Bone Erosions:
- Due to proliferative synovium
- Definition on MRI: Sharply marginated bone lesion,
juxtaarticular in location and with evidence of a cortical break seen on at least one plane
- Early erosions will be seen at the bare areas of the joint,
that is the intra-articular portion which is not covered by articular cartilage
- While RA is a bilateral symmetric disease,
erosions are less commonly bilateral compared with synovitis and tenosynovitis
- Commonly involved bones include:
- Radial aspect of 2nd and 3rd metacarpal bones
- Lateral aspect of 5th metatarsal bone
- Capitate,
triquetrum,
lunate bones
- MRI Findings
- Loss of normal signal intensity on T1 weighted images
- Hyperintense signal on T2 weighted images
- Enhancement on post contrast imaging
- Figures 1 through 10 demontrate characteristic erosions associated with RA
Pannus & Synovitis:
- Pannus is essentially a proliferative synovitis and is the earliest pathologic abnormality seen in RA
- Typically bilateral
- MRI Definition: An area within the synovial compartment demonstrating greater than average post-gadolinium enhancement with thickness of the synovium greater than normal
- Figures 11 through 18 demontrate findings of pannus and synovitis
Marrow Edema:
- Has been shown to precede the development of bone erosions
- MRI Definition: Lesion within the trabecular bone with ill defined margins,
near its insertion on the synovial membrane
- Can occur alone or adjacent to bone erosions
- Figure 19 demonstrates marrow edema in the setting of RA
Rice Bodies:
- Nonspecific response to chronic synovial inflammation
- Initially described in tuberculous arthritis
- Pathogenesis unclear although it may be related to microinfarction of the synovium with release of tissue into the joint or detachment of hypertrophied synovium
- Figures 20 and 21 demonstrate rice bodies in the setting of RA
Tenosynovitis:
- Commonly seen in RA and usually bilateral
- Any tendon can be involved although commonly seen in
- Manifested by thickening of the synovium with marked enhancement on post-gadolinium imaging
- Figures 22 to 27 show a variety of different manifestations of tenosynovitis in the setting of RA
Bursitis:
- Common finding although many patients may be asymptomatic
- In the feet it is typically seen between or beneath metatarsal heads,
commonly in second or third intermetatarsal web spaces:
- May be difficult to differentiate from a Morton’s neuroma
- Shows enhancement on post-contrast imaging
- Manifested by thickening of the synovium with marked enhancement on post-gadolinium imaging
- Figures 28 and 29 demonstrate two different types of bursitis associated with RA
Effusion:
- Increased fluid within the synovial compartment of a joint
- Commonly seen in conjunction with soft tissue edema and tenosynovitis
- Can be distinguished from synovitis on MRI due to lack of enhancement on post-gadolinium imaging
- Figures 30 and 31 demonstrate two effusions associated with RA
Differential Diagnosis:
- Osteoarthritis (OA)
- Typically involves proximal and distal interphalangeal joints (PIP and DIP)
- Characterized by osteophyte formation
- Erosive Osteoarthritis
- Central erosions are a hallmark resulting in “gull-wing” appearance,
as opposed to marginal erosions in RA
- Typically occurs in an OA distribution with marginal osteophytes and erosions at the DIP and PIP joints
- Psoriatic Arthritis
- Soft tissue edema of a digit (“sausage digit”)
- Fluffy periostitis is seen
- Characterized by bone proliferation and erosions,
whereas RA is a purely erosive disease
- Favors DIP joints although may involve others
A Look to the Future:
- MRI has been shown to demonstrate changes of RA earlier compared to radiographs
- The impact of MR imaging in RA in the future will hopefully be related to its predictive benefits and ability to monitor and gauge treatment response and effectiveness
- The ability to measure synovial volume may help determine the efficacy of therapies designed to decrease the rate of structural damage
- Many rheumatologists believe that synovitis is the main abnormality in RA,
and therefore measuring synovial volume may prove beneficial as a long-term clinical endpoint
- Sonography is increasingly being utilized in the management of RA,
specifically in evaluating cartilage damage,
bone erosions and synovitis
- Visualization of synovial microvascular blood flow as a sign of inflammation by ultrasound has become an important tool to monitor disease progression
- The development of biological therapies for the treatment of RA has introduced the exciting possibility of utilizing this technology in imaging
- Several monoclonal antibodies and their fragments,
including anti-TNF-alpha,
anti-CD20,
anti-CD3,
anti-CD4 and anti-E-selectin antibody,
have been radiolabelled mainly with (99m)Tc or (111)In
- Scintigraphy with these radiolabelled antibodies may allow for:
- Better staging of the disease and diagnosis of the state of activity by early detection of inflamed joints that might be difficult to assess clinically
- The possibility to perform evidence-based biological therapy to identify whether an antibody will localize to the site of RA before using the same unlabelled antibody therapeutically
- This may have both clinical and economic implications as biological therapies can be associated with severe side-effects and are considerably expensive