Use of patient age and anti-Ro/La antibody status to determine the probability of patients with systemic lupus erythematosus and sicca symptoms fulfilling criteria for secondary Sjögren's syndrome

A. Prabu1, T. Marshall2, C. Gordon3, T. Plant4, A. Bawendi3, S. Heaton3, S. Jobson5, D Briggs5 and S. J. Bowman1,3,

1 Birmingham Heartlands and Solihull Hospitals NHS Trust,
2 Department of Public Health and Epidemiology,
3 Department of Rheumatology and
4 Department of Immunology, University of Birmingham and
5 Histocompatibility and Immunogenetics Laboratory, National Blood Service, Birmingham, UK

SIR, The development of internationally agreed diagnostic/classification criteria for the diagnosis of both primary and secondary Sjögren's syndrome (SS) has been a major advance for clinical research into this condition [1, 2], enabling clinical therapeutic trials and other studies to generate widely generalizable and accepted results.

The presence of antibodies directed against Ro and/or La antigens (Ro/La) is required in order to fulfil these criteria in patients with primary SS who have not had a labial gland biopsy performed or in whom this did not yield a diagnostic result [2]. The criteria for secondary SS include subjective dry eye and/or dry mouth symptoms and two of the following: objective evidence of reduced tear formation; objective evidence of reduced salivary flow rate; and a positive labial gland biopsy [1]. Anti-Ro/La antibodies have not, however, been included in the criteria for secondary SS as they have not shown significant results using univariate analysis [1]. It is well established that the prevalence of SS among rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE) patients increases with patient age [3], but this also does not form part of the classification criteria.

In our experience, patients with secondary SS in conjunction with RA or SLE rarely undergo labial gland biopsy to confirm the diagnosis. This creates a real problem for research studies by generating a category of patients with ‘probable’ SS who have objective evidence of either dry eyes or mouth but not both, and therefore cannot be fully categorized as having or not having ‘definite’ secondary SS [1]. In order to address this problem we set out to see whether a statistical approach could be used to classify at least some of these patients with reasonable certainty.

In the absence of a clear a priori basis for a power calculation, we decided that 100 consecutive female Caucasian patients fulfilling the 1982 revised criteria for the classification of SLE [4] was a reasonable number for initial hypothesis-testing and were able to recruit 96 such patients. None had had a labial gland biopsy. For comparison, we also studied 100 female Caucasian patients with RA attending rheumatology clinics in Birmingham, UK. After we had obtained written informed consent, all patients answered the six ‘sicca’ questions of the EU classification criteria, underwent a Schirmer-I test and measurement of unstimulated salivary flow rate, and had their serum immunoglobulin (Ig) levels and anti-Ro/La antibody titres measured, the latter by an ELISA (enzyme-linked immunosorbent assay; Binding Site, Birmingham, UK) validated with international standardized sera. HLA-DR and DQ typing was performed on peripheral venous blood stored in EDTA (ethylenediamine tetraacetate) using a polymerase chain reaction-based technique [5]. These variables were analysed using binary logistic regression analysis and, where indicated, two-by-two tables. This study formed part of a larger study for which West Midlands Multicentre Research Ethics Committee approval had been received.

Of the 96 SLE patients, 18 (19%) and 10 (10%) could be diagnosed as having ‘definite’ and ‘probable’ secondary SS respectively in the absence of labial gland biopsy data. As well as studying the potential contributions of age and anti-Ro/La antibody status, we also examined the contribution of disease duration, IgG and/or IgA levels and HLA-DR and DQ type in classifying SLE patients correctly into those with and without secondary SS.

In order to increase the power of the statistical analysis, we followed standard statistical procedure by including only patients with ‘definite’ secondary SS and those without secondary SS in the analysis. The mean age of these 86 patients was 47.6 yr (range 30–80) and the mean disease duration was 10.9 yr (range 1–60). Anti-Ro/La antibodies were positive in 42 patients (49%). Using a convenient cut-off of age 50 yr in these initial analyses to divide the patients into two groups of approximately similar numbers, the odds ratio for the presence of secondary SS in patients over 50 yr of age, compared with those below this age, was 11.96 [95% confidence interval (CI) 2.89–49.60] and for the presence of anti-Ro/La antibodies compared with those without anti-Ro/La antibodies it was 3.95 (95% CI 1.10–14.14). Combining these two parameters, the likelihood ratio associated with a greater than 50% probability of having secondary SS in anti-Ro/La antibody-positive patients over age 50 yr was 5.19, with a specificity and sensitivity of 88% and 61% respectively.

Disease duration of more than 10 yr and raised IgG or IgA levels, with odds ratios of 1.18 and 0.85 respectively, were not helpful in the diagnosis of secondary SS.

HLA-DR and DQ genotyping data were available for 83 of these 86 patients. Ten of 17 patients (59%) with definite secondary SS and 27 of 66 patients (41%) without secondary SS were HLA-DR3-positive (odds ratio=1.79, 95% CI 0.49–6.61). As this only contributes a maximum of 4% to the event probability calculation and, unlike anti-Ro/La antibody testing, is not routinely clinically available, it is unlikely to be of substantial value and we do not pursue its use in the analyses set out below.

In order to assign an individual probability value for the presence of ‘definite’ secondary SS according to the patient's age and anti-Ro/La antibody status, the probability of ‘definite’ secondary SS was plotted against patient age expressed as a continuous variable, for both the anti-Ro/La antibody-positive and -negative groups, using logistic regression analysis (Fig. 1Go).



