Gout

Imaging of gout: from ultrasound to MRI

Various imaging modalities allow the assessment of different aspects of joint involvement in gouty arthritis:

• Ultrasound (US): Demonstrates crystal deposition directly within the synovial membrane as well as on the articular cartilage surface. Developing synovitis is accompanied by an increased effusion volume and local enhancement of echogenic density.
• Dual-energy CT (DECT): An indispensable tool in ambiguous diagnoses. The method is based on the ability of tissues to attenuate X-rays to different degrees. Using special color-mapping, the scanner clearly highlights areas of uric acid accumulation.
• Radiography: Standard overview radiographs may reveal soft tissue thickening and typical bone erosion defects (e.g., in the region of the first metatarsophalangeal joint).
• Magnetic resonance imaging (MRI): In T1 mode, it allows the true scale of the problem to be assessed. MRI visualizes multiple erosions and the true extent of tophi, which may be completely invisible on conventional radiographs.

Chronic stage: erosions and tophi

The chronic course of the disease leads to the formation of specific structural changes in the joints and soft tissues.

Gouty erosions have several distinctive features:

• Located predominantly periarticularly (around the joint).
• Formed on a broad base.
• Have well-defined, characteristic overhanging sclerotic margins.

Tophi (Tophi) are the main radiological and clinical sign of chronic gout. They appear as dense, mass-like lesions in soft tissues. Crystal deposition imparts high density to them both on radiographs and sonography. Soft tissue edema is asymmetric in nature. Crystals also actively accumulate in tendons.

Tophi are most frequently localized in the following areas:

1. Hands.
2. Wrist joints (predominantly on the ulnar side).
3. Extensor surfaces of the elbow joints.
4. Extensor surfaces of the knee joints.

Calcium pyrophosphate crystal deposition disease (CPPD)

To avoid confusion in diagnoses, it is necessary to strictly separate terms related to calcium pyrophosphate dihydrate (CPPD) crystals:

• Chondrocalcinosis (Chondrocalcinosis): The actual fact of cartilage tissue calcification visible on a radiograph or under a microscope. It can be triggered not only by CPPD but also by other calcium crystals.
• CPPD deposition disease: A specific concept for a pathology in which CPPD crystals accumulate inside joints or in periarticular tissues.
• Pseudogout (Pseudogout): An acute clinical condition. Crystals provoke an acute attack visually and symptomatically mimicking gout. It is important to remember that this is an exclusively clinical diagnosis and cannot be made solely on the basis of a radiograph.
• Pyrophosphate arthropathy: A specific pattern of joint destruction in CPPD. It closely resembles classical osteoarthritis (OA) but has its own specific features. Chondrocalcinosis on radiographs may be either present or completely absent.

Clinical features and imaging signs of CPPD

Pyrophosphate deposition disease more commonly affects elderly patients. The disease is closely associated with such conditions as osteoarthritis, haemochromatosis (haemochromatosis), and Wilson disease (Wilson disease). In 10–20% of patients, intermittent acute attacks of pseudogout are observed.

Imaging features of CPPD:

• Localization: The classic target is the hyaline and fibrocartilage of the knee and wrist joints, although any joint may be affected.
• Ultrasound appearance: Pyrophosphate crystals themselves look identical to urates in gout. However, their localization is fundamentally different—they lie strictly within the articular cartilage rather than on its surface.
• Synovial accumulations: Crystal deposits are frequently found in the synovial membrane. On radiographs, they are best sought in the suprapatellar pouch of the knee joint.
• Radiographic arthropathy: The picture mimics osteoarthritis. Joint space narrowing, pronounced cyst formation, and subchondral sclerosis are observed.

Class and exam questions

What else to study on this topic

• Features of the differential diagnosis of gout and rheumatoid arthritis on radiographs
• Principles of dual-energy CT in rheumatology: physics of the method and color-mapping
• Pyrophosphate arthropathy vs. Osteoarthritis: subtle imaging differences
• The role of ultrasound in monitoring chronic gout therapy

Other topics in the "Musculoskeletal System" section

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.