4 Imaging Studies Used for Rheumatoid Arthritis

Common Imaging Modalities Help Assess Rheumatic Disease

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Diagnosing rheumatoid arthritis typically involves a physical examination performed by a rheumatologist, blood tests, and imaging studies. The imaging studies may include plain radiography (more commonly referred to as x-ray), CT scan (computed tomography), MRI (magnetic resonance imaging), or ultrasonography. In rheumatology, imaging studies help establish or confirm the diagnosis, determine the extent of the disease, and monitor structural changes as the disease progresses.

Plain Radiography (X-ray)

Plain radiograph, or x-ray, is usually the starting point when imaging studies are used to evaluate suspected rheumatic diseases. A plain x-ray is a two-dimensional image that is formed by the variable absorption of x-rays by tissues of the body. 

With high spatial resolution (i.e., higher pixel count), x-rays provide good visualization of features associated with rheumatoid arthritis. Early in the course of the disease, plain x-rays may appear normal, but over time there often is evidence of subtle changes that may later progress to severe joint damage.

Typically, the earliest evidence on plain x-rays, which can occur within weeks of rheumatoid arthritis onset, includes soft tissue swelling and periarticular osteoporosis (loss of bone density around the joints). Periarticular osteoporosis is caused by inflammation. Within months, there may be evidence of bone erosion around the joints, caused by invasive and destructive synovial pannus.

In early rheumatoid arthritis, evidence of bone erosion is usually first seen in specific joints of the hands (MCP and PIP joints) and feet (MTP joints). There also can be evidence of cartilage loss and joint space narrowing on plain x-ray.

In advanced cases, the progression of rheumatoid arthritis can worsen to the point of complete cartilage destruction.

When that occurs, the ends of two bones may fuse (referred to as ankylosis) or rub against each other (bone-on-bone). 

The negative aspect of plain x-ray is that it has low sensitivity and specificity for soft tissue abnormalities. CT or MRI can provide greater detail for soft tissue changes.

CT Scan or Computed Tomography

CT is a tomographic radiographic imaging technique that can visualize calcified tissue with high resolution. Tomography, which uses ionizing radiation, is an imaging technique that produces an x-ray photograph of a selected plane section of the human body. In rheumatology, CT is used to detect abnormalities in the axial skeleton (i.e., the head and trunk). For example, CT can detect erosion, sclerosis, fracture, and new bone formation.

With CT, spatial resolution is high and contrast resolution between soft tissue and bone is the best of any imaging modality. But, CT scan still does not offer sufficient soft tissue contrast for it to be widely used. It also is more expensive than plain x-ray.

MRI

MRI provides multiplanar tomographic imaging with superior contrast for soft tissues, without using ionizing radiation. MRI can help assess all structures involved in musculoskeletal disease.

While MRI has the potential for revealing erosions before they are evident on plain x-ray and can provide greater details of the joint and surrounding joint structures, as well as bone marrow lesions,  it is not routinely used for diagnosing rheumatoid arthritis. The use of MRI has increased, but it is still considered more costly, and there is not a clear-cut need for the additional detail it provides as it relates to diagnosis or prognosis. There is also some question about the correlation between MRI findings and actual clinical symptoms.  

Ultrasonography

Ultrasonography creates images based on the location of acoustic interfaces in tissue as a transducer is applied to the section of body being examined. Ultrasonography, which uses no radiation, can detect various abnormalities associated with rheumatoid arthritis, including joint space narrowing, synovial abnormalities, cartilage defects, intra-articular fluid accumulation, bone erosions, tendon sheath widening, and tendon tears. Disease activity within the synovium can be assessed using power color Doppler technology.

Ultrasonography has high spatial resolution making it possible to detect minimal bone erosions. For detecting bony erosions, ultrasonography has higher sensitivity than plain radiograph and it is comparable to MRI.

Resolution is higher, though, for body tissues that are superficial rather than deeper (i.e., finger versus hip). That's one consideration for determining the usefulness of ultrasonography. Other considerations include the availability of the equipment, as well as competence of the operator.

Sources:

Rheumatoid Arthritis: Early Diagnosis and Treatment. Cush, Weinblatt, and Kavanaugh. Third edition. Imaging Studies. Chapter 5. Page 71. Professional Communications, Inc.

Rheumatoid Arthritis. Oxford Rheumatology Library. Luqmani, Pincus, and Boers. Imaging of Joints. Chapter 3.5. Oxford University Press.

Primer on the Rheumatic Diseases. Thirteenth edition. Chapter 2. Imaging of Rheumatologic Diseases. Scott, Didie, and Fayad.

Kelley's Textbook of Rheumatology. Ninth edition. Imaging Modalities in Rheumatic Diseases. Chapter 58. Ostergaard, Lambert, and Grassi

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