Gout

Description

Alternative Names

Diagnosis

Determining which joints are affected is an obvious first step in any diagnosis. A physical examination and medical history can reveal a number of significant indictors that help confirm or rule out gout. The following are some examples:

• Gout is more likely if arthritis first appears in the big toe than if it first appears elsewhere.
• The speed of the onset of pain and swelling is relevant; symptoms that take days or weeks rather than hours to develop probably indicate a disorder other than gout.
• Abnormal enlargements in joints that had been affected by previous injury or osteoarthritis are possible signs of gout. This is particularly significant in older women on diuretics.

Examination of Synovial Fluid

Examination of synovial fluid is the most accurate method for diagnosing gout. It may even be helpful in detecting gout during intercritical periods. The synovial fluid is the lubricating liquid that fills the synovium (the membrane that surrounds a joint and creates a protective sac). The fluid cushions joints and supplies nutrients and oxygen to cartilage, the slippery tissue that coats the ends of bones.

Procedure. The procedure for taking a sample of synovial fluid from an affected joint is called aspiration:

• A needle attached to a syringe is inserted into the joint and suction is used to draw the fluid into the syringe.
• Local anesthesia is avoided because it can reduce the effectiveness of aspiration, but normally the procedure is only mildly uncomfortable.
• Following the procedure there can be some minor discomfort in the area where the needle was inserted, but it usually dissipates quickly.

Aspiration can cause infection, though this occurs in less than 0.1% of patients. Aspiration sometimes eases a patients symptoms by reducing swelling and pressure on the tissue surrounding the joint.

Analyzing the Fluid. After the sample is taken, it is sent to a laboratory, where a specialist examines the sample through a microscope under polarized light. This special light will reveal the presence of monosodium urate (MSU) crystals, which will nearly always confirm a diagnosis of gout. The laboratory can also test the sample for infection.

Blood Test for Uric Acid Levels

A blood test is usually given for measuring uric acid and detecting hyperuricemia. A low level of uric acid in the blood makes a diagnosis of gout much less probable, and a very high level increases the likelihood of gout. Some experts argue, however, that such measurements are not very useful, given what is known about the variability of uric acid levels in people with gout:

• Uric acid levels in the blood during an attack of gout can lie within or below the normal range.
• Even if hyperuricemia is present, it is very common in the population and does not necessarily indicate the presence of gout.

Determining Uric Acid Excretion in Urine

It is sometimes helpful to gauge the amount of uric acid excreted by the patient, particularly if the patient is young and has pronounced hyperuricemia that might be related to a metabolic disorder. If uric acid exceeds a particular value in the urine, further tests for an enzyme defect or other identifiable cause of gout arising from uric acid overproduction are justified. Greater-than-normal amounts of uric acid in the urine also indicate that the patient faces a greater risk of developing uric acid kidney stones, and can guide the physician in his or her choice of drug therapy for chronic gout.

24-Hour Urine Sample. Typically, urine samples are taken over the course of 24 hours. To provide a urine sample, the following steps are taken:

• The urine is collected during an intercritical period, after the patient has been placed on a purine-reduced diet. The patient is also asked to temporarily stop using alcohol and any medications that can interfere with the test.
• The patient should not change any of his or her usual eating or drinking patterns when performing this test.
• The patient discards the first urination on the day of the test.
• Afterward all urine passed over the next 24 hours is collected, including the first urination on the morning of day two.
• The container is then delivered to the patients physician or sent directly to the laboratory.

Imaging Techniques

X-Rays. For the most part, X-rays do not reveal any abnormalities during the early stages of gout, and their usefulness where gout is concerned lies in assessing the progress of the disorder in its chronic phase and in identifying other health problems whose symptoms may resemble those of gout. Tophi can be seen on X-rays before they become apparent on physical examination.

Advanced Imaging Techniques. Advanced imaging techniques being investigated for identifying tophi include computed tomography (CT), magnetic resonance imaging (MRI), and Doppler ultrasonography. A 2002 study comparing these approaches found that CT scans offered the best images.

Ruling Out Other Disorders

As part of the diagnosis, other disorders that produce gout-like symptoms or cause hyperuricemia should be ruled out. In general, it is easy to distinguish acute gout that occurs in one joint from other arthritic conditions. The two disorders that may confuse this diagnosis are pseudogout and septic arthritis. Chronic gout can often resemble rheumatoid arthritis. A number of other conditions may at some point in their course resemble gout.

Pseudogout. Pseudogout is a condition most likely to be confused with gout.

Rheumatoid Arthritis. Rheumatoid arthritis can cause distortion in the joints of the fingers, inflammation, and pain that may mimic gout. It is particularly difficult to distinguish chronic gout in older people from rheumatoid arthritis. A proper diagnosis can be made with a detailed medical history, laboratory tests, and identification of MSU crystals.

Osteoarthritis. Gout can coincide and be confused with osteoarthritis in older people, particularly when it occurs in arthritic finger joints in women. In general, gout should be suspected if the joints in the fingers tips are unusually enlarged.

Infections. Joint infections can have features that resemble gout and a correct diagnosis is critical for appropriate treatment. For example, some cases of gout have been confused with infection after joint replacement. On the other hand, joint infection not associated with surgery might indicate sepsis, which is a widespread and potentially life-threatening bacterial infection that can cause inflamed joints, chills, and spiking fever. The severity of the fever and a high white-blood cell count in the joint fluid helps diagnose a septic infection, while identifying urate crystals in the joint is a good indicator of gout.

Charcot Foot. Between 1% and 2.5% of people with diabetes suffer from Charcot foot or Charcot joint (medically referred to as neuropathic arthropathy). This condition is caused by abnormalities in the nerves in the feet. Early changes may resemble gout, with the foot becoming swollen, red, and warm. Recognition and treatment of this condition is very important. A seriously affected foot can become deformed. The bones may crack, splinter, and erode, and the joints may shift, change shape, and become unstable.

Bunions. A bunion is a deformity that usually occurs at the head of the first of five long bones (the metatarsal bones) that extend from the arch and connect to the toes and may be confused with gout. The first metatarsal bone is the one that attaches to the big toe. A bunion begins to form when the big toe is forced in toward the rest of the toes, causing the head of the first metatarsal bone to jut out and rub against the side of the shoe; the underlying tissue becomes inflamed, and a painful bump forms. As this bony growth develops, the bunion is formed as the big toe is forced to grow at an increasing angle towards the rest of the toes.