Assesment of different bioptic and immunohistochemical techniques for the diagnosis of feline infectious peritonitis (FIP)

ASSESMENT OF DIFFERENT BIOPTIC AND IMMUNOHISTOCHEMICAL TECHNIQUES FOR THE DIAGNOSIS OF FELINE INFECTIOUS PERITONITIS (FIP) Saverio Paltrinieri, Alessia Giordano, Emanuela Milesi, Gabriele Ghisleni, Margherita Parodi Cammarata Dipartimento di Patologia Animale, Igiene e Sanità Pubblica Veterinaria, Via Celoria 10, Milano, Italy Aim of the study - Haematological and electrophoretical changes might be highly suggestive of Feline Infectious Peritonitis (FIP), but the in vivo diagnosis of FIP can be hazardous. Gross and histological findings are often diagnostic and the feline coronavirus (FCoV) can be found within the lesions by immunohistochemistry (IHC), but affected cats are often too compromised to receive anesthesia and laparotomy to be biopsied. For these reasons we tested the diagnostic value of poorly invasive bioptic tecnhniques on effusions, liver and kidney. Material and methods - 10 cats with wet FIP were examined. One ml of effusions, taken in vivo was put in an EDTA coated tube, washed twice with phospate buffered saline (PBS) and cytocentrifuged. At the necropsy core biopsies (CB) using a tru-cut, fine-needle aspirate biopsies (FNAB) and excisional biopsies (EB) were taken. Microthomic sections from formalin-fixed, paraffin-embedded CB and EB were stained with hematoxilin-eosin and IHC, using an anti-FCoV antibody provided by Prof. NC Pedersen (Davis, California) and the avidin-biotin peroxidase complex (ABC) method. Some drops of FNAB samples were smeared, and the remaining amount was put in PBS and cytocentrifuged. Smeared and cytocentrifuged FNAB and effusions were stained with May Grünwald-Giemsa and IHC. Results - Cytology was consistent with FIP in all the effusions and in 6 cases the FCoV was detected by IHC. Fibrinous perihepatitis was detected by gross examination in 5 cats, while perihepatitis and intraparenchimatous foci, were histologically detectable in all the EB, 7 of which were positive by IHC. 7 liver CB had intraparenchimatous foci or perihepatitis, and 2 were positive by IHC. Pyogranulomatous hepatitis was cytologically diagnosed in 6 FNAB, 2 of which were positive by IHC. Gross examination revealed renal nodular lesions in 3 cats. Pyogranulomatous nephritis was present in 4 EB, 2 of which were positive by IHC. 3 renal CB showed lesions consistent with FIP but none was positive by IHC. Cytology consistent with FIP was detected in 4 renal FNAB, one of which was positive by IHC. The characteristics of positivity in all FNAB samples stained by IHC were better in cytocentrifuged than in smeared samples. Conclusions - FIP can be easily diagnosed by cytological and immunohistochemical analysis of the effusions. EB and FNAB can show changes consistent with FIP before the appearance of gross lesions. In contrast the detection of typical lesions in CB and of FCoV by IHC in both CB and FNAB are uncommon, most likely due to the known high variability in the distribution of the lesions in an organ and of the viral antigen among different lesions.