Granuloma annulare displaying pseudorosettes in Borelia infection.

AIMS In 2003, pseudorosettes were described as highly suspicious of infection by Borrelia burgdorferi sensu lato in the appropriate clinical context. Nevertheless, such a pattern has been described in the literature in other non-infectious conditions. On the other hand, granuloma annulare (GA) has been recently closely associated with infection by Borrelia. We investigated how frequently pseudorosettes can be detected in common GA cases confirmed for Borrelia by PCR. METHODS AND RESULTS We studied 13 biopsies of non-interstitial GA and 2 biopsies of interstitial GA from patients without clinical suspicion of borrelial infection. We also performed immunohistochemical studies in all the biopsies, using the CD-68 antibody. Molecular studies with PCR were performed with beta-globin PCR (human DNA). Borrelial DNA was confirmed by amplifying the OspA gene and intergenic rrf-rrl region. We found histiocytic pseudorosettes in 13 biopsies (86.66%). Human DNA was successfully amplified from 8 of 13 paraffin-embedded skin samples. From these we amplified borrelial DNA in 5 of 8 samples. Out of the 8 cases in which human DNA was amplified, a correlation between pseudorosettes and the molecular tests (Borrelia DNA) was confirmed in 5 instances. CONCLUSIONS a) Pseudorosettes are not an unusual finding in common granuloma annulare; b) Borrelia is present in (most) cases of granuloma annulare; and c) Pseudorosettes seem to be a good morphological sign predictive of infection with Borrelia in granuloma annulare.