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Prevalence of antiphospholipid antibodies in systemic sclerosis and association with primitive pulmonary arterial hypertension and endothelial injury

N. Assous^1*, Y. Allanore^1*, F. Batteux², C. Meune³, P. Toulon⁴, B. Weill², A. Kahan¹

¹Department of Rheumatology A, ²Department of Immunology, ³Department of Cardiology, and ⁴Department of Hematology, Paris 5 University, Assistance Publique Hôpitaux de Paris, Cochin Hospital, Paris, France.

ABSTRACT
Objective
To investigate the prevalence and clinical significance of antiphospholipid antibodies in patients with systemic sclerosis (SSc).

Methods
Autoantibodies against cardiolipin (aCL) and b2-glycoprotein I (b2-GPI) were detected by enzyme-linked immuno-absorbent assays (ELISAs) in successively hospitalised SSc patients admitted during a 24-month period. These patients were compared to patients with systemic lupus erythematosus (SLE), rheumatoid arthritis (RA).

Results
108 SSc patients were included: 61 had limited cutaneous SSc, 47 had the diffuse sub-type, 16 had primitive pulmonary arterial hypertension (PAH) and 34 had digital ulcerations. The control groups consisted of 37 RA and 38 SLE patients. The prevalence of aCL positivity was lower in SSc patients vs SLE patients (14 vs 47%; p < 0.001), lower in RA patients vs SLE patients (19 vs 47%; p < 0.001), and not different in SSc vs RA patients (14 vs 19%; NS). The mean aCL titer was also lower in SSc vs SLE patients (8 ± 10 vs 15 ± 20; p < 0.001). In SSc patients, positivity for aCL was associated with PAH (p = 0.009) and the aCL titer correlated with that of the von Willebrand antigen factor (r = 0.23; p = 0.045).
The prevalence of anti b2-GPI positive patients (IgG and/or IgM) was 5% in the SSc group, 18% in the SLE group and 5% in the RA group (SLE vs SSc and SLE vs RA; p = 0.005).

Conclusion
We found that the prevalence of antiphospholipid antibodies in SSc patients was low. However, aCL antibodies were associated with PAH and endothelial injury.

Key words
Systemic sclerosis, antiphospholipid syndrome, anticardiolipin antibodies, von Willebrand factor, pulmonary arterial hypertension, endothelial injury.

*These authors equally contributed to this study.
Please address correspondence and reprint requests to: Dr Yannick Allanore, Hôpital Cochin, Service de Rhumatologie A, 27 rue du faubourg Saint-Jacques 75014 Paris, France.
E-mail: yannick.allanore@cch.ap-hop-paris.fr