Investigations
1st investigations to order
plain film x-rays of the hands and feet
Test
Early psoriatic arthritis (PsA) may not have classical radiographic changes.
Patients with clinical evidence of joint inflammation should have plain film radiographs of the hands and feet since 40% of patients with PsA may have radiographic damage.[43]
Erosion in the DIP joint is characteristic, as is periarticular new-bone formation of fluffy periostitis. The classic changes of osteolysis leading to arthritis mutilans or pencil-in-cup deformity are observed only in advanced established disease.
Soft-tissue swelling may be the only radiographic finding seen in early disease.
Unlike rheumatoid arthritis (RA), periarticular osteopenia is not a manifestation of early PsA. Erosions are seen in less than a quarter of early disease cases.
Result
erosion in the distal interphalangeal (DIP) joint and periarticular new-bone formation; osteolysis and pencil-in-cup deformity in advanced disease
erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP)
Test
Acute phase reactants are elevated in around 40% of patients.[9]
A high ESR or CRP is associated with polyarticular and progressive arthritis.
Result
normal or elevated
rheumatoid factor
Test
This is a non-specific test and can be positive in people without rheumatoid arthritis (RA). A negative result may be of use in distinguishing psoriatic arthritis from RA.
Result
negative in most patients
anti-cyclic citrullinated peptide (anti-CCP) antibody
Test
A highly specific test for rheumatoid arthritis (RA). However, it may be present in a small number of patients with established polyarticular psoriatic arthritis. In patients presenting with oligoarticular disease, a negative anti-CCP antibody test is useful for excluding RA.[53]
Result
mostly negative
lipid profile
Test
Because of the increased risk of metabolic syndrome in psoriatic disease, patients should have the appropriate metabolic screening, including a lipid profile.
Result
normal or hyperlipidaemia
fasting blood glucose
Test
Because of the increased risk of metabolic syndrome in psoriatic disease, patients should have the appropriate metabolic screening, including fasting blood glucose.
Result
normal or hyperglycaemia
uric acid level
Test
Because of the increased risk of metabolic syndrome in psoriatic disease, patients should have the appropriate metabolic screening, including a uric acid level.
Result
normal or elevated
synovial fluid aspiration and analysis
Test
Synovial fluid examination may be necessary in monoarthritis to exclude gout or infection.
Result
absence of monosodium urate crystals
Investigations to consider
plain film x-rays of the spine and pelvis
Test
Between 25% and 33% of patients with psoriatic arthritis (PsA) have isolated spondylitis without sacroiliitis.[47][48] Asymmetrical sacroiliitis is characteristic of PsA and may be asymptomatic. X-ray findings in early disease are usually normal; however, radiographic changes in advanced disease can help support the diagnosis. Therefore, plain film x-rays of the spine and pelvis are indicated in patients with symptoms or physical findings suggestive of hip, sacroiliac, or spine involvement.
Result
normal in early disease; unilateral sacroiliitis and syndesmophytes (predominantly in the cervical spine) observed with advanced disease
MRI scan of sacroiliac joints
Test
Although not routinely indicated, an MRI scan of the sacroiliac joints may be of use in identifying those patients suspected of having early sacroiliitis despite absence of radiographic changes.[4] Abnormal findings can occur in asymptomatic patients.
Result
subchondral bone oedema is characteristically observed
Emerging tests
joint ultrasound
Test
Currently a clinical research technique used to demonstrate the extent of entheseal involvement in psoriatic disease.
Result
swelling of the tendon, erosion at the insertion site, and increased vascularity
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