Gout is a crystal arthropathy due to deposition of monosodium urate (MSU) crystals in and around the joints.

Typically occurs in those above 40 years. There is a strong male predilection of 20:1.

Characterised by monosodium urate crystals deposition in periarticular soft tissues. The crystals are needle-shaped and are strongly birefringent in plane polarised light 10. The synovial fluid is generally a poor solvent for monosodium urate and therefore causes crystallisation at low temperatures. The crystals are chemotactic and activate complement.

There are five recognised stages of gout:

  1. asymptomatic hyperuricaemia
  2. acute gouty arthritis
  3. intercritical gout (between acute attacks)
  4. chronic tophaceous gout
  5. gouty nephropathy
Risk factors
Location

Usually has an asymmetrical polyarticular distribution:

  • joints: 1st MTP joint most common (known as podagra when it involves this joint); hands and feet are also common
  • less common: bones, tendon, bursa

Most radiographic findings include the skeletal system.

Plain radiograph

Characteristic radiologic changes occur in the chronic stage, though not all patients progress to this. There is a predilection for the small joints of the hands and feet. Chondrocalcinosis is present in ~5%.

Joints
  • joint effusion (earliest sign)
  • preservation of joint space until late stages of the disease
  • absence of periarticular osteopenia
  • eccentric erosions
  • the typical appearance is the presence of well-defined “punched-out” erosions with sclerotic margins in a marginal and juxta-articular distribution, with overhanging edges (see case 12) also known as rat bite erosions
Bone
  • punched-out lytic bone lesions
  • overhanging sclerotic margins
  • avascular necrosis
  • mineralisation is normal
Surrounding soft tissues
  • tophi: pathognomonic
  • olecranon and prepatellar bursitis
  • periarticular soft tissue swelling due to crystal deposition in tophi around the joints is common
  • the soft tissue swelling may be hyperdense due to the crystals, and the tophi can calcify (uncommon in the absence of renal disease)
Ultrasound

While there can be variation in appearance, tophi tend to be hyperechoic, heterogeneous, have poorly defined contours. They can be multiple grouped and surrounded by anechoic halos 8.

CT

Findings generally reflect those on the plain radiograph.

Dual energy CT can distinguish between urate mineralisation and calcification, which may be useful for cases where the clinical and biochemical presentation is atypical11.

MRI

Signal characteristics of gouty tophi are usually:

  • T1: isointense
  • T2
    • variable 4
    • majority of lesions are characteristically heterogeneously hypointense
  • T1 C+ (Gd): tophus often enhances
Arthritides
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Article information

rID: 1395
Section: Pathology
Synonyms or Alternate Spellings:
  • Monosodium urate arthropathy
  • Gouty arthropathy
  • Tophaceous gout
  • Gouty arthritis

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Cases and figures

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    Figure 1: podagra (by James Gillray)
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    Gouty arthritis w...
    Case 1: foot
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    Case 2
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    Foot Ap
    Case 3
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    Case 4
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    Case 5: chronic tophaceous gout
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    Case 6
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    Case 7
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    Case 8
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    Case 9
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    Case 10: knee
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    Case 10: elbow
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    Case 11
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    Case 12: tophaceous gout
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    Case 13
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    Case 14
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    Case 15: tophaceous gout
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