Crystal Arthritis (gout and pseudogout) Flashcards
enzymatic pathway for production of uric acid
Hypoxanthine –> xanthine –> uric acid
via xanthene oxidase
allopurinol, febuxostat target
xanthene oxidase
describe normal uric acid handleing in the kidney
Filtered at glomerulus (100%)
reabs by: URAT-1 → GLUT9 → circulation (98%)
secreted by OAT → urine (5-10%)
What is uricase
enzyme that normally breaks down urate
epidemiology of gout
purine rich diet (red meat, seafood)
alcohol (beer) abuse
Men > women
older people
In general how do you get hyperuricemia?
make too much uric acid or don’t get rid of enough
**the later is the cause of hyperuricemia in 90% of cases
congenital causes of hyperuricemia?
- HGPRT deficiency (Lesch-Nyhan syndrome)–> surplus substrate (PRPP)
- G6PD deficiency (interferes with renal excretion)
- Fructose-1-phosphae adolase deficiency
- Phyosphoribosyl-pyrophosphate synthase overactivity
secondary causes of increased uric acid production
increased cell turnover • leukemia/lymphoma • tumor lysis syndrome • treating psoriasis • sickle cell disease, etc
What drugs cause decreased secretion of uric acid
o Thiazide and loop diuretics
o Low dose aspirin/salicylates: blocks secretion
o Ethanol
o Cyclosporine
also, Nicotinic acid, Pyrazinamide and Ethambutol
how does DM lead to hyperuricemia
enhances uric acid reabs
pathophys of gout
hyperuricemia –> uric acid ppt and forms crystals
–> Urate crystals are recognized as a foreign substance by macrophages, fibroblasts, and mast cells and activate NLRP3 inflammasome → release of IL-1Beta → neutrophils influx into joint and are activated → IL-8, TNF released + neutrophil cell lysis → INFLAMMATION
Presentation of gout
Sudden onset of agonizing pain, swelling ad redness of first MTP joint
Raised serum uric acid levels (>6.8 mg/dL)
Trophi (more with chronic)
Leuckocytosis
Gout can occur at any time but is often precipitated by
- too much food or alcohol (beer in particular)
- dehydration
- starting a diuretic
- illness or stress
in skin and around joints = Smooth white deposits
trophi
Elicits a granulomatous reaction = macrophages
chronic gout
–> erosive arthritis