Rheumatoid arthritis (musculoskeletal manifestations)

Rheumatoid arthritis (RA) is a chronic multi-system disease with predominant musculoskeletal manifestations. Being a disease that primarily attacks synovial tissues, RA affects synovial joints, tendons, and bursae.

Refer to the related articles for a general discussion of rheumatoid arthritis and for the particular discussion of its respiratory manifestations.

Radiographic features

Regarding disease detection, as the early RA manifestations are non-osseous in nature, ultrasound and MRI have shown to be superior to radiographs and CT. Plain radiography, however, remains the mainstay of imaging in the diagnosis and follow-up of RA .

Plain radiograph

One large cohort study showed that radiographically demonstrable erosions were present in 30% of patients at diagnosis, and in 70% three years later .

The radiographic hallmarks of rheumatoid arthritis are:

• erosions; important early finding, in the “bare areas”, frequently in the radial side of the metacarpophalangeal (MCP) joints
• soft tissue swelling
  • fusiform and periarticular; it represents a combination of joint effusion, edema and tenosynovitis 
  • this can be an early/only radiographic finding
• osteoporosis: initially juxta-articular, and later generalized; compounded by corticosteroid therapy and disuse
• joint space narrowing: symmetrical or concentric

Hands and wrists

Diagnosis and follow-up of patients with RA commonly involve imaging of the hands and wrists. The disease tends to affect the proximal joints in a bilaterally symmetrical distribution.

RA is a synovial based process, with a predilection for:

• PIP and MCP joints (especially 2 and 3 MCP)
• ulnar styloid
• triquetrum

As a rule, the DIP joints are spared.

Late changes include:

• subchondral cyst formation: the destruction of cartilage presses synovial fluid into the bone
• subluxation causing:
  • ulnar deviation of the MCP joints
  • boutonniere and swan neck deformities
• hitchhiker’s thumb deformity
• carpal instability: scapholunate dissociation, ulnar translocation
• ankylosis
• scallop sign: erosion of the ulnar aspect of the distal radius which may be predictive of extensor tendon rupture (Vaughan-Jackson syndrome)

Elbow

• joint effusion (elevated fat pads) 
• joint space narrowing
• periarticular erosions 
• cystic changes

Feet

• similar to the hands, there is a predilection for the PIP and MTP joints (especially 4and 5 MTP)
• involvement of subtalar joint
• posterior calcaneal tubercle erosion
• hammertoe deformity
• hallux valgus

Shoulder

• erosion of the distal clavicle
• marginal erosions of the humeral head: the superolateral aspect is a typical location
• reduction in the acromiohumeral distance: "high-riding shoulder" due to subacromial-subdeltoid bursitis and high incidence of rotator cuff tear

Hip

• concentric loss of joint space, compared with osteoarthritis (OA) where there is a tendency for superior loss of joint space
• acetabular protrusio

Knee

• joint effusion
• typically involves the lateral or non-weight bearing portion of the joint
• loss of joint space involving all three compartments
• lack of subchondral sclerosis and osteophytes, compared with OA
• prepatellar bursitis

Spine

The cervical spine is frequently involved in RA (in approximately 50% of patients), whereas thoracic and lumbar involvement is rare. Findings include:

• erosion of the dens
• atlantoaxial subluxation
  • atlantoaxial distance is more than 3 mm on a flexion radiograph
• atlantoaxial impaction (cranial settling): cephalad migration of C2
• erosion and fusion of uncovertebral (apophyseal joints ) and facet joints
• osteoporosis and osteoporotic fractures
• erosion of spinous processes

Ultrasound

Sonography can assess the soft tissue manifestations of RA. In particular:

• synovial proliferation and inflammation of the superficial joints
• tenosynovitis: extensor carpi ulnaris tendon involvement is common in early disease and may lead to erosion of the ulnar styloid
• bursitis

Ultrasound also has a role in guiding corticosteroid injections in this setting.

CT

CT is not routinely used in the evaluation of peripheral RA. It has applications in imaging of the spine, and peri-operative assessment .

MRI

MRI is particularly sensitive to the early and subtle features of RA.

Commonly used sequences include T1-weighted contrast-enhanced spin-echo with fat saturation and T2-weighted spin-echo or gradient-echo sequences .

Features of RA best demonstrated with MRI include :

• synovial hyperemia: an indication of acute inflammation
• synovial hyperplasia (rice bodies)
• pannus formation
• decreased thickness of cartilage
• subchondral cysts and erosions:
  • MRI is much more sensitive than radiography
  • it is thought that subchondral cysts in RA eventually progress to erosions (i.e. constitute "pre-erosions")
  • contrast enhancement may distinguish erosions or pre-erosions from degenerative subchondral cysts
• juxta-articular bone marrow edema
• joint effusions

Differential diagnosis

The differential for the skeletal manifestations of RA includes:

• degenerative osteoarthritis
  • involves the: DIPs, PIPs, 1CMC joints
  • non-uniform joint space loss, subchondral sclerosis, and osteophytes
  • soft tissue swelling: Heberden node (DIPs) and Bouchard node (PIPs)
  • no erosions and no ankylosis
• erosive osteoarthritis
  • clinically acute inflammatory attacks (swelling, erythema, pain) in postmenopausal women
  • typically involves the DIPs, PIPs, 1CMC joint , but not MCP joints or large joints
  • classic central erosions, possible ankylosis
• psoriatic arthritis (PsA)
  • commonly involves the hands and there is an interphalangeal predominant distribution in PsA compared to MCP joint predominance in rheumatoid arthritis (RA)
  • starts with erosions in the margins and eventually involves the
    whole joint, the classic changes being the pencil-in-cup deformity and bone proliferation (unlike RA)
  • osteoporosis not a feature in PsA
  • MRI dynamic enhancement pattern may differentiate PsA from RA at 15 minutes
• reactive arthritis (Reiter syndrome)
  • a predilection for the lower limb
  • osteopenia and then osteoporosis, uniform joint space loss, subchondral cyst formation, subluxations, marginal erosions but no bone formation
  • symmetrical involvement of the: PIPs, MCPs, and carpal bones
• systemic lupus erythematosus (SLE)/Jaccoud arthropathy
  • joint space loss, subchondral sclerosis, osteophyte, and ulnar deviation of the phalanges without erosions
• calcium pyrophosphate dihydrate (CPPD) arthropathy
  • usually only affects the MCPs: symmetric joint space narrowing, subchondral cysts, and osteophytes
  • unlike RA: chondrocalcinosis and no erosions 
• gout
  • usually in older men
  • punched out erosions usually with a sclerotic border and overhanging edges, tophi most commonly involves the 1 MTP (which is known as podagra)

Site-specific differential diagnosis:

• distal clavicular erosion
• erosion of the odontoid process