Positron emission tomography in the diagnostic pathway for intracystic infection in adpkd and "cystic" kidneys. a case series

BACKGROUND: Intracystic infection, in Autosomal Dominant Polycystic Kidney Disease (ADPKD) and in kidneys with multiple cysts, is a diagnostic and therapeutic challenge, as conventional imaging techniques may not discriminate among "complicated" cysts (infection, bleeding, neoplasia), and as the clinical picture may be attenuated, in particular in early phases. Positron Emission Tomography with fluorodeoxyglucose (FDG-PET) was recently suggested as a tool to detect infection in ADPKD, in single cases and small series. The aim of the study was to report on the role of FDG-PET in the work-up of 10 cases of suspected cystic infections, affected by ADPKD or with multiple kidney cysts. METHODS: Observational study. Review of clinical charts and of the imaging data since the use of FDG-PET for detecting cystic infections (2008-2010). RESULTS: In 2008-2010, 6 patients with ADPKD and 4 with multiple kidney cysts were referred for suspected intracystic infections (3 males, 7 females, aged 55-83 years, in all CKD stages); in one case the imaging was done in the work-up of a complicated "uremic" cyst. The clinical picture, the usual inflammatory markers and/or the conventional imaging techniques did not allow conclusive diagnosis at referral or during follow-up (ultrasounds in all, CT in 8/10). Nine patients displayed inflammatory signs (increase in C-reactive protein and other biochemical markers) and constitutional symptoms (fever in 9/10). FDG-PET was positive in 6 cases (5 kidney and 1 liver cyst), was repeated during follow-up in 4 patients and was negative in 4 cases. In the positive cases, FDG-PET guided the therapeutic choices; in particular, the duration of therapy was supported by imaging data in the 4 cases with multiple scans. No relapse was recorded after discontinuation of antibiotic therapy in the treated patients. The negative cases did not develop clinical signs of cystic infection over follow-up. CONCLUSION: In this case series, the largest prospective one so far published and the only one including different types of renal cysts, FDG-PET is confirmed as a promising diagnostic tool for detecting intracystic infection in ADPKD and in multiple kidney cysts, and a potential guide for tailoring therapy. Further larger and multicenter studies are needed to evaluate the cost-benefit ratio and the limits of this imaging technique in the clinical setting.