occurred. Pain is usually not prominent but may occur with muscle cramps or spasms during physical activity. How rapidly weakness occurs and other historical clues help make a specific diagnosis. A patient with a severe influenza infection may rapidly weaken from viral- induced breakdown of muscle fibers, the byproducts of which may precipitate in renal Various medications tubules, leading to kidney failure (myoglobinuria, rhabdomyolysis). may adversely affect muscle over periods of weeks to months, such as statin drugs given to patients with high cholesterol levels or patients on corticosteroids for rheumatological diseases. Endocrine disorders like Cushing's disease and hypothyroidism can cause myopathy. Muscle pain or weakness developing primarily during exercise may signal a hereditary condition involving glycogen or lipid metabolism in muscle. Some of the more chronically developing myopathies may also be hereditary in nature, where a detailed family history is crucial, followed by examination of other affected relatives. The diagnostic testing in myopathy supplements any historical findings and physical signs, and includes measurement of serum creatine kinase (CK), a muscle enzyme often nonspecifically elevated in diseases of muscle. EMG testing helps to confirm the diagnosis and rules out other causes of weakness from neuropathy, myasthenia, or motor neuron disease. In selected patients a muscle biopsy is performed for a pathological diagnosis.