Gout and Pseudogout
Gout is a type of crystal arthritis.
The other main type of crystal arthritis
is that in which calcium pyrophosphate crystals
are formed (pseudogout
- You can tell the difference between the two types if you aspirate the contents of a joint, and then view it under polarised red light:
- Urate crystals – are negatively birefringent – they will appear a needle shaped crystals (image below).
- Calcium phosphate crystals - are positively birefringent – they will appear as rhomboid shapes
- This is often a question in MCQ in exams !
Gout is a disorder resulting from high concentration of uric acid in the blood stream. However, not all patients with a high blood urate level get gout, and having a low blood urate level does not rule out gout as a diagnosis!
- More common in men (M:F – 10:1)
- Incidence is increasing in women due to the wider use of thiazide diuretics.
- Age of onset usually 40-60
- Rare before puberty
- Rare in premenopausal women
- Urate levels in the blood rise naturally with age
- Multifactorial. Genetic components, but other factors also involved. In bit like diabetes in that in a genetically susceptible individual, certain circumstances may trigger the condition.
- Diet – meat and alcohol increase the risk
- Foods that have a high concentration of purine
- Socio-economic status – more prevalent in richer populations – “Rich Man’s disease” – possibly because of its associations with alcohol and an expensive diet.
- Body size – greater risk in larger body size
- Usually a monoarthritis
- Only polyarthritis in 10% of cases
- MTP is the joint affected in >65% of patients
- Also often affects the PIP’s and DIP’s
- Tophi – deposits of urate crystals in the skin. Chalky in texture. The MTP joint in the foot is the most common place for crystal deposition – gravity might play a role.
- Inflammatory Arthritis and synovitis – due to urate crystal deposition in the joints. The urate crystals are phagocytosed by neutrophils, but in the process, these cells release inflammatory cytokines, attracting more neutrophils, and setting off an inflammatory reaction, resulting in an inflammatory arthritis.
- The MTP of the first toe is most commonly affected.
- This neutrophilic mechanism is the same is calcium phosphate crystal arthritis
- The neutrophils quickly die off, and thus there is a rapid turnover of cells. This accelerates the inflammation. This is because the crystals are toxic to the cells.
- Warm, tender, painful joints
- Pyrexia is also often present
- Stone formation aka urolithiasis – in the kidney and bladder – may cause associated symptoms
- There may also be secondary pyelonephritis, although renal insufficiency is not usually caused by gout, and any proteinuria is probably age related, mild, and non-progressive