Radiography

Regardless of the rheumatoid serology, the joint inflammations can be characterized radiographically by three main phenomena, which unspecifically represent the inflammatory pathomorphological processes of the joint:

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  Soft-tissue signs of arthritis correspond to the swelling of articular and periarticular tissues, such as the synovium, the joint capsule, and their surroundings. Widening of the joint space caused by effusion or synovitic swelling can be seen in children and also in the hand and finger joints of adults.

  
  
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  Collateral signs of arthritis represent periarticular demineralization of the subchondral and metaphyseal bone. They can be triggered by inflammatory circulatory disturbances, altered osteoblastic function, immobilization, and prostaglandins.

  
  
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  Direct signs of arthritis are direct or indirect results of the destructive effect of inflammatory exudation and proliferation of the synovial membrane on bones and cartilage ( Table 37.3 ).

Table 37.4 differentiates seronegative spondylarthritis from rheumatoid arthritis. Four characteristics are useful in the differential diagnosis of seronegative polyarthritis:

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  Asymmetric distribution pattern

  
  
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  Lack of periarticular osteopenia

  
  
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  Bone proliferation

  
  
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  Bony ankylosis

Nuclear Medicine

Various techniques are available:

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  Three-phase skeletal scintigraphy with ^99mTc phosphonates detects inflammatory soft-tissue reactions and osseous lesions at a very early stage. When several foci are located, the disease pattern can be defined (Fig. 37.1d) Follow-up examinations during therapy are controversial because they often do not provide any additional information to the clinical findings.

  
  
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  Joint scintigraphy with Tc-pertechnetate is rarely indicated. This radiopharmacologic agent accumulates only in the inflamed synovium and synovial fluid. Arthritic manifestation in the hand and fingers can be seen without overlapping, particularly in children.

  
  
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  Inflammation scintigraphy with ^99mTc-HMPAO-labeled autologous leukocytes and Tc-nanocolloid, as well as immunoscintigraphy with ^99mTc-labeled murine monoclonal granulocytes or human unspecific immunoglobulin, sensitively identify granulocyte-induced inflammations. Aseptic or chronic arthritides are generally not marked.

Ultrasonography

Differentiation between periarticular soft-tissue edema and effusions in joints and tendon sheaths (Chapter 7) can be achieved with a high-frequency probe(7.5 MHz and higher) using a water coupling.

Computed Tomography

In addition to differentiating pathologic soft-tissue swellings, CT imaging can also detect early erosions on the subchondral bone plate. A high-resolution reconstruction algorithm must be used. CT is superior to MRI in visualizing the bone structure. It is recommended to perform axial slices in the carpal area and longitudinal slices in the fingers. Puncture can be accurately guided with CT and ultrasonography (US).

Magnetic Resonance Imaging

MRI is the method of choice to detect the early stages of intra- and extraarticular inflammation and the initial involvement of the bone marrow because of its superior differentiation of soft tissues. It provides a detailed view of the small joints, including cartilage, synovium (pannus), joint capsules, tendons, and bone marrow. Fat-suppressed T2-weighted sequences sensitively record edema in the bone marrow and soft tissues, as well as minimal effusions. Gadolinium dye should always be administered intravenously in patients with arthritic diseases because hyperemic lesions can be clearly detected and localized by their massive enhancement. Coronal slices in T1- and T2-weighted sequences are the procedures for standard orientation.

Disease Entities

Radiography

The characteristic pattern of distribution on the hand ( Table 37.1 ) and the combination of osteoproliferative and osteodestructive lesions ( Table 37.5 , Fig. 37.2 –37.4 and 37.5 ) are useful for differential diagnosis. Involvement of bone sections and soft tissues far from joints leads to the typical appearance of psoriatic dactylitis.

On the foot, psoriatic arthritis is manifested by erosive defects on the interphalangeal and metatarsophalangeal joints, as well as fibro-ostitis on the calcaneus in the insertion of the Achilles tendon and the plantar aponeurosis. A fairly asymmetric sacroiliitis is found in 30–50% of cases. Psoriatic spondylitis is characterized characterized by asymmetric parasyndesmophytes-paradiscal, lumpy new bone formations to be differentiated from the syndesmophytes of ankylosing spondylitis. Involvement of the medium-sized and large joints is rarer and radiomorphologically comparable to rheumatoid arthritis.