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There are many hereditary and acquired muscle diseases, and an accurate diagnosis is crucial for effective management. Diagnosis often involves specialist assessment and investigations such as electromyography and muscle biopsy. A number of common muscle diseases are explained and discussed below.

(a) DUCHENNE MUSCULAR DYSTROPHY

Duchenne muscular dystrophy is an X-linked trait that mostly affects males. It is characterized by diffuse skeletal and cardiac muscle involvement. It is universally fatal, with death occurring most commonly in late adolescence or early adulthood. Symptoms usually have their onset in early childhood with progressive muscle weakness. The focus of care at this early stage is on maximizing mobility and minimizing contractures and scoliosis. Between the ages of 8 and 11 years, affected children usually need a wheelchair and as the weakness progresses, they become increasingly dependent on carers for bathing, feeding and other personal care.

The physical symptoms most commonly encountered in the terminal stage result from respiratory failure secondary to muscle fatigue. Initially this may be present only during sleep, giving rise to symptoms such as irritability, nausea, headache and daytime somnolence. Scoliosis and retention of secretions compound respiratory muscle failure, and pneumonia is a frequent cause of death. Treatment interventions include spinal immobilization, mechanical clearing of secretions and ventilatory support. Advance-care planning is important.

Other problems suffered by these children include constipation, dysphagia (difficulty in eating), reflux, weight loss or weight gain, depression and heart failure.

(b) POLYMYOSITIS

Polymyositis has probably been overdiagnosed in the past, and currently includes a heterogeneous group of chronic inflammatory muscle diseases. An attempt is being made to define these disorders more precisely, on the basis of their pathophysiology.

There are usually clinical features of proximal limb-muscle weakness. Respiratory or cardiac muscle also can be involved. Swallowing may be affected. Raynaud's phenomenon, rash, arthritis and pulmonary fibrosis can occur. The creatine phosphokinase is usually elevated, often in proportion to muscle damage, with other enzymes (lactate dehydrogenase, aspartate aminotransaminase, alanine aminotransferase) usually also raised. Electromyography shows myopathic potentials, abnormal spontaneous activity, and fibrillation potentials.

Muscle biopsy histology shows muscle

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