Hyperuricemia is a pathological elevation of serum uric acid levels. Gout is a clinical consequence of this condition, characterized by the deposition of uric acid crystals (urate) in tissues and the development of chronic inflammation.
Key enzymeXanthine oxidase, responsible for uric acid synthesis.
Morphological outcomeFormation of gouty granulomas and nodules known as *tophi urici*.
Renal complicationsUrate nephropathy, nephrolithiasis, and risk of renal failure.
Inflammatory mechanismActivation of phagocytes, cytokine release (IL-1, IL-6, TNF-α), and immune autoaggression.
Mechanisms of Hyperuricemia
Hyperuricemia occurs when there is an imbalance between the production and excretion of uric acid.
Secondary form: Develops due to massive cell turnover (hemoblastoses, chemotherapy, alcoholism) or decreased renal excretory function.
The primary source of urates is the breakdown of purine nucleotides, which increases during intense physical exertion or excessive dietary purine intake (meat, fish, chocolate).
Pathogenesis of Gouty Inflammation
When urate concentrations exceed a critical threshold, they crystallize in tissues. This triggers a cascade of pathological reactions:
System activation: Complement, kinin, and hemostatic systems are involved.
Chemotaxis: Leukocytes migrate to the site of crystal deposition.
Phagocytosis: Leukocytes attempt to engulf the crystals, leading to cellular damage and the release of inflammatory mediators.
Autoaggression: Damaged tissues act as a source of autoantigens, sustaining the chronic inflammatory process.
Systemic Manifestations
Gout affects more than just joints. Systemic effects include:
Hypertension: Due to increased vascular sensitivity to catecholamines.
Renal pathology: Urate deposition leads to nephrosclerosis and urolithiasis.
Metabolic shifts: Disturbances in carbohydrate and lipid metabolism may occur, contributing to ketoacidosis.
Mnemonic
"Urates in joints — tophis in kidneys, purines in diet — gout in the quiet." Remember the triad: phagocytosis, inflammatory mediators, and tissue damage.
Frequently asked questions
What genetic defects lead to primary hyperuricemia?
Primary hyperuricemia is caused by genetically determined defects in purine metabolism enzymes. These hereditary enzymopathies include:
Which joints are most commonly affected during the first acute gout attack?
Typical locations for an acute gout attack include the joints of the feet, especially:
First metatarsophalangeal joint — the classic location for gouty arthritis;
Ankle joint.
A sudden gout attack is characterized by severe pain and inflammation peaking within 24 hours, intense swelling, and erythema.
Which pharmacological agents are used to inhibit xanthine oxidase?
Agents used to inhibit xanthine oxidase include:
Allopurinol — a structural analog of hypoxanthine, a competitive and 'suicide' inhibitor of xanthine oxidase; it reduces uric acid production while excreting hypoxanthine and xanthine, which are more water-soluble.
Febuxostat — a non-purine selective inhibitor of xanthine oxidase.
Does hyperuricemia always lead to gout?
No, hyperuricemia does not always cause gout. The risk of developing the disease is directly proportional to urate levels, but additional factors are required for clinical manifestation.
What is Lesch-Nyhan syndrome?
It is a hereditary disorder caused by a deficiency of the enzyme hypoxanthine-guanine phosphoribosyltransferase, leading to the overproduction of uric acid.
Why do the kidneys suffer in gout?
The kidneys are affected due to the accumulation of uric acid crystals in the parenchyma and urinary tract, causing nephrolithiasis, pyelonephritis, and ultimately nephrosclerosis.
Go deeper
Role of xanthine oxidase in purine metabolism
Differential diagnosis of primary and secondary hyperuricemia
Impact of cytostatics on uric acid levels in oncology patients
Mechanisms of ketoacidosis development in purine metabolism disorders
Immunological aspects of gouty granuloma formation