Determination of rickettsial and antinuclear antibodies in Danish patients with sarcoidosis.

Introduction: Rickettsia helvetica has been proposed as an aetiological agent in sarcoidosis.
Objectives: To assess the prevalence of plasma anti-Rickettsia antibodies in a Danish population of patients with sarcoidosis and control subjects. In addition, we evaluated the presence of plasma antinuclear antibodies (ANAs).
Methods: Plasma samples from 49 consecutive patients (27 male, 22 female, median age 38 years, interquartile range 32-51 years) were compared with plasma from 51 age- and sex-matched controls (28 male, 23 female, median age 40 years, interquartile range 33-49 years), using a commercially available immunofluorescence assay testing for antibodies towards spotted fever group and typhus group Rickettsia as well as an assay for ANA. We obtained information regarding tick exposure and sarcoid disease manifestations from the medical records.
Results: The prevalence of antibodies to Rickettsia in patients with sarcoidosis 1/49 (2%) was not significantly different from the prevalence in the controls 4/51 (8%). The prevalence of ANA was 2/49 (4%) in the patients and 3/51 (6%) in the controls.
Conclusions: The results do not support the hypothesis that Rickettsia or ANAs should be involved in the pathogenesis of sarcoidosis. Seventy-one per cent of the patients were under treatment with prednisolone in the 3 months leading up to the blood sample. We assume that antibody-related serological methods for various reasons could be inadequate to diagnose a chronic rickettsial infection.