Crystal-induced arthropathies Flashcards
Compare the crystal type of gout & pseudogout
Gout:
- Monosodium urate (MSU)
- Negative birefringence (yellow when parallel to compensator filter), needle-shaped
Pseudogout:
- Calcium pyrophosphate dihydrate (CPPD)
- Positive birefringence (blue when parallel), rhomboid-shaped
Compare the Rx of gout & pseudogout
Gout:
NSAIDs, corticosteroids, colchicine, Allopurinol, febuxistat
Pseudogout:
NSAIDs, corticosteroids
Define gout
derangement in purine metabolism resulting in hyperuricemia; monosodium urate crystal deposits in tissues (tophi) and synovium (microtophi)
Causes of gout
• sources of uric acid: diet and endogenous
• synthesis:
hypoxanthine -> xanthine -> uric acid. both steps catalyzed by xanthine oxidase
Who typically gets gout?
- most common in males >45 yr old
* extremely rare in premenopausal female
An acute gout attack may mimic cellulitis. How can it be differentiated?
Joint mobility is
preserved in cellulitis.
Gout often affects more than one joint
(i.e. ankle, midfoot and MTPs).
What are precipitants of gout?
Drugs are FACT
- Furosemide
- Aspirin®/Alcohol
- Cytotoxic drugs
- Thiazide diuretics
Foods are SALT
- Seafood
- Alcohol (beer and spirits)
- Liver and kidney
- Turkey (meat)
Causes of hyperuricemia (gout)
Primary or genetic
- idiopathic renal underexcretion (90%)
- idiopathic overproduction or abnormal enzyme production/function
Secondary
- dietary excess (particularly high consumption of beer, seafood, and meat)
- underexcretion (>90%): renal failure, drugs, systemic conditions
- overproduction (
Px of gout (think of different organs affected)
- single episode progressing to recurrent episodes of acute inflammatory arthritis
- acute gouty arthritis: severe pain, redness, joint swelling, usually involving lower extremities. Can self resolve within days to weeks.
- tophi: urate deposits on cartilage, tendons, bursae, soft tissues, and synovial membranes. common sites: first MTP, ear helix, olecranon bursae, tendon insertions (common in Achilles tendon)
- kidney: gouty nephropathy, uric acid calculi
Where do gout tophi commonly deposit?
first MTP, ear helix, olecranon bursae, tendon insertions (common in Achilles tendon)
Ix of gout
- joint aspirate: >90% of joint aspirates show crystals of monosodium urate (negatively birefringent, needle-shaped)
- x-rays may show tophi as soft tissue swelling, punched-out lesions – erosion with “overhanging” edge
Rx of acute gout
- NSAIDs. high dose
- Corticosteroid
- Colchicine within first 12h
DO NOT start allopurinol during acute flare (makes it worse)
Rx of chronic gout
- avoid precipitant foods & drugs
- antihyperuricemic drugs (Allopurinol, febuxostat): xanthine oxidase inhibitors
- Uricosuric drugs (probenecid, sulfinpyrazone): if intolerant to allopurinol. C/I in renal failure
Indications for antihyperuricemic medications in gout
recurrent attacks, tophi, bone erosions, urate kidney stones.
Perhaps in renal dysfunction with very high urate load (controversial)
Pathophysiology of pseudogout
acute inflammatory arthritis due to phagocytosis of IgG-coated calcium pyrophosphate
dihydrate (CPPD) crystals by neutrophils and subsequent release of inflammatory mediators within joint space
