Paramyotonia congenita belongs to the group of forms of myotonia characterized by prolonged states of muscle tension. It is a genetic disorder in which the function of sodium channels is impaired. Symptoms occur only when the muscles cool down or during prolonged physical activity and are not noticeable or barely noticeable when the muscles are warm.
What is paramyotonia congenita?
Paramyotonia congenita is a disorder of muscle function that manifests as prolonged tension after muscle contraction or exposure to cold. This disease was first described by the neurologist Albert Eulenberg, who lived from 1840 to 1917. For this reason, paramyotonia congenita is also known as Eulenberg’s disease. In contrast to the other myotonies such as Myotonia congenita Thomsen and Myotonia congenita Becker, it is not a chloride channel myotonia, but a sodium channel myotonia. In this case, there is a disturbance of the sodium ion transport. Sodium ions flow into the cell to generate the action potential. These are normally transported out of the cell again immediately after the muscle contraction until a membrane rest potential is formed. In paramyotonia congenita, this process is delayed and may take several hours. Mainly when exposed to cold or after prolonged muscle stress, muscle tension states can be poorly relieved. In contrast to chloride channel myotonia, the muscles stiffen even more during movement. Voluntary muscles are particularly affected by this disorder.
Causes
Point mutations on the SCN4A gene, which is located on chromosome 17, have been identified as the cause of paramyotonia congenita. As a result of these mutations, sodium channel function is severely impaired in muscle cells. Sodium ions flow into the cell to develop the action potential. However, in the resting potential state, the sodium ion concentration outside the cell is greater than inside. Thus, there is a higher potassium ion concentration than sodium ion concentration inside the cell. The resting potential is actively established by the ion pump function of the sodium channel. When the process of resting potential restoration from the action potential is disturbed, a long-sustained state of muscle tension occurs. This is referred to as myotonia because muscle tone remains elevated for a long time. In paramyotonia congenita, the influx of sodium ions into the cell is favored, especially during cold exposure and muscle contraction. Two causes for the build-up of a particularly high action potential are discussed. One part is probably due to the fact that the sodium channels are no longer closed. Another part of the sodium channel myotonia is based on the delayed closure of the sodium channels. With further exposure to cold or continued exercise, the action potential continues to build as a result. Only in warmth and at rest is the resting potential slowly rebuilt. However, this is in contrast to chloride ion channel myotonia, in which the resting potential is built up during physical exercise.
Symptoms, complaints, and signs
Paramyotonia congenita persists from birth, with symptoms remaining unchanged throughout life. Eyelid muscles, eye muscles, face, neck, and lower and upper extremities are particularly affected. For example, a closed eyelid cannot be opened for hours when exposed to cold. Cold exposure exists even when a damp and cool washcloth is applied. In addition, the patient’s face stiffens like a mask when exposed to cold. At the same time, there is impaired movement, with painless flexion of the fingers. The stiffness paradoxically increases with repeated movement and exposure to cold. Muscle weakness then occurs after sustained movement and exposure to cold. Some patients also suffer from periodic hyperkalemic paralysis beginning at puberty. In warm conditions, there are usually no symptoms at all or only minor symptoms.
Diagnosis and course of the disease
Myotonia congenita can be diagnosed as early as the onset of symptoms. Differential diagnosis between the different forms of myotonia is also straightforward.While the chloridion channel myotonies Myotonia congenita Thomsen and Myotonia congenita Becker have almost identical symptoms, they can be well differentiated from Paramyotonia congenita. A simple examination method is the application of cold compresses to induce eyelid myotonia. After that, it is impossible for the affected person to open the eyelids for a long time. At the same time, patients see double images, which should also always be asked about during the medical history. Increasing stiffness with repeated movement also points to sodium channel myotonia. In the blood, the elevated levels of creatinine kinase typical of muscle diseases are found. However, since these levels are also found in other diseases, they are irrelevant to the diagnosis. However, a genetic test can fully confirm the diagnosis.
Complications
With proper treatment of paramyotonia congenita, no complications occur. Life expectancy is not decreased. However, the major challenge, especially in winter, is to avoid cooling of the joints. In summer, the joints stiffen, among other things, when going to the bath. This causes stiffening of the joints and general physical weakness. The same applies to prolonged physical work. However, cooling cannot be completely avoided. This would only be achievable if those affected were to constantly stay in rooms with a higher temperature. Some patients also suffer psychologically from the fact that they can only perform many leisure activities to a limited extent. In individual cases, this can even lead to mental illness and depression. As a rule, no drug treatment is necessary for paramyotonia congenita. Simply avoiding cooling the joints is sufficient in most cases to prevent the stiffening. In a few cases, however, the symptoms may be so severe that treatment with the drug mexiletine is recommended. However, treatment with this drug, which is actually used to treat cardiac arrhythmias, should only be carried out as an exception, as it can lead to various side effects. For example, dizziness, mood swings, visual disturbances or nausea are often noticed when taking the drug. In very rare cases, thrombocytopenia with increased bleeding tendency may also occur.
