Muscular dystrophy

Synonyms

Muscle wasting, progressive muscular dystrophy; Duchenne muscular dystrophy, Becker-Kiener dystrophy, myotonic dystrophy, Facio-scapulo-humeral muscular dystrophy, FSHD

Summary

Muscular dystrophies are congenital diseases of the muscles that lead to a progressive loss of muscle mass and increasing weakness via a disruption in the structure and / or metabolic processes of the muscles. So far, more than 30 different forms of muscular dystrophy are known, the predominant symptoms, frequency, course and prognosis z. T. clearly differentiate. The underlying genetic defect is known for many muscular dystrophy diseases, which enables genetic diagnosis (examination of the genetic material).
A causal therapy for muscular dystrophy does not yet exist, so the focus is on symptomatic therapies that are intended to alleviate the consequences of the disease and improve the quality of life of those affected.

definition

The term muscular dystrophy encompasses congenital diseases of the muscles that lead to a progressive loss of muscle mass and number and are noticeable through weakness in the affected muscle groups (muscle loss). So far, more than 30 different forms of muscular dystrophy are known, which differ in inheritance, affected muscle parts, onset of symptoms and severity of the clinical course. In some muscular dystrophies, the heart muscles are also affected.

Forms of muscular dystrophy and characteristics

• Duchenne type: Early onset, infestation of the Heart muscles, severe course, most common form, almost exclusively affects boys.

• Becker-Kiener type: Symptoms similar to those of Duchenne muscular dystrophy, but later onset, somewhat milder course, also almost exclusively affects boys

• Facio-scapulo-humeral muscular dystrophy: milder form, onset in young adulthood, initially affects the muscles of the shoulder girdle and face, men and women are affected equally often.

frequency

Overall, the frequency of muscular dystrophies is estimated at 1: 2000 to 1: 5000, whereby the individual muscular dystrophy diseases show differences in inheritance and frequency in the population. Of the above, the Duchenne (approx. 1: 5000) and Becker-Kiener muscular dystrophy (approx. 1: 60000) belong to the x-linked recessive inherited diseases and therefore almost exclusively affect boys and men. Facio-scapulo-humeral muscular dystrophy (approx. 1: 20,000), on the other hand, is inherited in an autosomal dominant manner, which is why men and women are affected equally often.

causes

The causes of progressive muscle wasting and weakness are congenital defects in the structure of muscle cells and in muscle metabolism. In many muscular dystrophies, however, the exact mechanism of the disease has not yet been clarified.

Symptoms

Those affected are noticeable by an increasing weakness of the affected parts of the body, which under certain circumstances can give clues to the underlying form of the muscular dystrophy through the localization.
In contrast to other diseases that manifest as weakness or muscle wasting (e.g. diseases of the nerves or spinal cord; Spinal stenosis), muscular dystrophies retain their own muscular reflexes and sense of feeling. If the heart muscles are affected, it comes to one Heart failure (Heart failure), the infestation of the Respiratory muscles leads to shortness of breath and promotes respiratory infections (e.g. lung infection).

The onset of symptoms is very different between the individual forms: While severe forms such as Duchenne muscular dystrophy are already apparent in childhood, benign forms may not become apparent until advanced adulthood, e.g. B. diagnosed as the cause of bad posture.

Diagnosis

The basis of the diagnosis is the question of the occurrence of similar complaints in family members (family history) in order to confirm the suspicion of an inherited disease. Muscular dystrophy occurs spontaneously only in the rarest of cases (so-called "New mutation") on. The physical examination reveals the weakness and reduction in size ("atrophy") of the affected muscle parts with largely preserved muscle reflexes and the absence of, for example, sensory disorders or involuntary muscle twitching. The distribution of muscle weakness and wasting on certain parts of the body can provide important diagnostic information. The blood test may show an increase in muscle enzymes (substances from the muscle cells), which suggest damage to muscle cells, but this is of minor diagnostic importance.

Further diagnostic steps can be initiated to differentiate it from other diseases that can clinically lead to a similar picture. Here v. a. Diseases of the nerves and the spinal cord as well as the neuromuscular endplate, the switching point between nerve and muscle, can be excluded. Serve z. B the record of Nerve conduction velocity (NLG) and the electrical muscle activity (Electromyography, EMG).
The microscopic examination of a sample of affected muscles taken during a minor surgical procedure (Muscle biopsy) shows a characteristic picture in all forms of muscular dystrophy, which differs from that in z. B. differentiates nerve diseases.

Ultimately, with the many muscular dystrophies, specific changes in the genome of those affected are known and can be detected using special diagnostic methods. This can be done in human genetic centers larger clinics.

Differential diagnoses

Muscle weakness and wasting can appear as symptoms of a number of other diseases that may need to be ruled out. These include above all:

• Nerve and spinal cord disorders, e.g. B. poliomyelitis ('poliomyelitis'), Amyotrophic Lateral Sclerosis or multiple sclerosis. Exclusion is based on the clinical picture, measurement of the nerve conduction velocity and electrical muscle activity, which differ from the findings in muscular dystrophy. A muscle biopsy can also provide information about the underlying nerve damage.
• Diseases of the "neuromuscular endplate", the switching point between nerve and muscle, which are caused by autoimmune processes. These include myasthenia gravis or Lambert-Eaton syndrome, which can also occur in the wake of tumor diseases. Here, too, there are characteristic differences in the electromyogram, the nerve conduction velocity and the muscle biopsy. Autoantibodies that would be detectable in the blood and microscopic specimen in the aforementioned diseases are absent in muscular dystrophies.

therapy

To date, there is no causal therapy for muscular dystrophies. Attempts at drug therapy with a wide variety of substances that have been carried out to date have ultimately all been disappointing. For the future, hopes lie in a genetic therapy that eliminates the underlying defects in the genetic make-up or their effects on muscle metabolism, but such attempts are currently only in their early stages.

Therefore, the therapy of muscular dystrophies is currently based on supportive measures, which are intended to cushion the consequences of increasing muscle weakness and to support the patient in coping with everyday life. This includes above all physiotherapy to maintain the greatest possible mobility and to prevent bad posture.
Body training should only be done very carefully in order to avoid consequential damage to the muscles due to overload.
The use of anabolic steroids is not advisable due to serious side effects and unproven benefits and is justifiable in exceptional cases, under the strict supervision of a specialized doctor. A psychotherapeutic care can help those affected cope with a diagnosis of a chronically progressive disease; contact with one of the numerous self-help groups can facilitate access to offers of help. As with all hereditary diseases, genetic counseling is advisable for further family planning; the sense and benefit of prenatal diagnosis must be decided on a case-by-case basis.

Forecast:

The prognosis depends largely on the involvement of the heart and respiratory muscles and is therefore quite different between the various muscular dystrophies. While z. For example, if the Duchenne type leads to death from heart failure or respiratory infections at a young age, life expectancy is not restricted for more benign forms. However, even milder forms of muscular dystrophy can lead to severe impairments in everyday life and quality of life during the course of the disease.