Causes
The causes of progressive muscle atrophy and weakness are congenital defects in the structure of the muscle cells and in muscle metabolism. In many cases of muscular dystrophies, however, the exact mechanism of the disease has not yet been clarified.
Symptoms
The affected persons are conspicuous by an increasing weakness of affected body parts, which under certain circumstances can already give indications of the underlying form of muscular dystrophy by the localization. In contrast to other diseases that manifest themselves as weakness or muscular atrophy (e.g. diseases of the nerves or spinal cord; spinal canal stenosis), muscular dystrophies preserve muscle reflexes and senses. If the heart muscles are affected, this leads to cardiac insufficiency (cardiac insufficiency), the affection of the respiratory muscles leads to respiratory distress and promotes respiratory tract infections (e.g. pneumonia). The onset of the symptoms differs greatly between the different forms: While severe forms like Duchenne muscular dystrophy are noticed already in childhood, benign forms may be diagnosed only in advanced adulthood, e.g. as a cause of poor posture.
Diagnostics
The basis of the diagnosis is the question of the occurrence of similar symptoms in family members (family history), in order to confirm the suspicion of an inherited disease. Only in very rare cases does muscular dystrophy occur spontaneously (so-called “new mutation”). Physical examination reveals the weakness and reduction (“atrophy”) of affected muscle areas with largely preserved muscular reflexes and the absence of, for example, sensory disturbances or involuntary muscle twitching.
The distribution of muscle weakness and atrophy over certain parts of the body can provide important diagnostic indications.Blood tests may reveal an increase in muscle enzymes (substances from the muscle cells), which indicate damage to muscle cells, but this is diagnostically of secondary importance. Further diagnostic steps can be taken to differentiate it from other diseases that may lead to a similar clinical picture. In this case, diseases of the nerves and spinal cord as well as of the neuromuscular endplate, the switch point between nerve and muscle, must be excluded.
This can be achieved by recording the nerve conduction velocity (NLG) and 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 for all forms of muscular dystrophy, which differs from that of e.g. nervous disorders. Ultimately, specific changes in the genetic make-up of the affected muscles are known in many muscular dystrophies and can be detected using special diagnostic procedures. This can be done in human genetic centers of larger hospitals.