View larger version (9K):
[in this window]
[in a new window]
 
FIG. 1. Graphical representation of the probability values for the fulfilment of diagnostic/classification criteria for secondary SS in female Caucasian patients with SLE according to their age and anti-Ro/La antibody status. {blacksquare}, Ro/La+; {blacktriangleup} Ro/La-.

 
If we apply the conclusions of this analysis to the 10 patients with ‘probable’ secondary SS, this generates the following data: three patients [two with anti-Ro/La antibodies (age 58 and 52 yr) and one without (age 70 yr)] had probabilities of 33–45% for the presence of ‘definite’ secondary SS, which still makes them difficult to classify with certainty. The remaining seven patients (only one of whom was anti-Ro/La antibody positive; age range 32–65 yr) had probabilities of less than 25% of having secondary SS, making it unlikely that they would fulfil the EU criteria even were a labial gland biopsy to be performed.

By contrast, only three out of the 100 RA patients (3%) were positive for anti Ro/La antibodies, of whom one had ‘probable’ secondary SS (33%) and the other two did not have secondary SS. Of the remaining 97 patients without anti-Ro/La antibodies, 22 (23%) had ‘probable’ and four (4%) had ‘definite’ secondary SS. The low frequency of anti-Ro/La antibodies among RA patients is similar to that reported previously [6] and confirms that these antibodies are unlikely to be contributory in this group of patients. HLA-DR and DQ typing data were available on 94 RA patients. There were no significant HLA-DR or DQ frequency differences between the groups of RA patients with and without probable or definite secondary SS (HLA-DR4, 71–78%; DR3, 22–24%; DR2, 17–19%). As only four RA patients had definite secondary SS, we were unable to evaluate this group separately. We could not, therefore, develop this approach to classify RA patients with ‘probable’ SS.

The results of this analysis support our a priori expectation of an association between the presence of anti-Ro/La antibodies and the development of secondary SS in female Caucasian patients with SLE, which differs from the conclusions of some other studies [3]. In terms of our proposal, inspecting the probability curve (Fig. 1Go) shows that anti-Ro/La antibody-positive patients over 60 yr old have a probability of ‘definite’ secondary SS of over 50% while this probability falls to less than 25% in anti-Ro/La antibody-negative patients below this age.

This approach is of greatest value in identifying patients with a low probability of having ‘definite’ secondary SS rather than identifying those with a high probability. The analysis has enabled us to reclassify seven of the 10 ‘probable’ secondary SS into ‘without’ secondary SS and left only three patients still requiring a labial gland biopsy in order to be definitively assigned.

Clearly, our underlying assumption requires formal testing in a cohort of patients who have undergone labial gland biopsy, and consensus needs to be reached over the probability cut-off values that are sufficient to assign patients to the groups. While the formal international diagnostic/classification criteria are now established [2], our approach is simple to apply and could be of benefit in research studies as well as in advising patients in the routine clinical setting.

Notes

Correspondence to: S. J. Bowman, Department of Rheumatology, The Medical School, The University of Birmingham, Edgbaston, Birmingham B15 2TT, UK. E-mail: s.j.bowman{at}bham.ac.uk Back

References

  1. Vitali C, Bombardieri S, Moutsopoulos HM et al. Preliminary criteria for the classification of Sjögren's syndrome. Results of a prospective concerted action supported by the European Community. Arthritis Rheum 1993;36:340–7.[ISI][Medline]
  2. Vitali C, Bombardieri S and the European Study Group on diagnostic criteria for SS. European classification criteria for Sjögren's syndrome (SS). Classification criteria for Sjogren's syndrome: a revised version of the European criteria proposed by the American–European Consensus Group. Ann Rheum Dis 2002;61:554–8.[Abstract/Free Full Text]
  3. Nossent JC, Swaak AJG. Systemic lupus erythematosus VII: frequency and impact of secondary Sjögren's syndrome. Lupus 1998;7:231–4.[ISI][Medline]
  4. Tan EM, Cohen AS, Fries JF et al. The 1982 revised criteria for the classification of systemic lupus erythematosus. Arthritis Rheum 1982;25:1271–7.[ISI][Medline]
  5. Bunce M, O'Neill CM, Barnardo MC et al. Phototyping: comprehensive DNA typing for HLA-A, B, C, DRB1, DRB3, DRB4, DRB5 and DQB1 by PCR with 144 primer mixes utilizing sequence-specific primers (PCR-SSP). Tissue Antigens 1995;46:355–67.[ISI][Medline]
  6. Boire G, Menard HA, Gendron M, Lussier A, Myhal D. Rheumatoid arthritis: anti-Ro antibodies define a non-HLA-DR4 associated clinicoserological cluster. J Rheumatol 1993;20:1654–60.[ISI][Medline]
Accepted 11 June 2002





This Article
Full Text (PDF)
Alert me when this article is cited
Alert me if a correction is posted
Services
Email this article to a friend
Similar articles in this journal
Similar articles in ISI Web of Science
Similar articles in PubMed
Alert me to new issues of the journal
Add to My Personal Archive
Download to citation manager
Disclaimer
Request Permissions
Google Scholar
Articles by Prabu, A.
Articles by Bowman, S. J.
PubMed
PubMed Citation
Articles by Prabu, A.
Articles by Bowman, S. J.
Related Collections
Other Rheumatology