The multifocal motor neuropathy (MMN) is a slowly progressing disease of the motor nerves that leads to various failures. Sensitive and vegetative nerves are not involved. An autoimmune process is assumed to be the cause.
What is multifocal motor neuropathy?MMN is characterized by the occurrence of asymmetrical distal paresis of the upper extremities, which, however, can lead to muscle atrophy only after a long time.
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The multifocal motor neuropathy is characterized by the slow failure of motor nerves. During examinations, antibodies against the ganglioside GM1 are detected. It is therefore an autoimmune disease. The neuropathy is assigned to the Guillain-Barré syndrome. The Guillain-Barré syndrome is a collective term for autoimmune diseases of the nervous system that impair muscle function.
Multifocal motor neuropathy is characterized by functional disorders of the ulnar nerve and the median nerve. It is a very rare condition with a prevalence of 1 to 2 per 100,000 people. Neuropathy usually occurs for the first time between the ages of 30 and 50. Men are two to three times more likely to have multifocal motor neuropathy than women. Symptoms also appear much earlier in men.
MMN has symptoms similar to ALS and must always be differentiated from it in a differential diagnosis. In contrast to ALS, however, there are good treatment options that can stop the progression of the disease and even reverse it.
The possible cause of the multifocal motor neuropathy is an autoimmunological process in which autoantibodies against the ganglioside GM1 are formed. As sphingolipids, gangliosides are part of cell membranes. They play a role in making cell contacts. They are also responsible for the immune system's recognition of nerve cells.
If these phospholipids fail, the nerve signals are only transmitted weakly. Nerve failures up to pareses can occur. The autoantibodies bind to the gangliosides and thereby switch them off. Therefore, the transmission of excitation is inhibited locally and muscle performance is impaired. In the case of multifocal motor neuropathy, the ulnar nerve and the median nerve are affected.
Symptoms, ailments and signs
MMN is characterized by the occurrence of asymmetrical distal paresis of the upper extremities, which, however, can lead to muscle atrophy only after a long time. Sometimes there is no atrophy at all or they are poorly developed. As mentioned earlier, the ulnar and median nerves are mainly affected.
The ulnar nerve is a motor nerve of the arm. He is responsible for the forearm muscles and hands. The median nerve also innervates muscles of the forearm and the hands or fingers. In rare cases, involvement of the cranial nerves is also possible. In addition, muscle cramps and involuntary movements of small muscle groups occur (fasciculations). In very rare cases, respiratory paralysis is also possible due to the involvement of the diaphragmatic nerves.
The muscle reflexes decrease in the course of the disease. However, there are hardly any sensitivity disorders. However, if the phrenic nerve is involved, respiratory problems can occur. However, this only happens in about one percent of cases. Sometimes the lower extremities are also affected by multifocal motor neuropathy. However, this is only very rarely the case.
Particularly at the beginning of the disease, the discrepancy between the often considerable paresis and the only insignificant muscle atrophy is noticeable. However, as the disease progresses, the atrophies become more pronounced due to the gradual destruction of the myelin sheaths.
Diagnosis and course of disease
Multifocal motor neuropathy is characterized by almost identical symptoms to amyotrophic lateral sclerosis (ALS), so that it is difficult to distinguish the two diseases. The same applies to spinal muscular atrophy and nerve compression syndrome. A differential diagnosis must be performed to rule out these disorders.
Blood analyzes, brain water examinations and imaging procedures do not lead to any result. A typical indication of multifocal motor neuropathy is the appearance of nerve conduction blocks in the motor electroneurographs. The sum of the total muscle potentials of the proximal nerve stimulations is significantly more than 50 percent reduced compared to the total muscle potentials of the distal nerve stimulations.
An additional electromyography performed shows a reduction in the proportion of nerves in the skeletal muscles. The GM1 antibody can also be determined. If the titer of this autoantibody is increased, there is another indication of MMN.
As a result of this disease, those affected usually suffer from various motor deficits. As a result, the patient's everyday life is usually made significantly more difficult and the quality of life is also greatly reduced and restricted. The patients primarily suffer from severe muscle pain and can no longer move them at will.
Cramps and epileptic fits, which are associated with severe pain, can also occur. In the worst case, this also paralyzes breathing, so that the person concerned is undersupplied with air and possibly also loses consciousness. This can lead to injury if you fall.
As a result of the disease, patients also suffer from disorders of sensitivity or paralysis all over their bodies. These can also significantly restrict everyday life, so that those affected need the help of other people in their lives. Self-healing does not usually occur with this disease.
Treatment of this disease can be carried out with the help of drugs. However, those affected are usually also dependent on various therapies that maintain the functions of the muscles. As a rule, there are no particular complications.
When should you go to the doctor?
