Fluorescent in situ hybridization can be used as a complementary assay for the diagnosis of Tropheryma whipplei infection

Background Immunohistochemistry and Periodic acid–Schiff (PAS) staining have been routinely used for the diagnosis of Whipple’s disease (WD). However, these methods present limitations. As a result, the last years, Fluorescence in situ hybridization (FISH) has been increasingly used as a complementary tool for the diagnosis of WD from various tissue samples. Case report In this study, we visualized, by FISH, Tropheryma whipplei within macrophages of a lymph node from a patient with WD. Moreover, we report in this study a patient with a pulmonary biopsy compatible with WD by PAS, immunostaining and FISH, although the specific molecular assays for T. whipplei were negative. Sequencing analysis of the 16S rDNA revealed a T. whipplei -related species with unknown classification. Conclusion FISH can be a valuable method for the detection of Tropheryma species in formalin-fixed paraffin-embedded tissues. FISH cannot replace the other already approved diagnostic techniques for WD, it can be used as a complementary tool and can provide supplementary information in a relatively short time.