Background Although the utility of [¹⁸F] fluoro-deoxy-glucose-positron emission tomography/computed tomography ([¹⁸F] FDG-PET/CT) in the management of rheumatic or inflammatory diseases has been increasingly reported, its applications and benefits in the management of polymyositis (PM)/dermatomyositis (DM) are still controversial [1,2].

Objectives This study aimed to determine whether [¹⁸F] FDG-PET/CT discriminates PM/DM from non-muscular diseases and also whether the FDG uptake in proximal muscles reflects the activity and severity of muscular inflammation in PM/DM.

Methods Twenty treatment-naïve PM/DM patients who underwent [¹⁸F] FDG-PET/CT were retrospectively identified by reviewing medical records. The same number of age- and sex-matched control patients with non-muscular diseases were also identified. Standardized uptake value (SUV) was calculated for each of the seven proximal muscles. For patient-based assessment, mean proximal muscle SUV was calculated by averaging the SUVs for these proximal muscles bilaterally.

Results Mean proximal muscle SUVs were significantly greater in PM/DM patients than those in control patients (median 1.05 vs. 0.69, P < 0.001). Mean proximal muscle SUVs significantly correlated with mean proximal manual muscle test scores (rho = -0.48, P = 0.028) and serum levels of creatine kinase (rho = 0.54, P = 0.015) and aldolase (rho = 0.64, P = 0.002). Furthermore, SUVs in proximal muscles from which biopsy specimens were obtained significantly correlated with the histological grades for inflammatory cell infiltration (rho = 0.66, P = 0.002).

Conclusions Our results suggest that [¹⁸F] FDG-PET/CT is useful in the diagnosis of PM/DM when inflammation in proximal muscles is globally assessed with quantitative measures. Our results also indicate that the local FDG uptake in a proximal muscle reflects the activity of inflammation in the same muscle and provides useful information in determining the region for muscle biopsy.

References

1. Pipitone N, Versari A, Zuccoli G, et al. 18F-Fluorodeoxyglucose positron emission tomography for the assessment of myositis: a case series. Clin Exp Rheumatol 2012;30:570-3.

2. Owada T, Maezawa R, Kurasawa K, Okada H, Arai S, Fukuda T. Detection of inflammatory lesions by f-18 fluorodeoxyglucose positron emission tomography in patients with polymyositis and dermatomyositis. J Rheumatol 2012;39:1659-65.

Disclosure of Interest None Declared