Crystal Arthropathy

Question 1

Define Crystal Arhtropathies

Answer 1

Gout = disorder of uric acid metabolism leading to monosodium urate crystal deposition in the joints, soft tissues and kidneys, causing recurrent bouts of acute arthritis.

Pseudogout = arthritis associated with deposition of calcium pyrophosphate dihydrate (CPPD) crystals in joint cartilage

Question 2

Aetiology and risk factors of gout

Answer 2

Hyperuricaemia:

• Increased urate intake or production (10%): increased dietary intake, lymphoma, leukaemia, polycythamia vera, psoriasis, Lesch-Nyhan syndrome
• Decreased renal excretion (90%): idiopathic, drugs (Ciclosporin, alcohol, thiazides, loop diuretics - see CANT LEAP), renal dysfunction

RF: older age, male, menopausal, drugs, obesity, insulin resistance, HTN, renal insufficiency, hyperlipidaemia, FMHx

Question 3

Aetiology of risk factors of pseudogout

Answer 3

CPPD crystal formation initiated in cartilage located near the surface of the chondrocytes
Excessive cartilage pyrophosphate production -> local calcium pyrophosphate supersaturation + CPPD crystal formation/deposition

Predisposed by osteoarthritis, trauma, haemochromatosis, hyperpararthyroidism

RF: advanced age, injury

Question 4

Symptoms of gout

Answer 4

Episodes of acute pain attacks (rapid onset | severe | monoarticular | commonly first metatarsophalangeal joint | peaks at 24 hours | resolves 7-10 days | precipitated by trauma, infection, alcohol)
Asymptomatic between attacks
Joint stiffness
Swelling
Tenderness
Chronic tophaceous gout: follow repeated acute attacks - persistent low-grade fever, polyarticular pain with painful tophi on the tendons and pinna of ear
Symptoms of urate urolithiasis (kidney involvement)

Question 5

Symptoms of pseudogout

Answer 5

Painful and tender joints
- Acute: painful, swollen knee, ankle, shoulder, elbow, wrist
- Chronic: pain, stiffness, functional impairment
Sudden worsening of osteoarthritis
Red and swollen joints
Fever and malaise
Tendonitis, tenosynovitis, bursitis (rare)

Question 6

Signs of gout on examination

Answer 6

Tophi 
Joint stiffness
Foot joint distribution 
Swelling and join effusion 
Tophi
Erythema and warmth

Question 7

Signs of pseudogout on examination

Answer 7

Acute arthritis: Red, hot, tender, restricted range of movement, fever
Chronic arthropathy: bony swelling, crepitus, deformity, restriction of movement

Question 8

Investigations for gout

Answer 8

Arthrocentesis with synovial fluid analysis: raised WBC | strong negative birefringent needle-shaped crystals under polarised light, MC+S -ve)

Serum uric acid level: elevated
FBC: raised WCC
ESR: raised

AXR/KUB film: uric acid renal stones may be visible
USS: erosions, tophi, double contour line
X-ray affected joint: peri-articular erosions (overhanging edge, punched out appearance), “rat-bite” erosions

Question 9

Investigations for pseudogout

Answer 9

Arthrocentesis with synovial fluid analysis: Intracellular/extracellular positively birefringent rhomboid-shaped crystals

Calcium: normal/elevated
PTH: normal/elevated
Magnesium: normal/decreased
Hypophosphataemia 
Alk phos: normal/reduced
FBC: WCC raised
ESR: raised

X-ray affected joint: Linear, stippled, radio-opaque deposits in cartilage of joints | loss of joint space | osteophytes | subchondral cysts | sclerosis