According to WebMD, chronic muscle pain is likely caused by a condition known as myofascial pain syndrome, or MPS. Another possible cause is fibromyalgia, which is the most common musculoskeletal condition after osteoarthritis. MPS is usually somewhat localized to specific trigger or tender points, while fibromyalgia can be experienced as a general, all-over-body pain.
WebMD states that MPS can be caused by injury, repetitive motion or lack of activity. It is diagnosed by identifying a trigger point that responds painfully to touch or pressure. MPS can be treated with physical therapy, massage therapy, pain medications and trigger point injections.
According to WebMD, fibromyalgia is a far more complicated condition that doctors still do not fully understand. Most often, people experience unexplained pain over various areas of the body. This is accompanied by fatigue. The pain is not the result of an injury or any type of definable cause. Fibromyalgia pain can have debilitating effects on a person's life and often leads to depression. Additional symptoms include irritable bowel syndrome; incontinence; abdominal pain; inability to concentrate; dryness in mouth, nose and eyes; numbness or tingling in the fingers and feet; chronic headaches; and stiffness. Because a source is usually not pinpointed, WebMD states that doctors have a difficult time treating fibromyalgia.