When should you see a doctor?
Musculoskeletal disorders are a sign of impaired health. They should be evaluated by a physician so that a treatment and therapy plan can be developed. The first indications appear in the first days or months of life. If muscle stiffness occurs during exposure to cold or intense physical activity, a visit to the doctor is advisable. If the stiffness persists for several hours, this is an indication of paramyotonia congenita. If movement of the joints takes place, the stiffness increases by a further amount. The symptoms of the genetic disease remain constant throughout life without medical care and do not increase in intensity. Disturbances of the movement sequences, a fixed flexion of the joints as well as paralysis should be examined by a physician. A characteristic feature of the disease is absence of symptoms under warm environmental conditions. If irritations occur in coping with everyday life or sports activities as well as occupational activities cannot be fulfilled as desired, a doctor is needed. An increased risk of falls or accidents, gait instability and anxiety should be discussed with a physician. If emotional problems or psychological disturbance patterns appear at the same time due to the physical limitations, a clarification of the complaints is necessary. If the affected person complains about changes in vision during the muscle stiffness, there is a need for action. Frequently, double vision is documented during the phase.
Treatment and therapy
Causative treatment of paramyotonia congenita is not possible because it is a genetic condition. In most cases, however, no treatment is necessary if exposure to cold and strenuous physical activity are avoided. No reliable data are available on drug treatment. However, the use of the drug mexiletine is recommended to relieve long-lasting stiffness. Since this drug is a cardiac agent, attention should be paid to any side effects that may occur.
Outlook and prognosis
The condition, called paramyotonia congenita, is characterized by hyperexcitability of skeletal muscles. This leads to involuntary muscle contractions. Nevertheless, life expectancy is not limited. The prognosis for paramyotonia congenita is therefore positive. The relatively rare hereditary disease is inherited in an autosomal dominant manner. The musculature of the affected person cramps involuntarily. They can only be relaxed again with difficulty. It is difficult to tense and relax when climbing stairs. People affected by paramyotonia congenita experience problems especially when exposed to cold or after prolonged sitting. They have difficulty walking, grasping or keeping their balance. The involuntary muscular spasms make them more prone to falls than others. Despite paramyotonia congenita, there is no muscle weakness. Affected individuals may well have an athletic physique. The constantly contracting muscles create a kind of training effect. The symptoms are improved by targeted training. The aim of this is to neutralize the relaxation disorder and weaken its effect. In most cases, this works quite well. The treating physicians therefore rather rarely consider a short-term drug therapy. A cure for paramyotonia congenita is currently not possible. The disease is already established in childhood. It persists throughout life. Affected individuals may have increased risks for respiratory disease or respiratory paralysis due to myopathies if they require intensive medical care.
Prevention
Prevention of paramyotonia congenita is not possible because of its genetic cause. However, if the disease is present, extensive freedom from symptoms can be achieved if a few rules are observed. It is important to avoid cold influences, bathing in cool waters and prolonged physical activity. However, since the relationship between these influences and symptoms is obvious, sufferers will essentially follow these rules.
Follow-up
In many cases, only limited measures of aftercare are available to the affected person in paramyotonia congenita. First and foremost, a quick and, above all, an early diagnosis should be made to prevent further complications or other complaints in the affected person. The earlier a doctor is consulted, the better the further course of the disease usually is, so that the affected person should ideally consult a doctor at the first signs and symptoms of the disease. Most patients with paramyotonia congenita are dependent on the measures of physiotherapy and physiotherapy. In this case, many of the exercises from these therapies can also be performed in the patient’s own home to restore mobility to the body. In many cases, paramyotonia congenita is also treated by taking various medications. The affected person should always make sure to take them regularly and as prescribed in order to properly alleviate the symptoms. In case of ambiguity or if there are any questions, a doctor should always be consulted first. A doctor should also be consulted first in case of severe side effects. Possibly, paramyotonia congenita also reduces the life expectancy of the affected person.
What you can do yourself
Patients suffering from paramyotonia congenita are very sensitive to cold. Therefore, to prevent myotonic reactions from occurring, they need to keep their muscles warm. Especially in the winter months, it is therefore important to avoid cold. Warm clothing and heated rooms are essential during the cold season. There are also some challenges in the summer, as a cold swimming lake also causes the characteristic muscle tension. In everyday life, even cold tap water in the face can cause paralysis. Depending on how severe the symptoms are, the doctor may recommend drug treatment. Here, care must be taken to ensure the correct dosage. Medicines alleviate the problem, but they also have side effects. If sufferers know the cause of their sudden muscle stiffness, they learn how to deal with it. For example, sufferers warm the washcloth before using it and wait until the water is warm before holding their hands under the open faucet. Muscle tension can be exacerbated by physical activity. Therefore, too much exercise is not recommended for patients.If stiffness occurs, it helps to act quickly and warm the affected body parts.
