Myotonia congenita Becker belongs to the general group of so-called myopathies (muscle diseases). It is characterized by delayed establishment of the resting membrane potential after a muscle contraction. That is, muscle tone decreases only slowly.
What is myotonia congenita Becker?
Myotonia congenita Becker is a muscle disorder (myopathy) that belongs to the special group of myotonia. Myotonia is characterized by prolonged increased muscle tone. Thus, the muscle relaxes only slowly after a muscle contraction. Myotonia is a disorder of the sodium ion channel. The resting potential between potassium ions inside the cell and sodium ions outside the cell is restored only slowly during excitation. In terms of muscle tension (muscle tone), this means the prolonged maintenance of a certain change caused by muscle force. For example, when the patient clenches his fist, it takes a while before he can open it again. Myotonies are usually genetically determined. They involve defects in enzymes responsible for chloride ion transport in the sodium channel. Myotonia congenita Becker is also characterized by identical symptoms to myotonia congenita Thomsen, as both disorders affect chloride ion transport. With a prevalence of 1 in 25,000, myotonia congenita Becker is a very rare muscle disorder. However, the prognosis is very good. No restriction of life expectancy is observed.
Causes
The cause of myotonia congenita Becker is described as a genetic defect in the CLCN1 gene on chromosome 7. This gene is responsible for the formation of an enzyme that regulates the transport of chloride ions through the sodium channel. Due to this enzyme defect, chloride ions cannot be transported as well, and the resting potential of the cell membrane is established only slowly. The resting membrane potential is an actively generated cell potential, which is formed between the interior of the cell and the intercellular space. Potassium ions are constantly pumped into the cell and sodium ions out of the cell by the so-called sodium-potassium ion pump. Thus, the potassium ion concentration is increased inside the cell and decreased outside. The reverse, of course, is also true for sodium ions. The resulting potential is actively maintained in order to be able to transmit electrical impulses via potential changes. Normally, when the potential is reversed by this impulse, the initial state is quickly restored. However, this process is delayed in myotonia congenita Becker due to impaired chloride ion transport. The same is true for myotonia congenita Thomsen. Both diseases are caused by defects of the same gene. However, different mutations are present here. While myotonia congenita Thomsen is inherited in an autosomal dominant manner, myotonia congenita Becker follows an autosomal recessive mode of inheritance.
Symptoms, complaints, and signs
The leading symptom of myotonia congenita Becker is prolonged muscle tension (muscle tone). The muscle does not relax immediately, as is normal for a normal muscle response, but rather with a delay. Posture triggered by voluntary muscle contraction is maintained longer. The delayed opening of the fist when the patient clenches his fist has already been mentioned. Furthermore, after prolonged physical rest, standing up and walking is initially possible only with difficulty. After a so-called warm-up phase, movements return to normal. Muscle stiffness is particularly pronounced in cold outdoor temperatures or when staying in cold water. When tapping the skeletal muscles, a tonic contraction occurs, which is also called percussion myotonia. Patients fall more often and appear clumsy when grasping objects. However, muscle development is normal. Even an athletic physique is possible because myotonia is not associated with muscle weakness. However, muscle weakness may occur with prolonged physical rest.
Diagnosis and course of the disease
When diagnosing myotonia congenita Becker, a medical history is first taken. Physical examinations such as tapping the skeletal muscles to produce percussion myotonia and electromyography follow.Electromyography reveals discharge series suggestive of myotonia. Now the differential diagnosis to myotonia congenita Thomsen is made. Both diseases are very difficult to distinguish. The heredity of the myotonia can be determined during the anamnesis. If an autosomal recessive mode of inheritance is indicated, myotonia congenita Becker can be diagnosed. However, only genetic testing can provide an exact answer.
Complications
Myotonia congenita Becker causes significant limitations and complications in the patient, especially in everyday life. In most cases, the muscles cannot relax immediately, so certain activities cannot be performed by the patient. Likewise, standing up can become a difficulty if the affected person has previously rested and the muscles have not been active. Myotonia congenita Becker significantly reduces the quality of life. Affected individuals also suffer from severe stiffness of the muscles, which also has a negative effect on the patient’s posture. It is not uncommon for those affected to appear clumsy and be unable, for example, to grasp or lift objects properly. This leads to severe limitations in everyday life and, in children, to extreme developmental delay. Muscle weakness can also occur, so that the resilience of the affected person decreases significantly. A direct treatment of Myotonia congenita Becker is not possible. However, those affected are dependent on various therapies that can significantly alleviate the symptoms. As a rule, no complications occur. In some cases, however, the heart muscle is also affected, so patients may be dependent on medications to prevent cardiac symptoms.
When should you see a doctor?
