Introduction: Positron emission tomography (PET) is a non-invasive diagnostic method which shows the bio-distribution of positron emitter labelled radiopharmaceuticals in the body. Due to the fact that not only timorous, but in certain conditions also some inflammatory cells may exhibit increased accumulation of 18F-FDG, 18F-FDG PET can be used in the diagnosis of both tumours and certain types of inflammations.
Objective: The objective of the study is to asses the benefits of 18F-FDG PET in the patients examined for symptoms of fever of uncertain origin whose results suggested the possibility of large vessel vasculitis.
Sample and methods: In the years 2003 and 2004, the positron emission tomography centre at Masaryk Oncological Institute in Brno examined 35 patients in order to establish the cause of febrilia using 18F-FDG PET. The suspicion of large vessel vasculitis was based on the detection of high accumulation of radiopharmaceuticals in large vessels walls (in the aorta and the larger outgoing branches). The patients underwent a further standard imaging test to diagnose large vessel vasculitis as follows: CT angiography (CTA) in 4 patients, MR angiography (MRA) in 3 patients and duplex ultrasonography (USG) in 7 patients. A definitive diagnosis of primary autoimmunity of large vessel vasculitis was counter checked histologically or based on a therapeutic test by means of the effect of corticotherapy in immunosuppressive doses.
Results: Positive PET findings were recorded in 23 out of 35 patients (65.7%). 11 out of 23 PET positive patients (47.8% of PET positive persons and 31.4% of all patients with febrilia) were suspected to have active large vessel vasculitis based on PET examination. In 10 of the 11 patients, it was possible to perform additional examinations necessary to confirm the diagnosis: a histological test of arteria temporalis in one case, and a therapeutic test using corticotherapy in all 10 cases. Large vessel vasculitis was confirmed in all 10 individuals (2 men and 8 women aged 53-66, median age of 62 years). None of the CTA, MRA or USG examinations in any of the cases detected direct or clear signs ofvasculitis, but 3 CTA and 1 MRA examinations could be considered abnormal. The detection of temporal (giant cell) arteritis based on excision of arteria temporalis superficialis points to the limits of PET examination which is unable to assess veins with a diameter of less than 5 mm. On the other hand, it documents the possibility of extra-cranial damage being proved in this diagnosis with the use PET. In seven of the ten cases, a control PET scan was done during corticotherapy. It showed a drop in the accumulation of radiopharmaceuticals, and therefore a drop in the inflammatory metabolic activity on the walls of the large vessels, which was in line with the drop in the laboratory parameters of the inflammation (FW, CRP).
Conclusion: Positron emission tomography using 18F-FDG can be used to detect active large vessel vasculitis in patients examined for symptoms of fever of uncertain origin. Apparently, PET can detect cases of large vessel vasculitis where other imaging methods have failed and can be also used to follow the development of vasculitis activity during therapy.