How Is RA or SLE Differentially Diagnosed?
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
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. In years past, when they were done by radio-immunoprecipitation (the Farr assay) or by the Crithidia luciliae immunofluorescent test, 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). 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.
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 the Expert
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. In years past, when they were done by radio-immunoprecipitation (the Farr assay) or by the Crithidia luciliae immunofluorescent test, 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). 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.
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