If muscle tension cannot be released despite a consciously initiated relaxation, a doctor is needed. A delayed muscle response is considered unusual and should be presented to a physician. Stiff posture, problems with grip function, and disturbances in general movement should be discussed with a physician. If there are frequent falls or accidents due to the complaints, a medical clarification of the cause is necessary. A treatment plan must be drawn up so that relief of the symptoms can be initiated. If there is a general severity after a period of rest, restrictions in locomotion after a break or gait unsteadiness, the affected person needs help and support. A physician is needed to determine the disorders present. A decrease in physical ability, difficulty in meeting daily responsibilities, and an inability to perform usual athletic activities must be discussed with a physician. There is a medical condition that needs to be treated. If the complaints persist unabated for several days or if there is an increase in the disturbances, a doctor should be consulted. If the affected person appears clumsy in everyday life, displays behavioral problems or experiences emotional problems, a doctor should be consulted. The physical impairments increase the risk of a secondary mental illness.
Treatment and therapy
Patients with myotonia congenita Becker do not require treatment in most cases. With some training, they can learn to perfect their movements to compensate for symptoms. In severe cases, however, drug treatment is sometimes necessary. This involves giving mexiletine, which is known as an antiarrhythmic drug for cardiac arrhythmias. This drug blocks the sodium channel. Acetazolamide, carbamazepine or diazepam can also be used. However, drug treatment should be short term because it can have various side effects. However, especially if muscle stiffness has occurred as a result of exposure to cold, drug treatment may be useful.
Outlook and prognosis
Myotonia congenita Becker carries a differential prognosis. A cure is impossible because it is a hereditary disease. Physicians can only relieve the symptoms. Often, no prolonged treatment is necessary because the symptoms are minimal. In such a course, patients receive information on how to compensate for the signs in everyday life. Training sessions are usually guided by physiotherapists.These measures are sufficient to prevent restrictions in the quality of life. In the case of a severe course, medication is indicated. The active substances available provide temporary relief of the condition. However, side effects sometimes occur while taking the medication. Stiff muscles very often occur in everyday life. Clumsiness and awkward posture are also characteristic. The ability to cope with stress in professional and private life is significantly reduced. Myotonia congenita Becker does not lead to a shortened lifespan. According to statistical surveys, the disease occurs in one patient out of 25,000 people. Many affected individuals receive myotonia congenita Becker through their parents by inheritance. The symptomatic state usually remains at a similar level. Changes are very rare and occur insidiously.
Prevention
Myotonia congenita Becker is a genetic disorder, so there is no possibility of prophylaxis. However, the onset of symptoms can be prevented. It is important to avoid cold weather in particular. This also applies to bathing in cold water. This is because the muscles stiffen very quickly. Furthermore, continuous movement is necessary to counteract the stiffening of the muscles. It is also possible to compensate for the symptoms of myotonia congenita Becker through exercise training.
Follow-up
In most cases of myotonia congenita Becker, affected individuals have only a few and also limited measures of aftercare available to them. For this reason, affected individuals should see a physician at an early stage to prevent the occurrence of other complications or symptoms. It is not possible for patients to heal on their own, so they are dependent on the help of a doctor. Follow-up care often includes physical therapy or physiotherapy in order to alleviate the discomfort permanently and properly. Here, many of the exercises from such therapies can also be repeated in the patient’s own home to speed healing. Often, in the case of Myotonia congenita Becker, the help and care of one’s own family is also very important. When taking medication, care must be taken to ensure that the correct dosage is given and that it is taken regularly in order to counteract the symptoms. Affected persons should always consult a doctor first if they are unclear or have any questions. Myotonia congenita Becker does not usually reduce the patient’s life expectancy. Frequently, contact with other affected persons is also very useful, as this can lead to an exchange of information.
What you can do yourself
Becker’s myotonia congenita can be treated by patients themselves through some self-help measures and various household and natural remedies. Various exercises from physiotherapy make it easier to get up and walk in the morning. Thus, by repeating the movement, the so-called “warm-up phenomenon” can be achieved, in which the movements can be performed increasingly easier and with less pain. In cold outdoor temperatures, the patient should wear warm clothing, as muscle stiffness is particularly pronounced under these conditions. If medication has been prescribed for the condition, the use of alternative remedies should be discussed with the physician beforehand. The physician can give tips for an adapted diet, through which the typical muscle complaints can often be reduced. Since there is an increased risk of accidents in myotonia congenita Becker, the patient should not be left alone. In the event of a fall, it is important to call the emergency physician and provide first aid to the affected person. If accidents occur repeatedly, adaptations must be made in the home, such as support handles or grab bars. In the advanced stage, the patient is dependent on a wheelchair.
