When only one joint is inflamed, meaning it has swelling, redness, heat, and pain, the condition is termed monoarticular arthritis. This means only one joint has arthritis.

There are a limited number of conditions that can cause this problem. They are: trauma; crystal-induced; infection or tumor.

Gout and pseudogout are frequent causes of acute monoarticular arthritis. They are among the most common forms of crystal-induced arthritis. Gout occurs more frequently in men and is rarely seen in premenopausal women. The great toe joint, ankle, and knee are the most commonly affected joints and are usually very painful, swollen, red, and warm.

Condition such as kidney malfunction and kidney transplantation increase the risk of gout. One major reason, particularly with kidney transplant patients, is the use of drugs such as cyclosporine or tacrolimus.

Unfortunately, this creates a clinical picture where many joints can become swollen and inflamed leading to a misdiagnosis of rheumatoid arthritis.

The diagnosis of gout is confirmed by the presence of monosodium urate crystals in joint fluid. The joint fluid must be examined using a polarizing microscope. That is why it is best looked at in a rheumatologist's office rather than a large commercial lab where the personnel are not used to looking at joint fluid and may not have access to a polarizing microscope.

The joint fluid is inflammatory, with a white blood cell (WBC) count in the 10,000-20,000 range and made up of a specific type of white blood cell called the polymorphonuclear leukocyte. An elevated uric acid is frequently seen, but approximately 30% of patients may have a normal uric acid level at the time of attack.

Pseudogout usually occurs in the elderly and commonly involves the knee, ankle, and wrist. The diagnosis is confirmed by the presence of calcium pyrophosphate dihydrate crystals (CPPD) in an inflammatory joint fluid. The diagnosis is suggested by the presence of chondrocalcinosis on x-ray. Chondrocalcinosis is calcified tissue that often shows up as white lines in the cartilage.

Like gout, the majority of the attacks get better over several days even if untreated. Chronic calcium pyrophosphate dihydrate crystal deposition may occur in the setting of severe osteoarthritis. Sometimes there is a genetic tendency also.

Septic arthritis is always a concern. Septic arthritis refers to a condition where a joint becomes infected with a bacterium.

Patients generally have a fever, fatigue, and feel lousy.

The joint is generally warm, red, and swollen, and painful. The most common organism responsible is N gonorrhoeae, the germ that causes gonorrhea.

The next most common bacteria are Staphylococcus or Streptococcus. Patients whose immune system is compromised such as alcoholics, diabetics, intravenous-drug abusers, or immunosuppressed patients can be infected with a number of different bacteria.

Any patient with a single inflamed joint should have a joint aspiration using a needle so that the fluid can be analyzed.

Gonococcal arthritis, the arthritis due to gonorrhea, is the most common type of septic arthritis. It occurs in sexually active adults. Most patients present with aches and pains that go jump from joint to joint, inflamed tendons, and 1 or 2 swollen painful joints. A recent history of sexual exposure is often reported. A peculiar type of skin rash may accompany the aches and pains. The diagnosis is hard to make because the bacteria is hard to culture.

Cancers can involve the joint and present as an arthritis affecting one joint. A metastasis (cancer spreading) can result in a severely painful joint.

The diagnosis can frequently be made by imaging either with plain x-rays or magnetic resonance imaging. Biopsy of the lining of the joint arthroscopically (using a small telescope) may be necessary to confirm the diagnosis.

A very peculiar and unusual condition, pigmented villonodular synovitis, is a benign tumor that can result in inflammation of a single joint. This tumor most commonly affects the knee, hip, and finger. Magnetic resonance imaging may be helpful with the diagnosis.

Arthroscopic biopsy may be needed. The treatment is surgical removal of the lining of the joint.