eMedicine Specialties > Rheumatology > Spondyloarthropathies

Psoriatic Arthritis: Differential Diagnoses & Workup

Author: Anwar Al Hammadi, MD, FRCPC, Consultant Dermatologist, Assistant Clinical Professor of Dermatology, University of Sharjah, Dubai, United Arab Emirates
Contributor Information and Disclosures

Updated: Apr 29, 2009

Differential Diagnoses

Gout
Osteoarthritis
Reactive Arthritis
Rheumatoid Arthritis
Septic Arthritis

Other Problems to Be Considered

Psoriasiform skin lesions may be observed in association with Reiter disease, inflammatory bowel disease, and the syndrome of inappropriate secretion of diuretic hormone.

Workup

Laboratory Studies

  • No specific diagnostic tests are available for psoriatic arthritis. Diagnosis of the disease is made based on clinical and radiologic criteria in a patient with psoriasis.  
    • The most characteristic laboratory abnormalities in patients with psoriatic arthritis are elevations of the erythrocyte sedimentation rate (ESR) and C-reactive protein level. The results from these laboratory tests help track the activity of the disease by measuring inflammation. An elevated ESR is usually found in approximately 40% of patients with psoriatic arthritis.
    • Patients with psoriatic arthritis are typically seronegative for RF, although RF is detected in 5-9% of patients. RF testing is usually associated with a high false-positive rate; thus, RF-positive and RF-negative patients should undergo the same treatment.
    • Antinuclear antibody titers in persons with psoriatic arthritis do not differ from those of age- and sex-matched control populations. In 10-20% of patients with generalized skin disease, the serum uric acid concentration may be increased and, on occasion, may predispose to acute gouty arthritis. Low levels of circulating immune complexes have been detected in 56% of patients with psoriatic arthritis but do not appear to parallel disease activity.
    • The associations of psoriatic arthritis with HLA-B17, -Cw6, -DR4, and -DR7 are described in Genetics. Serum immunoglobulin A levels are increased in two thirds of patients with psoriatic arthritis and in one third of patients with psoriasis.
    • Synovial fluid is inflammatory, with cell counts ranging from 5000-15,000/µL and with more than 50% of cells being polymorphonuclear leukocytes. Within the synovium, the infiltrate consists predominantly of T lymphocytes. Synovial fluid complement levels are either within reference ranges or increased, and glucose levels are within reference ranges.

Imaging Studies

  • Radiological features have helped to distinguish psoriatic arthritis from other causes of polyarthritis. In general, the common subtypes of psoriatic arthritis, such as asymmetric oligoarthritis and symmetric polyarthritis, tend to result in only mild erosive disease. Early bony erosions occur at the cartilaginous edge, and, initially, cartilage is preserved, with maintenance of a normal joint space.
  • Juxta-articular osteopenia, which is a hallmark of rheumatoid arthritis (RA), is minimal in persons with psoriatic arthritis. Asymmetric erosive changes in the small joints of the hands and feet are typical of psoriatic arthritis and have a predilection (in decreasing order) for DIP, proximal interphalangeal, metatarsophalangeal, and metacarpophalangeal joints.
  • Erosive disease frequently occurs in patients with either DIP involvement or progressive deforming arthritis and may lead to subluxation and, less commonly, bony ankylosis of the joint. Erosion of the tuft of the distal phalanx, and even the metacarpals or metatarsals, can progress to complete dissolution of the bone. Although this form of acroosteolysis is not diagnostic, it is highly suggestive of psoriatic arthritis. The pencil-in-cup deformity observed in the hands and feet of patients with severe joint disease usually affects the DIP joints but also may involve the proximal interphalangeal joints.

    Arthritis mutilans (ie, "pencil-in-cup" deformiti...

    Arthritis mutilans (ie, "pencil-in-cup" deformities).

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    Arthritis mutilans (ie, "pencil-in-cup" deformiti...

    Arthritis mutilans (ie, "pencil-in-cup" deformities).

