Multifocal motor neuropathy (MMN) is a slowly progressive disease of motor nerves that results in various deficits. Sensory and autonomic nerves are not involved. The cause is thought to be an autoimmunologic process.
What is multifocal motor neuropathy?
Multifocal motor neuropathy is characterized by the slow loss of motor nerves. On examination, antibodies to ganglioside GM1 are detected. Thus, it is an autoimmune disease. The neuropathy is classified as Guillain-Barré syndrome. Guillain-Barré syndrome is a collective term for autoimmune diseases of the nervous system that affect muscle function. Multifocal motor neuropathy is characterized by dysfunction of the ulnar and median nerves. It is a very rare condition with a prevalence of 1 to 2 per 100,000 people. Most often, neuropathy first appears between the ages of 30 and 50. Men are two to three times more likely to be affected by multifocal motor neuropathy than women. Symptoms also appear much earlier in men. MMN has similar symptoms to ALS and must always be differentiated from it by differential diagnosis. However, unlike ALS, good treatment options exist that can halt and even reverse disease progression.
Causes
The cause of multifocal motor neuropathy may be an autoimmunologic process involving the production of autoantibodies against ganglioside GM1. Gangliosides, as sphingolipids, are a component of cell membranes. They play a role in the establishment of cell contacts. They are also responsible for the recognition of nerve cells by the immune system. If these phospholipids fail, nerve signals are only weakly transmitted. This can lead to nerve failures and even paresis. The autoantibodies bind to the gangliosides and thus switch them off. Therefore, excitation transmission is locally inhibited and muscle performance is impaired. In the case of multifocal motor neuropathy, the ulnar and median nerves are affected.
Symptoms, complaints, and signs
MMN is characterized by the occurrence of asymmetric distal paresis of the upper extremities, although this may take a long time to lead to muscle atrophy. At times, there are no atrophies at all or they are mild. As mentioned above, the ulnar and median nerves are mainly affected. The ulnar nerve is a motor nerve of the arm. It is responsible for the forearm muscles and the 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. Furthermore, muscle spasms and involuntary movements of small muscle groups (fasciculations) occur. In very rare cases, respiratory paralysis is also possible due to involvement of the phrenic nerves. Muscle reflexes decrease in the course of the disease. However, sensory disturbances rarely occur. However, respiratory problems may occur if the phrenic nerve is involved. However, this occurs in only about one percent of cases. Sometimes the lower extremities are also affected by multifocal motor neuropathy. However, this is also very rarely the case. Especially at the beginning of the disease, the discrepancy between the often considerable pareses and the only insignificant appearing muscle atrophies is striking. However, as the disease progresses, the atrophies become more prominent due to the gradual destruction of the myelin sheaths.
Diagnosis and course of the disease
Multifocal motor neuropathy is characterized by almost identical symptoms to amyotrophic lateral sclerosis (ALS), making the two diseases difficult to distinguish. The same is true for spinal muscular atrophy and nerve compression syndrome. Differential diagnosis must be performed to rule out these disorders. Blood analyses, cerebrospinal fluid tests, and imaging techniques do not lead to any results in this case. A typical indication of multifocal motor neuropathy is the appearance of nerve conduction blocks in the motor electroneurographs.Here, the sum of the muscle sum potentials of the proximal nerve stimulations is significantly reduced by more than 50 percent compared to the muscle sum potentials of the distal nerve stimulations. An additionally performed electromyography shows a reduction of the nerve content in the skeletal muscles. GM1 antibody can also be determined. If the titer of this autoantibody is elevated, there is further evidence of MMN.
Complications
Due to this disease, in most cases, affected individuals suffer from various motor deficits. As a result, the patient’s daily life is usually made much more difficult and the quality of life is equally reduced and limited. Patients primarily suffer from severe muscle pain and are no longer able to move them voluntarily. Cramps and epileptic seizures can also occur, which are associated with severe pain. In the worst case, this also paralyzes breathing, so that the affected person is undersupplied with air and possibly also loses consciousness. In the process, an injury may possibly occur in the event of a fall. Throughout the body, patients also suffer from sensory disturbances or paralysis as a result of the disease. These can also significantly limit everyday life, so that those affected need the help of other people in their lives. Self-cure does not usually occur with this disease. Treatment of this disease can be carried out with the help of medication. However, sufferers are also usually dependent on various therapies to maintain the functions of the muscles. Particular complications usually do not occur.
When should you see a doctor?
