Crystal arthropathy (MSK) Flashcards
Define gout.
Acute inflammatory monoarthritis, caused by precipitation of monosodium urate crystals in joints
What is gout characterised by? (4)
- hyperuricaemia and deposition of urate crystals causing attacks of acute inflammatory arthritis
- tophi around the joints and possible joint destruction
- renal glomerular, tubular and interstitial disease
- uric acid urolithiasis
Which joints are commonly affected in gout?
- first toe (podagra)
- foot
- ankle
- knee
- fingers
- wrist
- elbow
- however, it can affect any joint
What are the primary sources of uric acid?
Purine + pyrimidine (nitrogen-containing heterocycles, DNA components) - released when cells broken down
What is the strongest risk factor for crystal arthropathy?
Hyperuricaemia
What are the causes of hyperuricaemia (crystal arthropathy)?
- increased urate intake/production:
- overproduction - tumour lysis syndrome
- increased nucleic acid turnover e.g. lymphoma, leukaemia, psoriasis
- increased dietary intake of purines - shellfish, anchovies, red meat
- decreased renal excretion of uric acid:
- renal failure / CKD
- thiazide/loop diuretics (and other drugs e.g. ciclosporin)
- alcohol excess
- dehydration
- idiopathic
Describe the pathophysiology of gout.
- hyperuricaemia –> deposition of monosodium urate crystals in joint + soft tissues + kidneys –> acute inflammation and pain –> areas of slower blood flow + poorer solubility of uric acid –> precipitation e.g. joints and kidney tubules
- overtime repeated gout attacks can cause destruction of joint tissue = arthritis –> chronic gout
What is chronic gout?
Repeated gout attacks –> chronic gout - permanent deposits of urate crystals (tophi) which form along the bones below the skin
A type of arthritis with joint tissue destruction + permanent joint deformity + tophi
What is pseudogout?
Deposition of calcium pyrophosphate crystals within the joint space (articular cartilage), often secondary to joint damage (e.g. OA, trauma)
Name a risk factor for pseudogout.
Hyperparathyroidism - due to increased serum calcium
What are the clinical features of gout? (6)
- sudden severe monoarticular pain
- stiff, red, swollen, warm joint
- asymmetrical joint distribution (can be polyarticular)
- podagra - painful big toe MTP
- tophi - over extensor surface joints e.g. elbows, knees, Achilles tendon
- acute attacks after large meal with purine-rich foods e.g. red meat, seafood, alcohol
Describe the disease course of gout.
- symptoms peak at 24h and resolve over 7-10 days
- acute attacks (with cellulitis, polyarticular or periarticular involvement) after large meals containing purine-rich foods e.g. red meat, seafood, alcohol
- attacks often recurrent + symptom-free between acute attacks
- intercritical gout = asymptomatic period between acute attacks
- repeat acute attacks –> chronic tophaceous gout
What are the features of chronic tophaceous gout? (4)
- persistent low-grade fever
- polyarticular pain with painful tophi (urate deposits)
- best seen on tendons and pinna of ear
- symptoms of urate urolithiasis (renal calculi symptoms)
Where are tophi found in gout?
Present over extensor surface joints:
- elbows
- knees
- Achilles tendons
What are the clinical features of pseudogout? (4)
- pain and swelling
- knee common, ankle, shoulder, elbow, wrist
- longer duration of acute attacks than gout (several days to weeks)
- chronic: pain, stiffness, functional impairment
What do you see on examination in gout/pseudogout?
Acute episodic arthritis: painful, warm, erythematous + swollen joint –> decreased range of motion –> disability
What are the risk factors for gout? (7)
- older age
- male
- meat and seafood
- alcohol
- drugs: diuretics, ciclosporin, tacrolimus, pyrazinamide, aspirin
- genetic susceptibility
- high cell turnover rate
What are the risk factors for pseudogout? (8)
- advanced age
- injury
- hyperparathyroidism
- haemochromatosis
- Fx CPPD
- hypomagnesaemia
- hypophosphatasia
- gout
What is the 1st-line investigation in crystal arthropathy?
Arthrocentesis with synovial fluid analysis
What does arthrocentesis with synovial fluid analysis show in gout vs pseudogout?
- gout: monosodium urate crystals, needle-shaped, negatively birefringent, (yellow under parallel light and blue under perpendicular light)
- pseudogout: calcium pyrophosphate crystals, rhomboid/brick-shaped, positively birefringent, (blue under parallel light and yellow under perpendicular light)
Following an acute episode, what should be checked in gout?
- once settled down, serum urate levels checked 2 weeks later (if falsely normal/low uric acid levels at time of flare)
- uric acid levels may be high, or falsely normal/low during the attack
- raised in gout: >420micromol/L in men; >360micromol/L in women
What would an X-ray show in gout vs pseudogout?
- gout: rat-bite erosions (may have overhanging edge or punched-out appearance), tophi in chronic
- pseudogout: chondrocalcinosis (CPPD deposition –> cartilage calcification), maybe signs of OA (LOSS)
What must you exclude in crystal arthropathy and how?
Septic arthritis - by gram stain and culture
What might you see on abdominal XR/KUB in gout?
Uric acid renal stones may be seen
