Muscle disease--a primer

True weakness, especially in the proximal muscles, is a symptom of muscle disease. In differential diagnosis, conditions mimicking myopathy can be excluded on the basis of physical findings, various tests, and when appropriate, muscle biopsy. Once myopathy has been diagnosed, the physician needs to determine whether the cause is toxic, endocrine, inflammatory, metabolic, dystrophic, or congenital. The distinguishing features of these categories help in reaching a specific diagnosis. Because most of the common myopathies can be treated, recognition is important.