Rheumatoid arthritis = chronic systemic connective tissue disease = type III hypersensitivity = delayed hypersensitivity = immune complex disease (= formation of antigen-antibody complexes with

complement fixation) with T-cell–mediated autoreactivity against a joint componentPrevalence: 0.5-1.0% of population

Cause: genetic predisposition;? reaction to antigen from Epstein-Barr virus / certain strains of E. coli

Peak age: 45-65 years; M:F = 1:3 if <40 years; M:F = 1:1 if >40 years

Pathogenesis: o injury to synovial endothelial cells; synovitis with synovial hyperplasia

and pannus formation mediated by TNF-خ± (tumor necrosis factor خ±) and IL-1 (interleukin 1) leads to invasion by local macrophages, fibroblasts, and activated lymphocytes; invasion of articular cartilage + bone by secretion of degrading enzymes (metalloproteinases)

Diagnostic Criteria of American Rheumatism Association (at least 4 criteria should be present):

o morning stiffness for 1 hour before improvemento swelling of 3 joints, particularly of wrist, metacarpophalangeal or

proximal interphalangeal joints for >6 weekso symmetric swellingo typical radiographic changeso subcutaneous rheumatoid noduleso positive test for rheumatoid factor

rheumatoid factor (positive in 85-94%) = IgM-antibody antinuclear antibodies (positive in many)

Location:bilateral symmetric involvement of >3 diarthrodial joints (polyarthritis)

  Symmetric arthritis of multiple small hand joints in >60% of patients at initial presentation

EARLY SIGNS:

- MR&US (methods of choice):

- synovial hyperemia (in acute disease + exacerbation of chronic disease)

- synovial swelling (edema + cellular infiltrates)

- pannus = tumor like focal proliferation of inflammatory tissue with destruction of cartilage and bone

- pre-erosive subcortical cysts

- joint effusion

- bone marrow edema

* Radiography (indirect & nonspecific):

- fusiform periarticular soft-tissue swelling (result of effusion)

- paraarticular osteoporosis (inactivity due to pain + local inflammatory hyperthermia)

- translucent subchondral end plate

- widened joint space (synovial swelling + fluid)

- effacement of fat pads

- subcortical synovial cyst

- erosion (up to 47% within 1st year after onset) initially at bare area (= site of attachment of internal synovial layer of joint capsule to bone) due to lack of

protective cartilage layer

LATE SIGNS:

- concentric joint space narrowing (due to destruction of cartilage, formation of scar tissue, fibrosis)

- subluxation (due to laxity of capsule + ligaments from inflammatory destruction / due to capsular shrinkage from fibrosis + scar formation):

- mallet finger = droopy distal phalanx due to disrupted extensor tendon insertion site

- swan-neck deformity = hyperextension at PIP + flexion at DIP

- boutonniأ¨re deformity = flexion at PIP + hyperextension at DIP

- hitchhiker deformity = flexion at MCP + hyperextension at DIP

- dislocation

- marked destruction + fractures of bone ends:

- intraarticular loose bodies

- rice bodies = subset of loose bodies resembling polished rice (made of sloughed fibrinogen-coated infarcted synovial tissue / precipitate of fibrin + fibronectin /

core of mononuclear cells, blood cells and amorphous material)

-bony ankylosis

@ Hand & wrist (typical)

o Target areas: all five MCP, PIP, interphalangeal joint of thumb, all wrist

compartments (especially radiocarpal, inferior radioulnar, pisiform-triquetral joints); earliest changes seen in MCP 2 + 3, PIP 3

- marginal + central bone erosions (less common in large joints); site of first erosion is classically base of proximal phalanx of 4th finger

- changes in the ulnar styloid + distal radioulnar joint (early sign)

- flexion + extension contractures with ulnar subluxation + dislocation

@ Cervical spine

- erosions of odontoid process (1) between anterior arch of atlas + dens, (2) between transverse ligament of atlas + dens, (3) at tip of odontoid process

- anterior atlantoaxial subluxation (in >6%): >2.5 mm in adults, >4.5 mm in children during neck flexion

- cranial settling= odontoid process projects into skull base due to significant disease of atlanto-occipital and atlantoaxial joints

- lateral head tilt = lateral subluxation = asymmetry between odontoid process + lateral masses of atlas

- stepladder appearance of cervical spine due to subaxial subluxations + absence of osteophytosis:

- destruction + narrowing of disk spaces

- irregular vertebral body outlines

- erosion + destruction of zygapophyseal joints

- resorption of spinous processes

- osteoporosis

@ Ribs

- erosion of superior margins of posterior portions of ribs 3-5

@ Shoulder

- symmetric loss of glenohumeral joint space:

