patients' motor function, and can seriously impair patients' ability of daily living in the later stage of the disease. In addition, in a few cases, respiratory muscles can also be involved, and patients suffer from severe conditions such as breathing difficulty, suffocation, and even respiratory failure.
How Is Multifocal Motor Neuropathy Diagnosed?
According to the diagnostic criteria for multifocal motor neuropathy proposed by the European Society of Neurology/Peripheral Neurology in 2010, the diagnosis of the disease must meet the following core criteria:
- Focal asymmetric limb weakness with chronic progression.
- The affected motor nerves were distributed to at least two different nerves, and the symptoms lasted for more than one month.
- There were no sensory symptoms or only minor lower extremity tremor abnormalities.
There are also the following clinical support standards:
- The main upper limb was involved, the tendon reflex of the involved limb was weakened or disappeared, no cranial nerve was involved, and the involved limb showed fasciculation and clonus.
- Immunomodulatory treatment is effective.
Including upper motor neuron signs, bulbar paralysis caused by medulla oblongata involvement, obvious sensory abnormality, and extensive symmetrical myasthenia at the early stage of symptoms.
According to the diagnostic criteria, combined with auxiliary examinations, including typical focal motor nerve block shown in EMG and detection of GM1 antibody in serum, the disease could be diagnosed after other similar diseases were excluded.
What conditions need to be differentiated from multifocal motor neuropathy?
Multifocal motor neuropathy needs to be differentiated from other diseases that cause distal weakness of both limbs, mainly including motor neuron disease, other chronic multiple peripheral neuropathy, muscle diseases, etc.
Can Multifocal Motor Neuropathy Be Prevented?
The pathogenesis of this disease is ominous, so there is no special prevention method. Avoiding cold, infection, etc. may help reduce the incidence.
How can patients with multifocal motor neuropathy prevent other diseases caused by it?
Enhancing care for patients and their caregivers can minimize accidents such as falls, and timely treatment can help reduce complications such as respiratory paralysis.
How Is Multifocal Motor Neuropathy Treated?
The treatment of multifocal motor neuropathy is relatively limited, mainly including immunotherapy and nutritional nerve therapy, of which immunotherapy is the main one.
Can multifocal motor neuropathy be cured by itself?
Does multifocal motor neuropathy need to be hospitalized?
- Mainly include intravenous gamma globulin (IVIG). The mechanism of action of IVIG may be related to inhibiting antibody production and increasing antibody degradation. Symptoms of most patients can be improved after treatment, and some patients require repeated IVIG treatment.
- During IVIG treatment, it is necessary to pay attention to the adverse reactions related to the infusion of blood products (allergies, infusion reactions, etc.), as well as the risk of potential blood-borne infections.
- For patients with poor response to IVIG treatment or unable to continue infusion, the immunosuppressant cyclophosphamide may be considered. But be aware of the side effects of cyclophosphamide, which may cause hemorrhagic cystitis, amenorrhea, sperm reduction, bone marrow suppression, etc. The drug should be stopped immediately after these symptoms appear.
- Other immunomodulatory treatments, such as rituximab, are currently in the trial phase, and their efficacy remains to be seen. Hormones, plasma exchange, etc. are not recommended for patients with multifocal motor neuropathy.
Nutritional nerve therapy
It mainly includes vitamin B12 and vitamin B1, which may help the repair of peripheral nerves.
What is the prognosis of patients with multifocal motor neuropathy?
Patients with multifocal motor neuropathy usually have a good prognosis. Some patients may recover significantly, and some may have symptoms of muscle weakness. The length of the disease varies, most can live for decades, and a small number of patients with acute onset can die of respiratory failure within one year.
What Should Patients With Multifocal Motor Neuropathy Pay Attention To In Life?
Patients with multifocal motor neuropathy may affect their daily life due to muscle weakness, and family members need to strengthen their care to avoid accidents such as falls.
What should patients with multifocal motor neuropathy pay attention to in diet?
There are no special precautions, just keep healthy eating habits and appropriately increase the intake of vitamins such as vegetables and fruits.
Does multifocal motor neuropathy need to be reviewed?