What are the common CT findings in Rheumatoid Arthritis (RA)?

CT Findings in Rheumatoid Arthritis

CT is more sensitive in detecting erosions compared to radiography and MRI in rheumatoid arthritis, though it is not routinely used due to its limited ability to show synovial hypertrophy and other soft tissue abnormalities. 1

Osseous Findings on CT

• Erosions are more readily detected on CT compared to conventional radiography, with CT showing 19% sensitivity, 100% specificity, and 81% accuracy in diagnosing erosions of the metacarpophalangeal joints when using CT as the reference standard 1
• CT can demonstrate cortical bone abnormalities with high precision, making it excellent for characterizing erosive changes 1
• Periarticular osteopenia, a hallmark of RA, can be visualized on CT but is better appreciated on conventional radiography 1
• Uniform joint space narrowing is visible on CT and represents cartilage loss 1
• Bone proliferation at sites of enthesitis can be demonstrated on CT in patients with RA 1

Soft Tissue Findings on CT

• CT has limited ability to demonstrate synovial hypertrophy compared to MRI and ultrasound 1
• Soft tissue tophi (in cases where RA coexists with gout) may appear as areas of increased attenuation on routine CT 1
• Tendon and ligament calcifications can be visualized on CT, though these are more common in crystal deposition diseases than in uncomplicated RA 1

Advanced CT Applications

• Dual-energy CT has been used primarily for detecting monosodium urate crystals in gout with high sensitivity and accuracy, but is not routinely used for RA evaluation 1
• Tomosynthesis, a technique similar to conventional tomography, can show more erosions than routine radiography and may be an alternative to CT in some settings 1
• When combined with single-photon emission CT (SPECT), CT can help differentiate RA from osteoarthritis by providing additional tomographic information 1

Clinical Utility of CT in RA

• Despite its superior ability to detect erosions, CT is not routinely used in clinical practice for RA evaluation 1
• CT is limited in its ability to show active inflammation, which is better assessed with MRI (which can show bone marrow edema and synovitis) or ultrasound (which can show synovial hyperemia) 1, 2
• The American College of Rheumatology does not recommend CT as a first-line imaging modality for RA diagnosis or monitoring 2

Comparison with Other Imaging Modalities

• Conventional radiography remains the initial imaging method of choice for detecting damage in RA, showing periarticular osteopenia, uniform joint space narrowing, and osseous erosions 1, 2
• MRI is more sensitive than CT for detecting early inflammatory changes and has higher diagnostic performance in early stages of RA 1
• Ultrasound outperforms clinical evaluation in detecting inflammation and structural damage of RA and provides prognostic information 1
• FDG-PET/CT is not routinely used in the evaluation of RA, though it can detect inflammation at sites of disease activity 1

Common Pitfalls and Caveats

• CT exposes patients to ionizing radiation, which limits its use for routine monitoring of RA progression 1
• CT findings alone cannot distinguish active from inactive disease, as structural damage may persist after inflammation has resolved 1
• Erosions detected on CT may not always correlate with functional impairment, as recent evidence suggests joint space narrowing (cartilage damage) may be more closely related to functional status than erosions 3
• The presence of large geodes (subchondral cysts) on CT may present diagnostic challenges, as these are less common in typical RA but can occur in advanced disease 4