Arthritis

Causes and disease mechanisms. Gout is a form of inflammatory arthritis that results from the deposition of urate crystals in the synovium (Van Doornum and Ryan). Uric acid, the end product of metabolism of some important proteins, results from endogenous purine metabolism with an important, though minor dietary contribution. In other words, while diet has some impact on gout, the idea of gout as chiefly the result of too much rich food and drink (the "patrician malady") is untrue. Hyperuricemia is seen prior to episodes of arthritis and progesses to gout when large increases in body stores of uric acid make it impossible for the body to adapt. Synovial urate crystals activate inflammatory pathways either directly or after coating by proteins such as immunoglobulins.

Hyperuricemia (high uric acid levels in the blood) is common, with a male predominance; it involves 5 percent of men. Risk factors include obesity, renal disease, high alcohol intake, and diuretic use. It is also seen as part of "syndrome X," which consists of abdominal obesity and high blood pressure, and is a potent risk for arthroscelerosis and heart disease. Gout is less common, involving 0.2–0.5 percent of men.

Clinical features. Gout may be precipitated in patients with hyperuricemic gout by excess alcohol, metabolic disturbances due to surgery or trauma, or diuretic therapy. Classical gout involves the big toe (podagra), making it exquisitely painful, red, swollen, and tender. The onset may involve multiple joints, particularly those of the lower limbs. It is unusual for both lower limbs to be affected at the same time. Initial attacks often resolve after a few days and can be followed by recurrent episodes. These can progress to chronic arthritis. Some cases with established gout have subcutaenous urate crystals deposits (known as tophi) in the pinnae of the ears, fingers, and elbows.

Investigations. If joint fluid from an affected joint is aspired (which is often very difficult to do), detecting intracellular uric acid crystals under the microscope is diagnostic. Most patients have elevated serum uric acid levels, though only a minority of patients with hyperuricemia have gout. Acute attacks result in an elevated ESR and high white cell count. In established gout X-rays show punched-out erosions with sclerotic margins, often distant from the joint margins.

Figure 3 Heberden's and Bouchard's nodes SOURCE: Author