  • CT scanning of the sacroiliac joint may be a sensitive method of visualizing involvement in patients with spondylitis or sacroiliitis.
  • Recent studies have indicated that MRI may be a sensitive method for demonstrating the typical enthesopathic pathology of psoriatic arthritis, particularly in the hands and feet.

Other Tests

  • Traditional methods of monitoring patients with rheumatic conditions include clinical assessment for joint inflammation or damage and radiographic evaluations. The radiologic scoring methods for evaluating peripheral joints in persons with psoriatic arthritis were developed for patients with RA. A study validated the original Steinbrocker method, a modified Steinbrocker method, and the Larsen method for assessment of radiographs in patients with psoriatic arthritis. The latter 2 methods can now be used to assess disease progression in patients with psoriatic arthritis.

Histologic Findings

The histopathology of psoriatic synovitis is similar to that observed in other inflammatory arthritides, with a notable lack of intrasynovial immunoglobulin and RF production and a greater propensity for fibrous ankylosis, osseous resorption, and heterotopic bone formation.

More on Psoriatic Arthritis

Overview: Psoriatic Arthritis
Differential Diagnoses & Workup: Psoriatic Arthritis
Treatment & Medication: Psoriatic Arthritis
Follow-up: Psoriatic Arthritis
Multimedia: Psoriatic Arthritis
References
Further Reading
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Further Reading

For additional information, see Medscape’s Psoriasis Resource Center and Arthritis Resource Center.

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Keywords

psoriatic arthritis, spondylitic psoriatic arthritis, rheumatoid psoriatic arthritis, psoriasis, arthritis, skin disease, bone disease, rheumatism, rheumatoid arthritis, psoriatic arthropathy, arthritis mutilans, arthropathia psoriatica, psoriatic spondylitis, asymmetrical seronegative oligoarticular arthritis, dactylitis, sausage digits, pencil-in-cup radiograph, opera-glass hand, asymmetrical oligoarticular arthritis, symmetrical polyarthritis, distal interphalangeal arthropathy, juvenile psoriatic arthritis, sacroiliitis

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Contributor Information and Disclosures

Author

Anwar Al Hammadi, MD, FRCPC, Consultant Dermatologist, Assistant Clinical Professor of Dermatology, University of Sharjah, Dubai, United Arab Emirates
Anwar Al Hammadi, MD, FRCPC is a member of the following medical societies: American Academy of Dermatology, Canadian Dermatology Association, Royal College of Physicians and Surgeons of Canada, and Skin Cancer Foundation
Disclosure: Nothing to disclose.

Medical Editor

Kristine M Lohr, MD, MS, Program Director, Professor, Department of Internal Medicine, Division of Rheumatology and Women's Health, University of Kentucky School of Medicine
Kristine M Lohr, MD, MS is a member of the following medical societies: American College of Physicians, American College of Rheumatology, and American Medical Women's Association
Disclosure: Nothing to disclose.

Pharmacy Editor

Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine
Disclosure: Nothing to disclose.

Managing Editor

Elliot Goldberg, MD, Dean of the Western Pennsylvania Clinical Campus, Professor, Department of Medicine, Temple University School of Medicine
Elliot Goldberg, MD is a member of the following medical societies: Alpha Omega Alpha, American College of Physicians, and American College of Rheumatology
Disclosure: Nothing to disclose.

CME Editor

Alex J Mechaber, MD, FACP, Associate Dean for Undergraduate Medical Education, Associate Professor of Medicine, University of Miami Miller School of Medicine
Alex J Mechaber, MD, FACP is a member of the following medical societies: Alpha Omega Alpha, American College of Physicians-American Society of Internal Medicine, and Society of General Internal Medicine
Disclosure: Nothing to disclose.

Chief Editor

Herbert S Diamond, MD, Professor of Medicine, Temple University School of Medicine; Chairman Emeritus, Department of Internal Medicine, Western Pennsylvania Hospital
Herbert S Diamond, MD is a member of the following medical societies: Alpha Omega Alpha, American College of Physicians, American College of Rheumatology, American Medical Association, and Phi Beta Kappa
Disclosure: medifocus Honoraria Review panel membership; health dialogs Honoraria Consulting; West Penn Allegheny Health System None Board membership

 
 
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