Multifocal motor neuropathy should be clarified by a doctor if classic symptoms such as muscle cramps or involuntary movements occur. Sensitivity disorders and respiratory problems indicate an advanced disease that needs to be diagnosed and treated immediately. The disease can be recognized at the beginning by the irregular alternation between slight muscle cramps and severe paresis. People who notice the symptoms mentioned should ideally see their family doctor directly.
The doctor can make an initial suspected diagnosis and consult a specialist if necessary. In the event of motor failures, the emergency doctor must be called. The same applies to convulsions, epileptic seizures and respiratory paralysis. In the event of a fall due to an attack, first aid must also be provided. The person concerned is then cared for in the hospital. The actual treatment is carried out by a neurologist or another specialist in internal diseases. The treatment also includes extensive physiotherapy, which tries to preserve the mobility of the limbs.
Therapy and Treatment
In contrast to amyotrophic lateral sclerosis, multifocal motor neuropathy can be treated well. A differential diagnosis is therefore very important to differentiate between the two diseases. For example, some patients with the previous diagnosis of ALS are diagnosed with MMN on closer examination. The MMN can be treated well with immunoglobulins.
It was found that 40 to 60 percent of all patients diagnosed with MMN were able to prevent their disease from progressing through this treatment. The earlier the therapy is started, the more favorable the prognosis. Therapy is usually carried out for six years. During this time the dose of immunoglobulins is increased from an initial twelve to seventeen grams per week.
Side effects of this treatment are not known. However, since irreversible damage to the nerve cells occurs in the course of the disease, the success of the therapy depends on the time at which the therapy is started.
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Outlook & forecast
The prospects for multifocal motor neuropathy are generally poor. Many scientists emphasize that the administration of immunoglobulins prevents the disease from progressing. However, according to statistical studies, this helps a maximum of sixty percent of those affected. The others suffer from permanent muscle weakness and have to accept restrictions in their lives. Another disadvantage is that the long-term administration of immunoglobulins is usually ineffective. Then permanent deficits develop. The risk of developing multifocal motor neuropathy is greatest between the ages of 30 and 50. From a statistical point of view, men in particular are considered vulnerable.
In the best-case scenario, the symptoms regress. Doctors particularly hope that the treatment will be successful if the symptoms have not progressed too far. Starting therapy at an early stage can therefore be regarded as ideal. Multifocal motor neuropathy mainly affects the extremities. The disease rarely spreads to the cranial and diaphragmatic nerves, which leads to further complications. Disabilities and weaknesses arise especially and demonstrably when the multifocal motor neuropathy has remained untreated for a long time.
It is not known what options there are to prevent multifocal motor neuropathy, because the cause of this disease is unclear. It is an autoimmune disease. However, when the first symptoms appear, treatment should begin quickly, because the success of the therapy depends largely on the time at which the therapy is started.
Follow-up care for multifocal motor neuropathy depends on the course of the disease. If treatment with immunoglobulins is started early, there is even a good chance of a complete cure in some cases.However, if therapy is started later, the chances of complete resolution of the disease worsen.
Then often only attempts can be made to counteract a worsening of the symptoms. In any case, it is a lengthy therapy, which must be accompanied by intensive aftercare measures. Treatment with immunoglobulins is usually repeated every four to eight months. Afterwards, detailed examinations should always be carried out in order to document the progress of the therapy.
The administration of immunoglobulins leads to at least a stop in the progression of the disease in around 40 to 60 percent of cases. However, if the follow-up examinations show resistance to therapy, an attempt can be made to improve the symptoms with the aid of other active ingredients such as cyclophosphamide in combination with immunoglobulins.
Particularly in the case of an unfavorable prognosis with increasing inability to move, psychological therapy must often be integrated into the follow-up measures because, despite normal life expectancy, the quality of life is considerably restricted. At the same time, aftercare also includes the procurement of suitable aids, which are necessary if the mobility of the lower extremities is significantly impaired.
You can do that yourself
If you start physical activity immediately after the diagnosis, you cannot influence the course of the disease, but it helps to maintain muscle strength and movement. If necessary, it is important to use joint supports or bandages to prevent overloading certain muscle groups.
If problems arise at work due to illness, the integration department offers comprehensive help. The employees advise and are helpful in communicating with the employer and applying for aids to maintain the workforce.
If the disease is very advanced, it is hardly possible to live independently without outside help. In this case, it is important to apply for a care level at an early stage, on the one hand to financially support the caring relatives or on the other hand to receive external part-time care. Each patient and their family have to decide which path is the right one. It is often less psychologically stressful to get help from outside. The step to a therapist should not be avoided either, as an emotional imbalance can also lead to physical complaints.
If there is a complete need for help in all situations, external support around the clock can also be requested. With this support, those affected are sometimes even able to return to their job and take part in social life.