UW MSK Resident Projects
University of Washington, UWMC Roosevelt Clinic, Musculoskeletal Radiology



Psoriatic Arthritis

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Posted by klinnau@u.washington.edu, 10/16/03 at 9:16:58 AM.

Psoriatic arthritis (PsA)

  • 2-17% of patients with psoriasis get arthritis
  • skin lesions and arthritis are often asynchronous: 80-85% of pts have skin lesions first
  • synovial inflammation leading to bony proliferation at joint margins
  • inflammation at the ligamentous attachments: enthesopathy

Age of onset usually 30-45 years, no gender preference

Prognostic factors:

poor prognosis:

  • late age of onset
  • five or more effused joints
  • high immunosuppressive medication use

good prognosis:

  • ESR < 15 mm/h

other labs:

  • HLA B27 positive in 60-80% of psoriatic spondylitis and 20% of peripheral PsA
  • CRP - usually elevated
  • may be elevated: acute serum amyloid A (A-SAA)
  • ANA may be mildly elevated
  • Rheumatoid factor negative (or mildly elevated with titer<1/40, which is cut-off for Rheumatoid Arthritis (RA))


Joint damage occurs maximally during first 2 years of disease:

early diagnosis

aggressive treatment

Patterns of presentation:

  1. asymmetric oligoarthritis: > 50%
  2. polyarthiritis with predominantly DIP involvement (classic): 5-19%
  3. symmetric seronegative polyarthritis simulating RA: up to 25%
  4. sacroiliitis and spondylitis resembling Ankylosing Spondylitis (AS): 20-40%
  5. arthiritis mutilans with resorption of the phalanges: 5%


Onset may be

insidious (66%) or

acute (33%) mimicking gout or septic arthritis


Radiology findings:

Early findings:

  • normal
  • soft tissue swelling: sausage fingers or fusiform swelling about finger joint
  • usually no osteoporosis (˙≠ RA)
  • prominent erosions in marginal areas of joints
  • Perisostitis in metaphysis and diaphysis
  • asymmetric paravertebral ossification of thoraco- lumbar junction (from vertebral body to body  ˙≠  AS: corner to corner)
  • bone scans may show hot spots prior to radiographic abnormality

Distribution of radiographic findings:

  • synovial or cartilaginous joints and tendon attachment of axial and appendicular skeleton (= Reiter = AS ˙≠ RA)
  • unilateral or asymmetric (˙≠ RA) at the hands and feet
  • upper and lower extremity joints (˙≠ Reiter: more commonly lower extremity only)
  • DIP, PIP of hand and foot commonly affected
  • Abnormal phalangeal tufts and calcaneus (characteristic)
  • If axial skeleton: most commonly sacroiliac (SI) and spinal joints

General findings:

  • Soft tissue swelling
  • No osteopenia (˙≠ RA)
  • Joint space may be widened or narrowed
  • Severe marginal erosions gnawing away bone towards the center of the joint are typical
  • Pencil-and-cup appearance of small joints of hand and feet (DDX: RA, leprosy, sarcoid)
  • Bone proliferation (=other seronegative spondylarthropathies = gout): spiculated, frayed, paintbrush appearance (˙≠ RA: no bone deposition)
  • Perisostitis in metaphysis and diaphysis (= Reiter= Juvenile RA =infection) sometimes accompanied by condensation of bone
  • Intraarticular osseous fusion ( AKA bone anklylosis) (DDX: erosive OA, RA (carpus and tarsus), infection, other seronegative spondylarthropathies)
  • Enthesopathy of calcaneus (Achilles tendon), femoral trochanters, ischial tuberosities, malleoli, olecranon, patella, femoral condyles.
  • Tuft resorption of the distal phalanges of the hands and feet (characteristic) (DDX: scleroderma, thermal injury)


  • Start at joint margins, tend to be severe
  • Proceed centrally into joint
  • Result in irregular osseous surfaces: lack of apposition of adjacent bone margins (˙≠ OA)
  • Wrist abnormalities not so common in psoriasis


  • Erosion and proliferation of posterior or inferior surface
  • Radiodense area postero-inferior due to retrocalcaneal bursitis
  • Achilles tendon may be thickened.

SI joints:

  • 30-50% of patients with PsA
  • erosions and sclerosis of SI joints
  • bilateral lesions are more common than unilateral


  • asymmetric paravertebral ossification of lower thoraco- lumbar junction (from vertebral body to body  ˙≠ AS: corner to corner)
  • Syndesmophytes are greater in size, asymmetric distribution, away form vertebral column  ˙≠ AS
  • squaring of vertebral bodies, apophyseal sclerosis uncommon  ˙≠ AS
  • Cspine abnormalities may be extensive: facets, discovertebral, proliferations along anterior surface, atlantoaxial subluxation, dens erosions.


  •  bone scans may show abnormality prior to radiographs
  • asymmetric  ˙≠ RA
  • DIP, PIP >> SI, calcaneus


Lumbar spine showing bilateral sacroiliitis

Psoriatic arthritis with proliferative osteophyte on heel

T1-weighted sagittal MR of psoriatic involvement of retrocalcaneal bursa and distal Achilles tendon

T1-weighted sagittal MR of psoriatic involvement of retrocalcaneal bursa and distal Achilles tendon

Radionuclide bone scan in a patient with psoriatic arthritis and a swollen 5th finger. This delayed image shows markedly increased uptake in the 5th finger.

Hand film from same patient shows swollen 5th digit from psoriatic arthritis.

Detail view of 5th finger from same patient shows erosions from psoriatic arthritis.


This page was last updated: Thursday, August 4, 2005 at 11:45:44 AM
Copyright 2005 UW MSK Resident Projects
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