Illnesses that cause chronic muscle and joint pain?

Pains that seem to be coming from joints can sometimes be coming from structures outside the joints, such as ligaments, tendons, or muscles. Examples of such disorders are bursitis and tendinitis.

True joint pain (arthralgia) may or not be accompanied by joint inflammation (arthritis). The most common symptom of joint inflammation is pain. Inflamed joints may also be warm and swollen, and less often the overlying skin may be red. Arthritis may involve only joints of the limbs or also joints of the central part of the skeleton, such as the spine or pelvis. Pain may occur only when a joint is moved or also be present at rest. Other symptoms, such as rash, fever, eye pain, or mouth sores, may be present depending on the cause of the joint pain.

Different disorders tend to affect different numbers of joints. Because of this, doctors consider different causes of pain when the pain affects one joint (see Joint Pain: Single Joint) than when it affects more than one joint. When multiple joints are involved, some disorders are more likely to affect the same joint on both sides of the body (for example, both knees or both hands) than other disorders. This is termed symmetric arthritis. Also, in some disorders, an attack of arthritis remains in the same joints throughout the attack. In other disorders, the arthritis moves from joint to joint (migratory arthritis).

In most cases, the cause of pain originating inside multiple joints is arthritis. Disorders that cause arthritis may differ from each other in certain tendencies, such as the following:

How many and which joints they usually involve

Whether the central part of the skeleton, such as the spine or pelvis, is typically involved

Whether arthritis is sudden (acute) or longstanding (chronic)

Acute arthritis affecting multiple joints is most often due to

Viral infection

The beginning of a joint disorder or a flare up of an existing chronic joint disorder (such as rheumatoid arthritis or psoriatic arthritis)

Less common causes of acute arthritis in multiple joints include Lyme disease (which also may affect only one joint), gonorrhea and streptococcal bacterial infections, reactive arthritis (arthritis that develops after an infection of the digestive or urinary tract), and gout.