Multifocal motor neuropathy should be evaluated by a physician if classic symptoms such as muscle spasms or involuntary movements occur. Sensory disturbances and respiratory problems indicate that the disease is already advanced and should be diagnosed and treated promptly. The disease can be recognized at the beginning by the irregular alternation between mild muscle spasms and severe paresis. People who notice the aforementioned symptom pattern in themselves should ideally visit their family doctor directly. The physician can make an initial tentative diagnosis and, if necessary, consult a specialist. In the event of motor deficits, the emergency physician must be called. The same applies to convulsions, epileptic seizures and paralysis of breathing. If a fall occurs due to a seizure, first aid must also be administered. The affected person is then cared for in the hospital. The actual treatment is provided by a neurologist or other specialist in internal diseases. Part of the treatment also includes extensive physical therapy, which attempts to preserve the limbs’ ability to move.
Treatment and therapy
Unlike amyotrophic lateral sclerosis, multifocal motor neuropathy can be well treated. Therefore, differential diagnosis is very important to distinguish the two diseases. For example, some patients with a prior diagnosis of ALS are diagnosed with MMN upon closer examination. MMN can be well treated with immunoglobulins. It has been found that in 40 to 60 percent of all patients diagnosed with MMN, progression of the disease could be prevented by this treatment. The prognosis is more favorable the earlier the therapy is started. The therapy is usually administered 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, because irreversible damage to nerve cells occurs during the course of the disease, the success of therapy depends on when therapy is started.
Outlook and prognosis
The outlook for multifocal motor neuropathy is basically poor. Although many scientists emphasize that administration of immunoglobulins prevents disease progression. However, according to statistical studies, this helps a maximum of sixty percent of those affected. The others suffer permanently from muscle weakness and have to accept restrictions in their lives. Another disadvantage is that long-term administration of immunoglobulins is usually ineffective. Permanent deficits then develop. The risk of developing multifocal motor neuropathy is greatest between the ages of 30 and 50.Statistically, men in particular are considered susceptible. In the best case, the symptoms regress. Doctors are particularly hopeful of successful treatment if the symptoms have not yet progressed too far. Therefore, starting therapy at an early stage can be considered ideal. Multifocal motor neuropathy mainly affects the extremities. Rarely, the disease extends to the cranial and phrenic nerves, resulting in further complications. Disabilities and weaknesses develop especially and demonstrably when multifocal motor neuropathy has been left untreated for a long time.
Prevention
What options there are for preventing multifocal motor neuropathy is not known, because the cause of this condition is unclear. It is an autoimmune disease. However, when the first symptoms appear, treatment should be started quickly, because the success of therapy depends largely on when therapy is started.
Follow-up care
Follow-up care for multifocal motor neuropathy depends on the particular course of the disease. If treatment with immunoglobulins is started early, there is even a good chance of complete recovery in some cases. However, if therapy is started later, the prospects of complete regression of the disease worsen. Then often only attempts can be made to counteract a worsening of the symptoms. In any case, this is a protracted therapy, which must be accompanied by intensive follow-up measures. Treatment with immunoglobulins is usually repeated every four to eight months. Thereafter, detailed examinations should always be performed to document the progress of the therapy. The administration of immunoglobulins leads in about 40 to 60 percent of cases at least to a halt in the progression of the disease. However, if resistance to therapy becomes apparent in the follow-up examinations, an attempt can be made to bring about an improvement in the symptoms with the aid of other agents such as cyclophosphamide in combination with immunoglobulins. Particularly in the case of an unfavorable prognosis with increasing immobility, psychological therapy must often be integrated into the aftercare measures because, despite a normal life expectancy, the quality of life is considerably reduced. At the same time, aftercare also includes the procurement of appropriate assistive devices, which become necessary when the ability to move the lower extremities is significantly impaired.
What you can do yourself
If you start physical activity immediately after diagnosis, you cannot influence the course of the disease, but you will favor the preservation of muscle strength and movement. It is important to use joint supports or bandages when necessary to prevent overuse of certain muscle groups. If problems arise at work due to illness, the Integration Office offers comprehensive help. The employees advise and assist in communicating with the employer and in applying for aids to maintain the working capacity. In the case of a severely advanced disease, independent living without outside help is hardly possible. In this case, it is important to apply for a care level at an early stage in order to support the caring relatives financially on the one hand or to obtain external part-time care on the other. Which path is the right one must be decided by each patient together with his or her family. Often it is psychologically less stressful to get help from the outside. Also the step to the therapist may not be shied away, since a mental imbalance can lead also to physical complaints. If there is a complete need for help in all areas of life, external support around the clock can also be requested. With this support, it is sometimes even possible for those affected to return to their jobs and participate in social life.
