Muscle Disease - A Guide
Muscle diseases occur in all age groups and can cause significant physical disability. Their impact is especially serious when children and young adults are affected. The needs of these patients are diverse 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 other neurological disorders such as stroke or epilepsy, they deserve our fullest attention.
The Many Kinds of Muscle Diseases
There are many different types of muscle diseases, with different causes and outcome, and requiring different treatments. For simplicity, we can divide muscle diseases into two major categories - those that are genetic, i.e. related to a disordered gene, and those that are not genetic. The genetic muscle diseases include a very wide range of diseases, the best known of which are the muscular dystrophies. Other genetic muscle diseases include the congenital myopathies, storage myopathies, mitochondrial diseases and the periodic paralyses. The muscles disease which are not genetic (i.e. acquired) are also diverse. The most important among these are the inflammatory muscle diseases. These are autoimmune diseases in which the body's own immune system inappropriately injures its muscles. A related autoimmune disease is myasthenia gravis. Rarely, viruses and parasites may also cause certain forms of inflammatory muscle disease. Other non-genetic muscle diseases may be due to drugs or hormonal disorders.
What are the symptoms of muscle diseases?
The primary complaint of patients with muscle diseases is weakness, which is usually progressive, bilateral, and involves muscles close to the trunk, i.e hip and shoulder muscles. The patient may notice difficulty in walking or running, climbing stairs, getting up from sitting, carrying heavy loads, lifting or reaching above the shoulders. In infants and young children, this weakness may show up as loss of tone, and delay in the ability to stand, walk or run. 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 certainly arise even when no one else in the family is affected.
Some muscular dystrophies are very severe, while others cause only mild symptoms. Among children, the most common is Duchenne muscular dystrophy, a severe muscle disease which usually only affects boys. Unlike girls, affected boys do not have a second X-chromosome to compensate for an abnormal X-chromosome, in which the abnormal gene resides. Weakness is noticed as they begin to walk or run. One characteristic sign is enlargement of the calf muscles. The disease occurs in about one out of every 3000 new born 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 in these diseases do not reside in the X-chromosome. These diseases can start in adult life as well as in 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.
Considerable advances have been made in our understanding of the muscular dystrophies within the past one or two decades. We now know which genes are abnormal and what they do in many muscular dystrophies. For example, we know that in Duchenne muscular dystrophy, the abnormal gene codes for a protein in the membrane of the muscle cell. Absence of this protein causes membrane breakdown and muscle damage. Such scientific breakthroughs bring hope that a cure will be found for the muscular dystrophies. Already, scientists have begun studies using gene therapy to introduce normal genes into diseased muscle.
The Inflammatory Muscle Diseases
When the patient's immune system becomes disordered and attacks the body's own muscle tissues, the result is an inflammatory muscle disease. Three main types of inflammatory muscle diseases are identified - polymyositis, dermatomyositis and inclusion body myositis. These diseases usually affect adults, although dermatomyositis may also affect children. Patients with these disease 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.
Mention must be made of a related disease called myasthenia gravis, which is not uncommon. In myasthenia gravis, the body's immune system inappropriately injures the muscle receptors at the junction of between nerve and muscle. 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. Difficulty with swallowing and speaking is also common besides generalised weakness. This disease, like the inflammatory muscle diseases, will respond effectively to treatments that suppress the immune system.
Services at National Neuroscience Institute
The National Neuroscience Institute provides a comprehensive, specialised and advanced service for the diagnosis and care of muscle diseases. Medical consultations are offered at the Neuromuscular Clinic in the Neuroscience Outpatient Clinics. The Electrophysiology Laboratory conducts electromyography and nerve conduction studies, which examine electrical signals derived from muscle and nerve. The Institute has recently set up a Neuromuscular Laboratory to provide a muscle histology service. Muscle histology is often essential for the specific diagnosis of muscle diseases. In this process, under local or general anesthesia, a small sample of muscle is obtained for study. It is cut into thin sections and stained for examination and analysis. Techniques used include histochemistry, immunohistochemistry, Western blotting and electron microscopy.
We strongly believe that the patient with muscle disease must be treated with awareness of the range of problems associated with the disease - medical, physical, genetic, psychological, and social. The first step is always an accurate diagnosis, because specific medical treatment and genetic counselling can only be given with an accurate diagnosis. Physiotherapy and physical aids may be required to help extend physical independence and prevent complications such as joint contractures. Counselling the patient and family on the inheritance pattern of a genetic muscle disease helps them 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 and achieve a useful and fulfilling life.