Gout:

 Gout is a disorder characterized by high levels of uric acid—

the end product of purine catabolism—in blood (hyperuricemia),

as a result of either the overproduction or underexcretion of uric

acid. 

The hyperuricemia can lead to the deposition of mono -

sodium urate crystals in the joints, and an inflammatory response

to the crystals, causing first acute and then progressing to chronic

gouty arthritis. 

Nodular masses of monosodium urate crystals

(tophi) may be deposited in the soft tissues, resulting in chronic

tophaceous gout (Figure 22.16). 

Formation of uric acid stones in the kidney (urolithiasis) may also be seen. [Note: Hyperuricemia is typically asymptomatic and does not lead to gout, but gout is preceded

by hyperuricemia.] 

The definitive diagnosis of gout requires

aspiration and examination of synovial fluid (Figure 22.17) from

an affected joint (or material from a tophus) using polarized light

microscopy to confirm the presence of needle-shaped mono -

sodium urate crystals (Figure 22.18).

A diet rich in meat and seafood (particularly

shellfish) is associated with increased risk of

gout. In addition, a diet rich in low-fat dairy

products was shown to be associated with a

decreased risk.