Background Polymyalgia rheumatica (PMR) and giant cell arteritis (GCA) are inflammatory conditions of unknown etiology. They are by some authors considered as manifestations of the same disease and are both treated with corticosteroids. However, a specific diagnosis is important because of different steroid requirements, as well as the risk of vascular complications associated with GCA. Temporal artery biopsy is the gold standard for the diagnosis of GCA, although the presence of skip lesions may render the test negative. PMR is a clinical diagnosis. FDG PET-CT is a non-invasive diagnostic tool that, by using radioactive labeled fluoro-18-deoxyglucose (FDG), visualizes increased metabolic activity in both malign and inflammatory tissue including large vessel inflammation.

Objectives To evaluate the contribution of PET-CT in the diagnosis of PMR and GCA.

Methods Patients registered in our department in 2011-2012, who were diagnosed with PMR or GCA and at the time of diagnosis underwent PET-CT scan as well as biopsy of the temporal artery within a time span of one month were included. Biopsy was performed prior to or within a week after initiation of steroid therapy. We used kappa statistics.

Results 22 patients were included (8 males,14 females). 8 had a clinical diagnosis of PMR, 10 presented with symptoms of GCA and 4 had non-specific symptoms (NSS) including fatigue, fever and high sedimentation rate, where GCA was suspected. Increased FDG-uptake in the large vessels (aorta and its main branches) was found in 10 patients. 5 of them presented with symptoms of GCA, 1 with PMR and 4 with NSS. 4 patients with symptoms of GCA had a positive biopsy, and all showed increased vascular FDG uptake. 2 patients with PMR had a positive biopsy as had 2 patients with NSS. In this agreement and reliability study the kappa coefficient was 0,63, corresponding to a substantial agreement between the biopsy and the PET findings. 1 patient had a positive biopsy and no vascular FDG uptake, whereas 3 patients showed increased vascular uptake and had a negative biopsy. We found inter-observer agreement in 82 % between PET-CT and temporal artery biopsy.

Conclusions FDG PET-CT definitely has a role in the diagnosis of GCA and should be considered in patients with negative temporal artery biopsy, for the diagnosis of GCA and to rule out differential diagnosis that may mimic PMR such as malignancy. Our findings support the theory that PMR and GCA are different manifestations of the same disease.

References

1. Tanaz A Kermani et al. Polymyalgia rheumatica, Lancet 2013;381:63-72

2. D. Blockmans et al. New arguments for a vasculitic nature of polymyalgia rheumatica using positron emission tomography. Rheumatology 1999;38:444-447

Disclosure of Interest None Declared