Duchenne Muscular Dystrophy (DMD)
It is the commonest form of muscular dystrophy which is transmitted as X-linked recessive trait, occurring mainly in boys the females acting as carriers. Its incidence ranges from 3-5 per 100,000 live births per year. Gene for DMD has been identified.
Duchene gene is located on the short arm of the X-chromosme 21. The protein product of this gene is dystrophin which is absent or grossly deficient in DMD. It is present in reduced quantity in young boys who show a much slower progression of the disease.
Clinically the child (a boy) presents with inability to walk and walks with clumsiness and a tendency to fall, There is inability to run or hop. The onset is gradual and generally before the age of 4 years.
Characteristically the child has a waddling gait and a characteristic physical sign called Gower ‘s where in order to arise from a seated, stooping or supine position, he pushes himself up by climbing on his knees and thighs with his hands.
There is enlargement, pseudohypertrophy of muscles of the calf mainly but the disease can affect other muscles as well like glutei, quadriceps, infraspinti and deltoid. Though these muscles are firm to touch and enlarged but they are weak.
Gradually weakness and wasting of muscles deveiops but the muscles of face and hand escape. The peculiar distribution of muscular weakness leads to a posture of lordosis when patient stands up.
Fasciculations are absent. Tendon reflexes are usually diminished. As the disease progresses, there is not only kyphoscoliosis but also weakness of respiratory muscles leading to recurrent pulmonary infections.
Because of involvement of muscles at different rates in opposing group of muscles, contractures may occur in the feet leading to inversion and plantar flexion. With progressive loss of muscle power ability to carry out, all movements and activities are progressively lost and the child may be crippled and confined to a wheel chair.
Many children with DMD have mental impairment and below average 10. Some suffer from difficulty in sleeping and getting a comfortable sleep.
Cardiac involvement occurs leading to cardiac arrhythmias. There are tall R waves in right precordial leads and deep 0 waves in the limb and left precordial leads.
Diagnosis of DMD is based on clinical presentation, rise in CPK levels which are elevated 20-100 times the normal. The levels of this enzyme are abnormal at birth so a diagnosis of affected child can be made at an early stage.
Electromyography shows presence of brief small amplitude potentials. Muscle biopsy shows muscle fibers of varying size with local areas of degenerating and regenerating muscle fibres. There is increased amount of fat and connective tissue replacing lost muscle fibers. In doubtful cases, diagnosis can be confirmed by dystrophin immunoblotting.
There is no treatment for DMD. Vit. E has been used in laige doses but its role is doubtful. Prednisone in dose of 40 mg/day is effective in increasing muscle strength and function and slowing the rate of deterioration.
Main attempt is directed towards stretching exercises and physiotherapy to minimize contractures. A spinal brace may be advised to reduce deterioration of posture. In some cases knee anide and foot arthosis are advised to keep the patient mobile. A life long routine of daily active and passive exercise is necessary to prevent formation of contractures.
The course of the disease is progressive and gradually all group of muscles are involved. Death usually occurs in 10-12 years as a result of cardiac failure, respiratory failure or respiratory infections. For further prevention of disease in affected family genetic counseling is essential.
Becker Muscular Dystrophy (BMD)
This is less severe form of X-linked recessive myopathy and its clinical picture is similar to that of DMD. Its onset is slow and is usually recognized after the age of 5. Many patients are able to walk upto adolescence.
There is enlargement of calf muscle but mental retardation is not marked. Since it is a genetically linked defect with defect of dystrophin, its progression is there. High levels of CPK, electromyography and muscle biopsy confirm the diagnosis.
Faclo Scapulohumeral Muscular Dystrophy
It is transmitted as an autosomal dominant trait with incomplete penetrance. Onset of the disease is generally in the second to fourth decade. Its progress is slow. Hall mark of the disease is weakness of facial muscles which gives rise to a placid, expressionless face.
Weakness of shoulder gridle muscles leads to difficulty in raising arms above shoulder level. Biceps and triceps are involved early in the disease but deltoid is spared. Muscles of forearm are hypertrophied.
Diagnosis is made by raised levels of CPK. Further confirmation is done by EMG and muscle biopsy. Since it is a very slow form of disease, life expectancy is not affected.
Limb gridle muscular dystrophy
It is transmitted as an autosomal recessive trait. It may begin at any age and affects both men and women. Its course is intermediate between that of DMD and facio scapular humeral.
There is primary involvement of the limb gridle muscles. Weakness may begin before age of 5 or as late as third decade, starting in two thirds of cases in shoulder and remaining one third in the pelvic gridle.
There is either difficulty in walking up stairs or raising their arms depending on which group of muscles are involved. There may be hypertrophy of calf and other muscles. Gradually patient develops lordosis and protuberance of abdomen.
Some patients may develop cardiomyopathy. Respiratory failure develops in those with long standing disease. Diagnosis is confirmed by raised levels of CPK, EMG and muscle biopsy which show active myopathy.
This is a rare autosomal dominant disorder which begins in middle life and can affect both males and females. It begins with involvement of ocular muscles leading to bilateral ptosis and progressive opthalmoplegia. Diplopia is rare.
In later life involvement of pharyngeal muscles results in form of oculopharyngeal dystrophy which is characterized in addition with dysphagia.
The disease has an autosomal dominant made of inheritance with an unstable mutant gene on the long arm of cohoromasome 19 (19q 13.3). The most common age of involvement is between 20-40 years involving both sexes.
The patient usually has difficulty in relaxing his/her grasp after shaking hands. There is muscle weakness associated with wasting and myotonia. This is confined to facial muscles, and masseter. Frontal baldness usually accompanies these changes.
Besides this patient may develop catarct, mental retardation, hypogonadism cardiomyopathy, respiratory insufficiency and endocrinopathies. In males there is testicular atrophy and impotence while females suffer from menstrual irregularities.
Disease is slowly progressive and death usually occurs by the age of 50. Diagnosis is based on EMG which shows high frequency waxing and waning discharges and a myopathic pattern.
Enzyme levels are usually normal while muscle biopsy may show atrophy of muscle especially of Type I fibres.
Treatment. It is limited. Phenytoin (5mg/kg / day) is effective. Other drugs are quinine (300-600 mg BD) or procainamide (1-3 g/day).
Prognosis. It is a progressive disabling disorder. Death usually results either from cardiac or respiratory failure.