Muscle diseases occur in all age groups and can cause serious physical disability. Their impact is especially severe when children and young adults are affected. The needs of these patients are numerous and complicated, and frequently not adequately met. Some muscle diseases respond well to medical treatment, while many of the physical disabilities can be improved or prevented. Hence, although muscle diseases are not as common as neurological disorders such as stroke or epilepsy, they deserve our full attention.
Types of muscle diseases
There are many different forms of muscle diseases, with different causes and outcome, and requiring different treatments. They can be divided into two major categories.
Symptoms of muscle diseases include:
Quite often, the weakness is associated with muscle wasting. Although muscle aches and cramps may occur in muscle diseases, these symptoms are more commonly due to other causes such as muscle strain. Easy fatigue with weakness is typically associated with myasthenia gravis. Episodic paralysis is a distinctive symptom in the periodic paralyses.
The muscular dystrophies
The muscular dystrophies are a group of muscle diseases, each caused by a specific gene abnormality, with progressive muscle wasting, weakness and contractures. Although the abnormal gene is often inherited, it can also occur spontaneously. These diseases can arise even when no one else in the family is affected.
Some muscular dystrophies are very severe, while others cause only mild symptoms. In children, the most common is Duchenne muscular dystrophy, a severe muscle disease which usually only affect boys. Unlike girls, affected boys do not have a second X-chromosome to compensate for an X-chromosome carrying the abnormal gene. Weakness is noticed as they begin to walk or run. Characteristic signs include walking on tiptoe and large calves. The disease occurs in one out of every 3000 newborn male children.
Other relatively common forms of muscular dystrophy include limb girdle muscular dystrophy, facioscapulohumeral muscular dystrophy and myotonic dystrophy. Both sexes are affected, as the abnormal genes are not in the X-chromosome. These diseases may start in adulthood or childhood.
Besides weakness and wasting, myotonic dystrophy causes muscle stiffness with difficulty in relaxation called myotonia. In some muscular dystrophies, the heart may also be involved.
The inflammatory muscle diseases
When the patient’s immune system damages the body’s own muscle tissues, the result is an inflammatory muscle disease.
Three main types of inflammatory muscle diseases are identified:
These diseases usually affect adults, although dermatomyositis may also affect children.
Patients with these diseases develop progressive weakness of the hip and shoulder muscles over a few weeks or months, sometimes with difficulty in swallowing. In the case of dermatomyositis, a characteristic rash may occur. It is very important to correctly diagnose these disorders because polymyositis and dermatomyositis can be treated effectively with drugs that suppress the immune system.
In myasthenia gravis, the body’s immune system inappropriately injures a specialised muscle structure called the acetylcholine receptor. Damage to these receptors leads to the typical symptom of this disease, namely easy fatigue and increased weakness on exertion.
Often, the eyes are affected with drooping of the upper eyelids and double vision. Generalised weakness and difficulty with swallowing or speaking is common. This disease will also respond effectively to treatments that suppress the immune system.
Cover picture shows a combined cytochrome oxidase and succinic dehydrogenase stain: Mitochondrial myopathy showing COX negative fibres, including a “ragged red fibre”.
The NNI provides a comprehensive and specialised service for the diagnosis and care of muscle diseases. Medical consultations are offered at the Neuromuscular Clinics, which are staffed by neurologists with special expertise in muscle diseases. The Neurodiagnostic Laboratory conducts electromyography and nerve conduction studies, useful tests that examine electrical signals derived from muscle and nerve.
The Neuromuscular Laboratory provides muscle histology studies, which are often essential for the specific diagnosis of muscle diseases. For these studies, a small sample of muscle is first obtained, usually under local anaesthesia. The sample is then cut into thin sections and stained with a battery of stains for examination and analysis. Techniques used include histochemistry, immunohistochemistry and electron microscopy. Gene tests for several inherited muscle diseases will soon be available following the setting up of the Neurogenetics Laboratory.
Physical therapy and physical aids may be required to help extend independence and prevent complications. If the disease is genetic or inherited, counselling patients on the disease’s inheritance pattern will help them to make informed choices in planning for the future. Social or psychological assistance may be needed. The fundamental goal is to help and encourage patients and their families surmount the challenges of muscle disease to achieve an active and fulfilling life.
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