A clinical approach to muscle diseases.

Muscle diseases constitute a large variety of both acquired and hereditary disorders that can affect muscle structure, metabolism, or the function of the muscle channel. A successful clinical approach to a patient with a suspected myopathy is based on a thorough medical history and neurological examination. Associated clinical symptoms such as myoglobinuria, contractures, myotonia, cardiac disease, and respiratory insufficiency can be extremely helpful in limiting the differential diagnosis. In addition, a phenotypic approach to diagnosis according to the patient's predominant pattern of weakness is essential for guiding the physician in selecting the most appropriate diagnostic studies. Although muscle biopsy remains a useful tool, molecular genetic studies are now available for the noninvasive diagnosis of many muscle diseases.