E003 Why do rheumatologists request PET-CT scans and what do they show: an audit from a tertiary London Hospital

Abstract

Abstract Background/Aims (18F)FDG PET-CT is an imaging tool with utility in the diagnosis of inflammation, infection and malignancy. In rheumatology settings, it is most commonly used for the diagnosis and monitoring of large vessel vasculitis (LVV), sarcoidosis, polymyalgia rheumatica (PMR), IgG-4 disease and myositis. Whilst PET-CT is highly sensitive for the detection of inflammation, concurrent corticosteroid use impairs this. Furthermore, uptake can be non-specific and incidental abnormalities are often reported. Few cohorts have investigated the real-life use of PET-CT including clinical indication, rheumatological and non-rheumatological findings and patient outcomes. Methods 98 PET-CT scans were requested by the rheumatology department at St Georges NHS Foundation Trust from January 2017 to December 2021. Data including patient demographics, pre-existing rheumatological disease, corticosteroid use and inflammatory marker levels were collected. Indication for PET-CT and PET-CT findings were reviewed. Results As summarised in Table 1, PET-CT scans were most commonly requested for the investigation of raised inflammatory markers, poor response to therapy, concerning clinical features, for the characterisation of abnormal imaging findings and for routine monitoring of disease. LVV and malignancy were the most commonly considered differential diagnoses. At the time of PET-CT scan, 59 (60%) patients were taking corticosteroids. 58 of these patients were prescribed prednisolone (dose ranging between 2mg to 80mg, mean dose 19.6mg OD, median dose 15mg OD) In our audit, 39.8% of PET-CT showed active rheumatological disease. 32.6% showed non-rheumatological abnormalities with 2% demonstrating new cancer diagnoses. The detection of incidental non-specific imaging findings commonly led to the request of further diagnostic tests including ultrasound imaging (11 patients) and endoscopy (7 patients). Conclusion In conclusion, PET-CT is a useful imaging tool in the diagnosis and monitoring of rheumatological inflammatory conditions. Despite a majority of patients taking corticosteroids at the time of scan, PET-CT remained an effective diagnostic adjunct. A large number of non-rheumatological imaging abnormalities were seen in our cohort; in most cases, the clinical significance was not immediately clear and further investigations were needed. Further guidance is needed to determine the characterisation and management of these incidental findings to avoid unnecessary, costly and sometimes invasive tests. Disclosure K. Biddle: None. K. Chaabo: None.