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Prevalence and clinical associations of anti-Ku antibodies in patients with systemic sclerosis: a European EUSTAR-initiated multi-centre case–control study

B Rozman¹, S unik¹, S Sodin-Semrl¹, L Czirják², C Varjú², O Distler³, D Huscher⁴, M Aringer⁵, G Steiner⁵, M Matucci-Cerini⁶, S Guiducci⁶, B Stamenkovi⁷, A Stankovi⁷, T Kveder¹

¹ Department of Rheumatology, University Medical Centre, Ljubljana, Slovenia
² Department of Immunology and Rheumatology, Medical School, University of Pécs, Pécs, Hungary
³ Department of Rheumatology, University Hospital Zurich, Zurich, Switzerland
⁴ German Rheumatism Research Centre Berlin, Epidemiology, Berlin, Germany
⁵ Department of Rheumatology, Internal Medicine III, Medical University of Vienna, Vienna, Austria
⁶ Department of Medicine & Surgery, Division of Medicine I & Rheumatology, University of Florence, Florence, Italy
⁷ Department of Rheumatology, Institute for Prevention and Treatment of Rheumatic and Cardiovascular Disease Nika Banja, Medical Faculty, University of Ni, Ni, Serbia

ProfessorDr B Rozman, University Medical Centre, Department of Rheumatology, Vodnikova 62, SI-1000 Ljubljana, Slovenia; kc.lj.rozman{at}siol.net

Objectives: To determine the prevalence of anti-Ku antibodies in 625 patients with systemic sclerosis (SSc) from six European rheumatological centres and to evaluate their clinical and serological characteristics.

Methods: Sera of 625 consecutive patients with either limited cutaneous or diffuse cutaneous SSc were tested for antibodies to Ku antigen together with other extractable nuclear antigens by counterimmunoelectrophoresis. A case–control design with calculation of bootstrap 95% confidence intervals derived from anti-Ku negative control patients was used to evaluate clinical associations of anti-Ku antibodies. Sera from anti-Ku positive patients with SSc and a control group were additionally tested by immunofluorescence on Hep-2 cell substrates and line immunoassay.

Results: Anti-Ku antibodies were found in the sera of 14/625 (2.2%) patients with SSc. Of 14 anti-Ku positive patients with SSc, 10 had no other anti-extractable nuclear antigen (ENA) antibodies detected by counterimmunoelectrophoresis. Using a case–control study design, anti-Ku antibodies were significantly associated with musculoskeletal manifestations such as clinical markers of myositis, arthritis and joint contractures. In addition, a significant negative correlation of anti-Ku antibodies was found with vascular manifestation such as fingertip ulcers and teleangiectasias. There was a striking absence of anti-centromere antibodies as well as anti- polymyositis (PM)/scleroderma (Scl) antibodies in patients that were anti-Ku positive. As expected, anti-Scl70 and punctate nucleolar immunofluorescence patterns were present only in single cases.

Conclusion: This is the largest cohort to date focusing on the prevalence of anti-Ku antibodies in patients with SSc. The case–control approach was able to demonstrate a clinically distinct subset of anti-Ku positive patients with SSc with only relative clinical differences in skeletal features. However, the notable exceptions were signs of myositis. This shows the importance of anti-Ku antibody detection for the prediction of this specific clinical subset.

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