Gout is one of the most common metabolic diseases. An inborn error of metabolism will, in susceptible individuals, lead to excessive production of uric acid and subsequent deposits of monosodium urate. Gouty arthritis is caused by the deposition of monosodium urate crystals inside joints. This leads to a potentially destructive type of inflammatory arthritis.

In addition to arthritis, deposits of monosodium urate can accumulate and induce an inflammatory response in other areas such as the subcutaneous tissues around joints and in the kidneys. These deposits can grow and become quite large.

These growths are called "tophi." Infiltration of the kidneys by monosodium urate can lead to significant kidney damage if allowed to go unchecked.

Making the accurate diagnosis of gout is important because it is a very treatable disease. Criteria established by the American College of Rheumatology (ACR) include clinical factors such as...

• More than 1 attack of acute arthritis
• Maximum inflammation within one day
• Attack of arthritis affecting one joint
• Joint redness
• Involvement of the great toe joint
• One-sided great toe inflammation
• One-sided foot inflammation
• Suspected tophus (deposit or accumulation of uric acid crystals under the skin)

Laboratory factors such as

• Elevated blood uric acid
• Negative culture of joint fluid

And x-ray factors like...

• Non-symmetric joint swelling on x-ray
• Bony cysts on x-ray

The gold standard for diagnosis is the demonstration of monosodium urate crystals inside a joint or tophus of a patient with suspected gout. Examination of material is performed using a polarizing microscope. The experience and expertise of the person looking for crystals is key.

The diagnosis of gout can be ascertained with absolute certainty by demonstrating the presence of monosodium urate crystals or with relative degree of certainty if a patient has at least 6 of 12 ACR diagnostic criteria.

One important diagnostic point is that dependence on seeing an elevated blood uric acid level alone is insufficient to aid in making the diagnosis. This is because up to 40 per cent of patients with a true acute attack of gout will have normal blood levels and 10 per cent of normal men and postmenopausal women will have an abnormally elevated blood uric acid.

Recently, diagnostic ultrasound has been recognized as an important tool for demonstrating the presence of tophi as well as characteristic joint abnormalities in patients with suspected gout.

In further articles I will discuss management.