- marginal erosions at superolateral aspect of humeral head

- osteoporosis

- elevation of humeral heads = narrowing of acromiohumeral distance (2آ° to tear / atrophy of rotator cuff)

- widened acromioclavicular joint:

- erosions at acromial + clavicular end

- tapered margins of distal clavicle

- scalloped erosion on undersurface of distal clavicle opposite the coracoid process (attachment of coracoclavicular ligament)

@ Sacroiliac joint (rarely affected)

- typically asymmetric unilateral distribution

- shallow erosions + mild sclerosis

- rare ankylosis

@ Hip (rarely affected)

- often appears normal during early disease process

- pannus formation (MR imaging)

- symmetric loss of joint space with axial migration of femoral head

- marginal + central erosions, cysts, localized sclerosis

- decompression of joint effusion into iliopsoas bursa through weak anterior capsule displacing muscle + vasculature

- rupture of gluteal tendon

- protrusio acetabuli (from osteoporosis)

@ Knee

Location:medial + lateral femorotibial compartments; bilateral symmetric

- diffuse loss of joint space

- osteoporosis

- superficial + deep marginal + central erosions

- subchondral sclerosis (especially in tibia)

- synovial herniation + cysts (eg, popliteal cyst)

- varus / valgus angulation (due to crumbling of osteoporotic bone of tibia + ligamentous abnormalities)

@ Foot (typical) o Target areas:

medial aspect of MT heads (2,3,4), medial + lateral aspect of MT5 (earliest sign); interphalangeal joints of foot (esp. great toe); midfoot joints; talonavicular, subtalar, tarsometatarsal joints; bilateral + symmetric

- sinus tarsi syndrome = compression of tibial nerve

- calcaneal plantar spur

- retrocalcaneal bursitis

EXTRA-ARTICULAR MANIFESTATIONS (76%) o Felty syndrome (<1%)

= rheumatoid arthritis (present for >10 years) + splenomegaly + neutropenia

Age:40-70 years; F > M; rare in Blacks

o Sjogren syndrome (15%) = keratoconjunctivitis + xerostomia + rheumatoid arthritis

- Pulmonary manifestations

- pleural effusion, mostly unilateral, without change for months, usually not associated with parenchymal disease

- interstitial fibrosis with lower lobe predominance

- rheumatoid nodules (30%): well-circumscribed, peripheral, with frequent cavitation

- Caplan syndrome (= hyperimmune reactivity to silica inhalation with rapidly developing multiple pulmonary nodules)

- pulmonary hypertension secondary to arteritis

- Subcutaneous nodules

- Cardiovascular involvement

Pericarditis (20–50%) Myocarditis (arrhythmia, heart block) Aortitis (5%) of ascending aorta آ± aortic valve insufficiency

- Rheumatoid vasculitis

- Neurologic sequelae

Distal neuropathy (related to vasculitis) Nerve entrapment (atlantoaxial subluxation, carpal tunnel

syndrome, Baker cyst)

- Lymphadenopathy (up to 25%) - splenomegaly

Cystic Rheumatoid Arthritis = intraosseous cystic lesions as dominant featurePathogenesis:increased pressure in synovial space from joint effusion

decompresses through microfractures of weakened marginal cortex into subarticular bone

Increase in size + extent of cysts correlates with increased level of activity + absence of synovial cysts

Age:as above; M:F = 1:1

- juxtaarticular subcortical lytic lesions with well-defined sclerotic margins

- relative lack of cartilage loss, osteoporosis, joint disruption

DDx:

gout (presence of urate crystals), pigmented villonodular synovitis (monoarticular)

Juvenile Rheumatoid Arthritis = rheumatoid arthritis in patients <16 years of age; M < F

Location:early involvement of large joints (hips, knees, ankles, wrists, elbows); later of hands + feet

- radiologic signs similar to rheumatoid arthritis (except for involvement of large joints first, late onset of bony changes, more ankylosis, wide metaphyses)

- periarticular soft-tissue swelling

- thinning of joint cartilage

- large cystlike lesions removed from articular surface (invasion of bone by inflammatory pannus); rare in children

- articular erosions at ligamentous + tendinous insertion sites

- joint destruction may resemble neuropathic joints

- juxtaarticular osteoporosis

- balloon epiphyses + gracile bones (epiphyseal overgrowth + early fusion with bone shortening secondary to hyperemia)

- Hand / foot

o “rectangular†phalanges (periostitis + cortical thickening)o ankylosis in carpal joints

- Axial skeleton

Location:predominantly upper cervical spine

- ankylosis of cervical spine (apophyseal joints), sacroiliac joints

- decreased size of vertebral bodies + atrophic intervertebral disks

- subluxation of atlantoaxial joint (66%)

- thoracic spinal compression fractures