Gout

Question 1

Define crystal arthropathy (gout, pseudogout)

Answer 1

GOUT:

• A disorder of uric acid metabolism causing recurrent bouts of acute arthritis caused by deposition of MSU crystals in joints, and also soft tissues and kidney

Question 2

Explain the aetiology / risk factors of crystal arthropathy (gout) (11)

Answer 2

RISK FACTORS:

• Older age
• Male
• Post-menopause
• Use of thiazide & loop diuretics
• Obesity
• Hypertension
• Diabetes mellitus
• Consumption of meat, seafood, alcohol
• FHx of gout
• Increased cell turnover
  
  • haematological malignancies,
  • myeloproliferative disorders
  • psoriasis
  • chemotherapy-induced cell death)
• Use of nephrotoxic agents

AETIOLOGY

• Uric acid is the end product of purine breakdown which normally circulates at low levels in plasma and synovial fluid
• Hyperuricaemia can occur due to either: REDUCED RENAL EXCRETION (90%) and/or INCREASED URATE (10%)
• Reduced renal excretion:
  
  • Idiopathic
  • Thiazide diuretics
  • Renal dysfunction
• Increased urate:
  
  • Increased purine consumption: Red meat, Seafood
  • Increased alcohol
  • Increased cell turnover (e.g. haematological malignancies, myeloproliferative disorders, psoriasis, and chemotherapy-induced cell death)
  • Genetic enzyme deficiencies (G6PD, HPRT)

Question 3

Summarise the epidemiology of Gout

Answer 3

• 10 x more common in MALES
• Very rare pre-puberty
• Rare in pre-menopausal women

Question 4

Recognise the presenting symptoms of crystal arthropathy (gout) -CHRONIC & ACUTE

Answer 4

• Sudden-onset severe joint pain (usually affects 1st MTP called PODAGRA) - SELF-LIMITED
• Erythematous and swollen joint
• Mostly feet joints affected
• Usually mono/oligoarticular involvement

Patients sre symptom-free between attacks but repeared acute attacks lead to Chronic gout:

• Tophi (extra-articular MSU depositions) on pinna of ear, fingers, olecranon
• Persistent low-grade fever
• Urolithiasis (renal colic)

Question 5

Recognise the signs of crystal arthropathy (gout, pseudogout) on physical examination

Answer 5

• Extremely tender, red, hot, swollen joint
• Presence of tophi
• May be slightly febrile
• Costo-vertebral angle (CVA) tenderness (if urolithiasis)

Question 6

Identify appropriate investigations for crystal arthropathy (gout, pseudogout) and interpret the results (4)

Answer 6

• Arthrocentesis (synovial fluid assessment - to assess for septic arthritis):
  
  • Presence of strongly neGatively birefringent needle shaped crystals seen on polarising microscopy (G for gout)
  • Rasied WCC (>2000)
• Serum uric acid: raised
• Measure uric levels 6 weeks after episode
• X-ray/ultrasound of joint: can show tophi (CT) peri-articular and METAPHYSEAL “rat-bite” erosions, osteophytes/overhanging edge (X-ray)
• CT-KUB: Check for stones

Question 7

Management

Answer 7

Acute phase - control inflammation

• Colchicine + NSAIDs (colchicine can cause diarrhoea)
• Can add prednisone if refractive (can inject steroid if knee gout)

Long term - urate reducing therapy

2 attacks in a year is required for long-term urate-reducing therapy (can give after 1st attack in clinical practice)

• Allopurinol
  
  • Initially give with colchicine as initiation/up-titration of allopurinol can precipitate an acute attack
  • monitor for agranulocytosis ➔ warn about sore throat
  • Can cause rashes (SJS/TEN/DRESS) - discontinue immediately and re-introduce cautiously in mild rash
• Check urate levels after commencing (should be <300 a year after starting)

Allopurinol should be continued during an acute attack in patients presenting with an acute flare of gout who are already established on treatment