Myalgia or muscle pain is a symptom of many diseases. It is most likely to be caused by over-exertion or trauma of the muscle. However, if there is no history of either, an infection is the next most likely cause.
Long lasting myalgia can be caused by a metabolic problem, certain types of malnutrition and chronic fatigue syndrome.
When House suffered his infarction, myalgia was the only symptom.