the swollen joint and its diagnostic workup

see also:

• osteomyelitis and septic arthritis
• rheumatoid arthritis
• rheumatology
• arthritis - clinical patterns
• assessment of joint function and arthritis severity
• extra-articular clinical features of rheumatologic conditions
• RCH guideline - the acutely swollen joint

• there are no good screening tests for rheumatic diseases, a thorough history and examination with a few basic tests should be adequate and avoid unnecessary false-positive and false-negative ramifications of inappropriate investigations.
• see arthritis - clinical patterns for the basic clinical diagnostic patterns
• see septic arthritis if you are considering septic arthritis

• erythrocyte sedimentation rate (ESR), C reactive protein (CRP):
  • non-specific tests that are sometimes helpful in distinguishing between inflammatory and non-inflammatory conditions. However, they are not diagnostic and may be abnormal in a vast array of infectious, malignant, rheumatic and other diseases. 
  • An ESR above 40 mm/h may indicate polymyalgia rheumatica or giant cell arteritis if the patient's history and physical examination are compatible with either diagnosis. Unfortunately, the ESR may be below 40 mm/h in up to 20% of patients with these conditions.
  • may be useful for monitoring patients with rheumatoid arthritis, polymyalgia rheumatica and giant cell arteritis - but other conditions may make it rise.
• anti-nuclear antibodies (ANA):
  • see anti-nuclear antibodies (ANA)
• joint aspirate looking for inflammatory cells, crystals and culture.

• see rheumatoid factor
• This test is not useful for screening. It is nonspecific and insensitive - the presence of rheumatoid factor does not indicate rheumatoid arthritis, nor does its absence rule out rheumatoid arthritis. Thus, a positive rheumatoid factor in a patient with nonspecific symptoms may precipitate unnecessary investigations.

• Serum uric acid testing is often ordered for the patient with acute monoarthritis. Unfortunately, this will not be helpful in the diagnosis because of the high prevalence of asymptomatic hyperuricemia (5-8% of adult males) and the fact that, in 10% of patients with acute gout, serum uric acid levels are normal. 
• A diagnosis of acute gout can only be made with certainty by joint aspiration to confirm the presence of urate crystals under polarized light.
• Hyperuricemia does not confer a diagnosis of gout and need not be treated unless serum uric acid levels are persistently above 760 µmol/L (12.8 mg/dL) for men or 600 µmol/L (10.0 mg/dL) for women. At these levels there is an increased risk of renal complication.

• This test should be ordered only when SLE is suspected after history and physical examinations have been carried out and an ANA test is positive
• see antibodies to double stranded DNA (dsDNA / anti-DNA)

• Complement testing is useless for screening but is often used to monitor disease activity in patients with SLE;
• Decreased levels of complement arise from immune-complex disorders such as SLE, selected forms of vasculitis (e.g., essential mixed cryoglobulinemia and rheumatoid vasculitis), certain types of glomerulonephritis and inherited complement deficiencies.
• see complement C3, C4 testing

• characteristically occur in vasculitic syndromes - occur in more than 90% of patients with systemic Wegener's granulomatosis (with renal or pulmonary involvement, or both), 75% of patients with limited Wegener's granulomatosis (without renal involvement) and 50% of patients with microscopic polyarteritis. c-ANCAs are actually antibodies to protein 3. The presence of c-ANCAs is 98% specific for these diseases; changes in c-ANCA levels often precede disease activity and may guide treatment.
• A primary care physician will rarely need to order this test; it helps in the diagnosis and management of only a very small number of patients with relatively rare conditions, and screening patients with nonspecific symptoms results in many false-positive p-ANCA results.
• see antineutrophil cytoplasmic antibodies (ANCAs)

