Background/Purpose:

Fluoro-deoxy-glucose positron emission tomography with computerised tomography (PET/CT) is an imaging modality which identifies tissues with high metabolic activity. It is used in the diagnosis of patients with malignancy, infections, inflammatory diseases and pyrexia of unknown origin (PUO). Although useful, PET/CT has a high radiation dose of 14mSv and therefore should be used cautiously. We investigated the role of PET/CT in general rheumatology practice aiming to understand the indications, diagnostic yield and whether there was additional benefit to whole-body CT (WB-CT).

Methods:

PET/CT requests arranged by 8 rheumatologists between January 2008 and April 2015 were retrospectively reviewed for indication, inflammatory markers, PET/CT, WB-CT findings and final diagnoses. Definitions for analysis: true positive – PET/CT abnormality directly contributing to diagnosis, false positive – abnormality not contributing to diagnosis, true negative- normal scan, false negative- normal scan but disease process identified at 6 months follow-up. A final diagnosis was made by physician assessment, other investigations and tissue biopsy where indicated.

Results:

80 PET/CT requests were identified (55 females), mean age 63 years (range 24-86). A final diagnosis was established in 86%. Indications included large vessel vasculitis (34), disease activity progression (3), infection (2), malignancy (22), PUO (2), unexplained inflammatory response (18).

Two sub-groups were analysed; first presentation with no diagnosis (n=53) and prior established rheumatological diagnosis (n=27).

First presentation: PET/CT identified abnormalities in 23/53 (43%) cases, of which 10 (43%) contributed to diagnosis (malignancy-2, large vessel vasculitis-6, PMR-1 and infection-1). 13 (25%) identified non-specific abnormalities with no contribution to a final diagnosis. 16 (30%) were negative and no new diagnosis was apparent at 6 months follow-up. Ten patients did not reach a final diagnosis. The sensitivity in this setting was 45% and specificity 76%.

Established rheumatological diagnoses included myositis, rheumatoid arthritis, scleroderma, Takayasu’s, GCA, JIA, lupus, PMR, undifferentiated and mixed connective tissue disease. PET/CT was positive in 15/27 cases (56%), identifying new diagnoses in 10 patients (5 aortitis, 1 Takayasu’s, 1 Polymyositis, 2 infection, 1 vasculitic myositis) and increase in disease activity in 2 (inflammatory arthritis in scleroderma and JIA). Non-specific abnormalities were apparent in 3 cases. 12 had truly normal scans.

PET/CT added no further information to WB-CT in 31/45 (69%) patients including those diagnosed with malignancy. However PET/CT directly diagnosed Takayasu’s arteritis in 1, aortitis in 3 cases and inflammatory arthritis in 2, which was not apparent on WB-CT. The mean ESR was 76 in patients with a truly positive scan versus 44 with a truly negative PET/CT.

Conclusion:

PET/CT has moderate diagnostic sensitivity and reasonable specificity in general rheumatology practice and often appears to provide no further information to WB-CT. Its main diagnostic advantage is for aortitis, and an elevated ESR may improve its diagnostic yield.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/to-pet-or-not-to-pet-in-general-rheumatology-practice/