Rheumatology experience with FDG PET / CT in inflammation of unknown origin: a single - centre report for determining factors associated with diagnostic precision.

ABSTRACT

BACKGROUND / AIM: The use of PET / CT is becoming more common in the elucidation of inflammatory processes in which the underlying cause cannot be determined by conventional examinations. Although PET / CT is an effective method for detecting inflammatory foci, the precise diagnosis may not be obtained in all cases. In addition, considering factors such as radiation exposure and cost, it becomes important to identify patients who can get results with PET / CT. In this study, it was aimed to examine the factors that can predict the differential diagnostic value of PET / CT by retrospectively scanning patients who underwent PET / CT for inflammation of unknown origin (IUO) in rheumatology practice. METHODS: Demographic, clinical and laboratory information of the patients followed up in our clinic and who underwent PET / CT for differential diagnosis were enrolled. Whether they were diagnosed after PET / CT and during the follow - up period, and their diagnoses were examined. RESULTS: A total of 132 patients were included in the study. A previous diagnosis of rheumatic disease was present in 28.8 % of the patients, and a history of malignancy was present in 2.3 % . The patients were divided into three groups group 1 patients with increased FDG uptake in PET / CT and diagnosis confirmed by PET / CT, group 2 patients with increased FDG uptake in PET / CT but diagnosis was not confirmed, and group 3 patients without increased FDG uptake in PET / CT. Increased FDG uptake in PET / CT was detected in 73 % of the patients. While PET / CT helped the diagnosis in 47 (35.6 %) patients (group 1), it did not help the diagnosis in 85 (64.4 %) (groups 2 and 3). Thirty - one (65.9 %) of the diagnosed patients were diagnosed with a rheumatologic disease. When the 3 groups were compared, male gender, advanced age, CRP levels, presence of constitutional symptoms, SUVmax values and number of different organs with increased FDG uptake were higher in Group 1. Sixty - six percent and 74 % of the patients in groups 2 and 3 were not diagnosed during the follow - up period. No patient in group 3 was diagnosed with malignancy during follow - up. CONCLUSION: PET / CT has high diagnostic value when combined with clinical and laboratory data in the diagnosis of IUO. Our study revealed that various factors can affect the diagnostic value of PET / CT. Similar to the literature, the statistically significant difference in CRP levels shows that patients with high CRP levels are more likely to be diagnosed with an aetiology in PET / CT. Although detection of involvement in PET / CT is not always diagnostic, there was an important finding that no malignancy was detected in the follow - up in any patient without PET / CT involvement. Key points • PET / CT is an effective method for detecting inflammatory foci. • PET / CT has proven to be effective in the diagnosis of rheumatological diseases, the extent of disease and the evaluation of response to treatment. • Indications for the use of PET / CT in the field of rheumatology and the associated factors and clinical features supporting the diagnosis with PET / CT are still to be fully clarified. • In routine practice, with PET / CT, both delays in diagnosis and examinations performed during diagnosis and the cost can be reduced.