• Human leukocyte antigen (HLA) B27 is present in the blood of 5%-8% of the general population but in 95% of white and 50% of black patients with ankylosing spondylitis.
• This antigen is also present in 50%-80% of patients with other seronegative spondyloarthropathies, such as reactive arthritis (Reiter's syndrome), psoriatic arthritis with spondylitis and spondylitis associated with inflammatory bowel disease.
• This test is of no value in diagnosing the usual patient with back pain. In addition, it does not usually need to be ordered to confirm a diagnosis of ankylosing spondylitis although, rarely, it will be helpful in diagnosing patients who have an atypical presentation of this condition.
• Testing for HLA-B27 may be useful for the patient with acute unilateral uveitis who also has inflammatory back pain but no sacroiliitis visible on plain radiographs and for young women with recent onset of inflammatory back pain with no sacroiliitis on plain radiographs. Women with ankylosing spondylitis are more likely than men to have normal plain pelvic radiographs, thereby making diagnosis more difficult.
• The routine ordering of HLA-B27 tests for patients with nonspecific low-back pain will invariably result in many false-positive results and thus, erroneous diagnoses. Because a first-degree relative of a patient with ankylosing spondylitis has only a 10%-20% chance of ever developing the disease, asymptomatic family members of a person with ankylosing spondylitis should not be tested for the presence of HLA-B27. A positive test might also limit a person's ability to obtain life or disability insurance. There are no preventative measures to introduce when an asymptomatic person has a positive test result.

• Soft tissue swelling:
  • early rheumatoid arthritis - synovitis
  • Reiter's - periostitis
  • Charcot
  • tuberculosis (TB) spine - paraspinal mass
• Erosions:
  • DDx of erosions in hands:
    • RhA: cortical erosions in MCPs, ulnar styloid, carpals
    • gout
    • psoriatic
    • sarcoidosis
    • misc: Gaucher's; Albright's; osteitis fibrosa cystica (“brown tumours”); aneurysmal bone cyst; non-ossifying fibroma;
  • Reiter's: asymmetric erosions sparing hands
  • ankylosing spondylitis (AS):
    • Romanus lesion (erosion of ant-sup vertebra); SI jt erosion; Hip jt erosions;
• Calcification:
  • chondrocalcinosis (calcification of cartilage)
  • sclerosis:
    • Charcot
    • osteoarthritis - subchondral;
    • ankylosing spondylitis (AS) - SI jt;
• Osteoporosis (juxtaarticular):
  • rheumatoid arthritis
  • NB. NONE in OA, Charcot
• Narrowing of joint space:
  • osteoarthritis
  • ankylosing spondylitis (AS):
    • SI jt fusion; apophyseal jt fusion;
  • spinal TB: narrowed disc space;
• Deformity:
  • Charcot - destructive changes, loose bodies
  • late rheumatoid arthritis - subluxation & deformity
  • osteoarthritis - osteophytes, loose bodies
  • Reiter's - calcaneal spurs
  • ankylosing spondylitis (AS) - vertebral squaring, syndesmophytes;
  • tuberculosis (TB) - vertebral collapse; Gibbus (acute anterior angulation)
  • metastatic Ca - obliteration of vertebral pedicle in PA; lytic or sclerotic lesions; vertebral collapse;
• Separation (fractures) and Subluxation:
  • rheumatoid arthritis: subluxation common MCPs, PIPs, 1st CMC;
  • osteoarthritis: subluxation 1st CMC
  • atlantoaxial instability:
    • rheumatoid arthritis, JCA, ankylosing spondylitis, trisomy 21

• high false negative rate in septic arthritis though!!
• 50% sensitivity in gonococcal;

• uric acid:
  • long, needle-like, negatively birefringent (yellow when parallel to compensator, blue when perpendicular)
• calcium pyrophosphate:
  • rhomboid, positively birefringent (blue when parallel to compensator, yellow when perpendicular)

• septic arthritis:
  • most septic joints have a white blood cell (WBC) count that exceeds 50,000/μL, with more than 75% polymorphonuclear leukocytes
  • NB. some labs report counts x 10^6/L which is eq. to counts/μL
  • usually > 50,000 WBC/cu.mm but early or in partially treated may be much lower
  • high WBC counts > 50,000 can occur in RhA, gout, pseudogout

• normally 95% of serum glucose
• very low in septic arthritis ⇒ may help differentiate from gout but not from RhA where glucose may also be very low

• OA, post-traumatic; sympathetic (eg. adjacent osteomyelitis); myxoedema; amyloidosis; HbS; HPOA;

• haemophilia
• intra-articular fracture
• minor trauma in anticoagulated pt
• joint tumours (incl. pigmented villonodular synovitis)
• Charcot joint; arthritis mutilans;
• calcium pyrophosphate deposition disease
• traumatic tap - centrifuge & demonstrate absent xanthochromia