Is sarcoidosis a rickettsiosis? An archival study.

Background: Based on earlier research, Rickettsia helvetica could possibly be involved in the pathogenesis of sarcoidosis. Rickettsiae are transmitted to humans by a tick vector, Ixodes ricinus; this tick is highly prevalent in Northern Europe. We aimed to investigate the association between evidence of rickettsiae and sarcoidosis in histological samples. Methods: We included formalin-fixed, paraffin-embedded mediastinal lymph node biopsies from 52 ethnic Danish patients with sarcoidosis and compared these with 50 biopsies from ethnic Danish patients with mediastinal lymphadenopathy of other causes. Samples were analysed for: (1) rickettsial DNA by real-time polymerase chain reaction (PCR) and (2) rickettsial rDNA (ribosomal DNA) by a specific fluorescence in situ hybridization technique (FISH). Results: Rickettsia was not detected in biopsies by real-time PCR and/or FISH analyses. Conclusion: Our results do not support the hypothesis that Rickettsia is involved in the pathogenesis of sarcoidosis.