Medical Imaging for Diagnosing RA
The American College of Rheumatology (ACR) diagnostic criteria incorporate four main areas – joint involvement, RA related blood tests, general inflammation blood tests, and duration of symptoms.1 According the ACR,
“Joint involvement refers to any swollen or tender joint on examination, which may be confirmed by imaging evidence of synovitis.”2
Physical examination is the starting point for identifying joint involvement. But confirmation by actually looking inside the joint with imaging techniques remains a critical part of confirmation. The synovium is a sac-like lining around certain joints. It provides nutrients and lubrication for joint soft tissues. During the disease processes involved with RA, the synovium swells and thickens, becoming permeated with inflammatory cells and chemicals. Ultimately, cartilage and bone tissue erodes leading to the classic joint damage associated with RA.3 The synovial fluid can be taken from a joint and analyzed for chemicals and cells associated with RA.4 This can be done via needle biopsy or surgery. During an ankle surgery I had several years ago, the orthopedic surgeon sent a sample of tissue to a laboratory for analysis – the results came back positive for RA related synovitis. But no one wants to be poked or have surgery to determine if a joint is being impacted by RA. Medical imaging procedures can be used in as a noninvasive technique for examining a joint.
There are several forms of medical imaging used to examine synovitis in rheumatoid arthritis. According to the Hospital for Special Surgery, x-rays, MRIs, CT scans, and ultrasound images all serve a purpose for diagnosing the disease.5
X-rays have been used for years to examine arthritic joints. They are able to help doctors identify evidence of soft tissue swelling, joint space narrowing – a sign of cartilage destruction, and bone erosion around the margins of bones.6 When I was first getting diagnosed, an x-ray of my fingers showed erosion in the proximal interphalangeal (PIP) or middle joints delivering evidence that RA could be the culprit. Follow-up x-rays may be used to track changes in joints over time. But x-rays may not be able to show early disease activity.7 Compared to other newer imaging technologies, x-rays are not always able to reveal subtle changes. X-rays are relatively inexpensive and they can be done quickly with little inconvenience to patients. They do contribute small doses of radiation. More specialized imaging techniques are now available.
Magnetic resonance imaging, or MRI, uses powerful magnetic pulses to provide very detailed images of internal body structures and tissues.8 The sensitively of MRIs allows doctors to identify subclinical evidence of RA including subtle changes in joint tissues.9 Researchers recently demonstrated that MRI findings could improve RA diagnosis.10 MRIs are quite expensive compared to x-rays and ultrasound.
Computerized tomography, or CT scan, consists of a series of x-rays taken from various angles that are combined to create a 3D image.11 CT scans are also able to provide very detailed images of tissues. But CT scans are not routinely used for RA diagnosis and tend to more applicable to spine joints.12 It is generally recommended that the use of CT scans be limited during a given time period since they contribute substantial doses of ionizing radiation although there remains debate about the long term impacts.13
Ultrasound uses high frequency sound waves to develop images of tissues.14 Such images are beneficial for identifying soft tissue damage in a joint.15 They may also be used to guide steroid injections.16
If you have RA, you’ll likely experience many of these imaging tests throughout your life since they are a regular part of the procedures used to diagnosis and determine treatment effectiveness.
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