How Is RA or SLE Differentially Diagnosed?

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How Is RA or SLE Differentially Diagnosed in a Patient With

Polyarthritis?



Question

A 26-year-old female patient presented to her physician complaining

of polyarthritis. The presentation and distribution of her complaint

are suggestive of rheumatoid arthritis (RA). Laboratory exam revealed

erythrocyte sedimentation rate 130, white blood cell count 9000,

positive rheumatoid factor (RF), positive anti-double strand

antinuclear antibody (ANA), and possible antinuclear factor. The

patient was prescribed 5 mg prednisolone per day. Given the patient's

presentation and laboratory results, which would be the correct

diagnosis: RA or systemic lupus erythematosus (SLE)?

Jasim Obaid, MD



Response from Arthur Kavanaugh, MD

University of California at San Diego, Division of Rheumatology,

Allergy, and Immunology, La Jolla, California.



Laboratory testing has a long and storied history in rheumatology. In

the middle of the last century, tests such as the ANA and RF helped

physicians establish diagnoses for several rheumatic conditions.

Further refinements and newer tests generated even greater utility.

Testing for antibodies to double-stranded DNA (anti-dsDNA) had

previously been among the most useful in rheumatology.[1] In years

past, when they were done by radio-immunoprecipitation (the Farr

assay)[2,3] or by the Crithidia luciliae immunofluorescent test,[4]

these tests were highly specific for the diagnosis of SLE. However,

more recently, these tests have been supplanted by other methods,

particularly the enzyme-linked immunosorbent assay (ELISA).[5] While

high titers of anti-dsDNA by ELISA perform comparably to the older

tests, there is much less specificity at lower titers. Also, no

rheumatologic test is perfect. Even with a highly specific test such

as the anti-dsDNA, there are still patients with other diseases, such

as RA, who may be found to have a positive test result. In this case,

with the information presented, the diagnosis could be either RA or

SLE. If there are no other features suggestive of SLE, and if there

are other features suggestive of RA (eg, rheumatoid nodules,

periarticular erosions), RA may be the best diagnosis. Because it is

more specific than RF, the presence of anti-CCP [anticyclic

citrullinated peptide] antibodies might also help suggest that RA is

the diagnosis.[6]



Posted 03/09/2006



References

Kavanaugh A, D; American College of Rheumatology Ad Hoc

Committee on Immunologic Testing Guidelines. Guidelines for

immunologic laboratory testing in the rheumatic diseases: anti-DNA

antibody tests. Arthritis Rheum. 2002;47:546-555. Abstract

Farr RS. A quantitative immunochemical measure of the primary

interaction between IxBSA and antibody. J Infect Dis.

1958;103:239-262. Abstract

Strickland PT, Boyle JM. Application of the Farr assay to the

analysis of antibodies specific for UV irradiated DNA. J Immunol

Methods. 1981;41:115-124. Abstract

Mauff AC. The Crithidia luciliae immunofluorescent test for the

detection of antibodies to native DNA. S Afr Med J. 1981;59:69-70.

Abstract

Wallace DJ, Salonen EM, Avaniss-Aghajani E, et al. Anti-telomere

antibodies in systemic lupus erythematosus: a new ELISA test for anti-

DNA with potential pathogenetic implications. Lupus. 2000;9:328-332.

Abstract

Riedemann JP, Munoz S, Kavanaugh A. The use of second generation anti-

CCP antibody (anti-CCP2) testing in rheumatoid arthritis. A

systematic review. Clin Exp Rheumatol. 2005;23(Suppl 39):S69-S76.

http://www.medscape.com/viewarticle/523792