An Imposter Twice Over: A Case of IgG4-Related Disease

IgG4-RD has the ability to mimic other pathologic conditions, requiring that health care professionals have a high index of suspicion to make a proper diagnosis.

Citrulline dependence of anti-cyclic citrullinated peptide antibodies in systemic lupus erythematosus as a marker of deforming/erosive arthritis

OBJECTIVE

Anti-cyclic citrullinated peptide (CCP) antibodies are a serological marker for rheumatoid arthritis (RA); up to 10%-15% of patients with systemic lupus erythematosus (SLE) are also positive. While anti-CCP in RA is citrulline-dependent, anti-CCP in some other diseases is citrulline-independent and reacts with both CCP and the unmodified (arginine-containing) cyclic arginine peptide (CAP). We investigated the citrulline dependence of anti-CCP and its significance in the arthritis of SLE.

METHODS

IgG anti-CCP was compared by ELISA to anti-CAP in sera from patients with SLE (n = 335) and RA (n = 47) and healthy controls (n = 35). SLE patients were divided into 5 groups based on their joint involvement: subset I: deforming/erosive arthritis (n = 20); II: arthritis fulfilling (or likely fulfilling) American College of Rheumatology criteria for RA but without erosions (n = 18); III: joint swelling but not fulfilling RA criteria (n = 39); IV: arthritis without documented joint swelling (n = 194); and V: no arthritis (n = 58).

RESULTS

Anti-CCP (> 1.7 units) was found in 68% (32/47) of patients with RA and 17% (55/329) of those with SLE. It was more common in SLE patients with deforming/erosive arthritis (38%). High anti-CCP (> 10 units) was found in RA (26%) and deforming/erosive SLE (12%). High anti-CCP/CAP ratios (> 2, indicating a selectivity to CCP) were found in 91% of anti-CCP-positive RA and 50% of anti-CCP-positive SLE patients with deforming/erosive arthritis. Patients from subset II did not have high anti-CCP/CAP.

CONCLUSION

Citrulline dependence or high levels (> 10) of anti-CCP were common in SLE patients with deforming/erosive arthritis, while most anti-CCP in SLE patients was citrulline-independent. This may be useful in identifying a subset of SLE patients with high risk for development of deforming/erosive arthritis.

Autoantibodies to RNA helicase A: A new serologic marker of early lupus

OBJECTIVE

To investigate the clinical and immunologic significance of autoantibodies to RNA helicase A (RHA) in patients with systemic rheumatic diseases.

METHODS

The study group comprised 1,119 individuals enrolled in the University of Florida Center for Autoimmune Diseases registry from 2000 to 2005. Diagnoses were based on standard criteria. Autoantibodies were analyzed by immunoprecipitation and Western blot assays.

RESULTS

Anti-RHA was observed in 17 (6.2%) of 276 patients with systemic lupus erythematosus (SLE), 2 patients with antiphospholipid antibodies, and 3 other patients, but anti-RHA was not observed in any patient with polymyositis/dermatomyositis, systemic sclerosis, rheumatoid arthritis, or Sjögren's syndrome. Anti-RHA was present in only 2.9% of African American patients, compared with 6.0% of white patients and 12-25% of patients of other races; this was in striking contrast to the frequency of anti-Sm in African American patients (27.2%). Among patients with SLE, anti-RHA was common in young patients (26% of those whose initial visit was at an age younger than 20 years versus 3-4% of those who were initially seen at ages 20-49 years) and at an early stage of disease (23% of those whose first clinic visit was within 1 year of disease onset versus 2-8% of those whose first visit was at least 1 year after disease onset). In 9 of 11 patients, levels of anti-RHA decreased to <10% of the initial value within 9-37 months, while levels of coexisting anti-Ro or anti-Su remained the same. New specificities developed in 2 patients (anti-nuclear RNP and anti-Sm, and anti-ribosomal P, respectively). These data suggest that the level of anti-RHA diminishes over time, and that anti-RHA is regulated via a mechanism different from that for other lupus-related autoantibodies.

CONCLUSION

Anti-RHA is a new serologic marker for SLE. It is produced mainly in young non-African Americans at an early stage of their disease. Anti-RHA has a unique tendency to diminish over time. The production of anti-RHA may depend on a process restricted to early SLE, or it may be highly sensitive to treatment.