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Defining the clinical utility of PET or PET-CT in idiopathic inflammatory myopathies: A systematic literature review.

OBJECTIVES
Positron emission tomography (PET), often combined with computed tomography (CT), is a well-established tool for diagnosing malignancy and inflammatory disease. The idiopathic inflammatory myopathies (IIM) are chronic, multi-system diseases characterised by skeletal muscle inflammation, the potential for extramuscular manifestations such as interstitial lung disease (ILD) and an increased risk of malignancy. We performed a systematic literature review to evaluate the utility of PET or PET-CT in evaluation of IIM.


METHODS
A search of Medline and EMBASE from 1990 to 2022 using keywords related to IIM and PET was performed. English language studies of adults with IIM who had PET or PET-CT were included.


RESULTS
Our search identified 1173 potentially relevant abstracts, 19 of which were included. The majority of studies used [18F] fluorodeoxyglucose (FDG) PET or PET-CT scans, while the remainder used [18F] florbetapir and [11C] Pittsburgh compound B ([11C] PIB). The sensitivity and specificity of 18F-FDG-PET or 18F-FDG-PET-CT for diagnosing malignancy compared with standard detection methods was 66.7-94% and 80-97.8%, respectively. The sensitivity of 18F-FDG PET-CT for ILD was 93-100% when high-resolution CT was used as the reference standard. 18F-PET and 18F-FDG-PET-CT appear to accurately detect muscle inflammation, although correlations with clinical measures of IIM disease activity were variable. [18F] florbetapir PET-CT and [11C] PIB PET were able to differentiate sporadic inclusion body myositis (IBM) from non-IBM IIM.


CONCLUSION
PET-CT holds promise as a single tool that can simultaneously evaluate multiple aspects of IIM. These include screening for associated malignancy, achieving an early diagnosis of ILD and evaluating muscle inflammation.