Understanding Arthritis

Understanding Arthritis - what causes it

Pathophysiology

Rheumatoid Arthritis

The disease process within the joints (intraarticular) begins as an inflammation of the synovium with edema, vascular congestion, fibrin exudate, and cellular infiltrate. The inflammatory process is set off by some sort of irritation or damage to joint tissue. This is called a “triggering” event. White blood cells rush into the area, releasing chemicals useful in destroying bacteria but also harmful to tissue cells. Also released are prostaglandins (mediate inflammation), leukotrienes (producers of inflammation) and digestive enzymes. Particularly damaging to joint tissue is the enzyme collagenase, because it breaks down collagen, the main structural protein of connective tissue. The early manifestations of the disease may include weight loss, fever, and generalized aching and body malaise. Early morning stiffness lasting a few minutes to an hour or more is characteristic. This kind of discomfort commonly referred to as fibrositis, is poorly localized.

The proximal interphalangeal and metacarpophalangeal joints of the hands and the metatarsophalangeal joints of the feet are often affected early. As the disease progresses, the fingers develop a characteristic tapering appearance with a classic ulnar deviation of the hand. Inflammation of the tendon sheaths, particularly in the wrist may occur. There is spasm of the muscles attached to the involved joints. Rheumatoid arthritis may also affect other body systems and rheumatoid nodules may form in the heart, lungs, and spleen. Manifestations of the multisystem involvement of rheumatoid arthritis include pleuritus, pulmonary fibrosis, pericarditis, aortic valve disease, lympadenopathy, glaucoma, and splenomegaly.

Bacterial Arthritis

Synovial tissues respond to a bacterial invasion by becoming inflamed. The joint cavity may become involved, and pus will be present in the synovial membrane and the synovial fluid. If allowed to progress, the infection will cause abscesses in the synovium and subchrondral bone, eventually destroying cartilage. Ankylosis of the joint may result. The patient will complain of pain, swelling, and tenderness of the joint.

Osteoarthritis

Both primary and secondary degenerative joint diseases affect the articular cartilage. Characteristic pathologic changes include the following:

• Erosion of articular cartilage

• Thickening of bone underneath the cartilage

• Formation of osteophytes or bone spur

Normal articular cartilage when affected by the disease becomes yellow and opaque. Areas of cartilage soften, and the surface becomes rough, frayed, and cracked. This process is thought to occur as a result of digestion of the cartilage enzymes and alteration of the nutrition of the cartilage. Eventually, the cartilage is destroyed, and the underlying subchrondral bone goes through a remodeling process.

Gouty Arthritis (gout)

Urate crystals form in the synovial tissue, causing severe inflammation. The inflammatory process is extremely rapid, occurring over a few hours. Acute symptoms are extreme pain, swelling and erythema of the involved joints. Typically, the first metatarsophalangeal joint of the great toe is involved (podagra), but other joints, such as the ankle, heel, knee, or wrists, may also be affected. Pain is so severe that the patient may not tolerate even the weight of the sheet over the joint. Between attacks of gouty arthritis, the patient may be asymptomatic, but repeated attacks can occur gradually with increasing frequency if the disease is untreated. Patients may develop tophi, or deposits of monosodium urate in their tissues. These consist of a core of monosodium urate with a surrounding inflammatory reaction. Patients with tophaceous deposits tend to have more frequent and more severe episodes of gouty arthritis.