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CASE FILES: BIOCHEMISTRY
A N SW E R S TO C A SE 43: G O U T
Summary:
A 47-year-old male presents with an acute onset of right toe pain in
the middle of night after drinking alcohol and no history of trauma or any other
joint pain.
Diagnosis: Gouty arthritis.
Confirming diagnosis: Demonstration of the presence of the
monosodium urate crystals within the synovial leukocytes or in material
derived from tophi under polarizing microscopy.
Pathophysiology: Increased conversion of purine bases to uric acid or
a decreased excretion of uric acid by the kidney. Elevated levels of the
insoluble uric acid result in precipitation of urate crystals in the joints.
C L IN IC A L C O R R E L A T IO N
Gout is a disorder that occurs when uric acid crystallizes in the joints of the
body, usually the great toe or large joints. Hyperuricemia is a clinical condi-
tion characterized by elevated levels of uric acid. This leads to the formation
of sodium urate crystals, which are found primarily in the joints of the extrem-
ities and in the renal interstitium. The presence of urate crystals is associated
with extreme swelling and tenderness in the joints of the extremities. This con-
dition is often referred to as gout or gouty arthritis. In this condition, elevated
levels of uric acid are detectable in the blood and urine, and definitive diagno-
sis can be made by observing the presence of urate crystals in synovial fluid
removed from affected joints. The preference of urate crystal formation in the
joints of the extremities, such as the big toe, is thought to be associated with
the decreased temperature of the extremities that aids in urate crystal forma-
tion when levels exceed solubility.
A PPR O A C H TO U R IC A C ID C R Y ST A L L IZ A T IO N
O bjectives
1.
Be familiar with the uric acid pathway.
2.
Know about purine base metabolism.
3.
Be aware of treatment of gout with allopurinol and colchicine.
D efinitions
Allopurinol: An inhibitor of the enzyme xanthine oxidase used to treat
gout to decrease the amount of sodium urate in the blood and thus pre-
vent its crystallization in the joints.
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