[18F]FDG-PET/CT in Idiopathic Inflammatory Myopathies: Retrospective Data from a Belgian Cohort

Abstract

[¹⁸F]FDG-PET/CT is a useful tool for diagnosis and cancer detection in idiopathic inflammatory myopathies (IIMs), especially polymyositis (PM) and dermatomyositis (DM). Data deriving from Europe are lacking. We describe [¹⁸F]FDG-PET/CT results in a Belgian cohort with IIMs, focusing on patients with PM and DM. All of the cases of IIMs admitted between December 2010 and January 2023 to the Cliniques Universitaires Saint-Luc (Belgium) were retrospectively reviewed. In total, 44 patients were identified with suspected IIMs; among them, 29 were retained for final analysis. The mean age of the retained patients was 48.7 years; 19 patients were female (65.5%). Twenty-two patients had DM and seven had PM. The mean serum creatinine kinase (CK) and the mean CRP levels were 3125 UI/L and 30.3 mg/L, respectively. [¹⁸F]FDG-PET/CT imaging was performed for 27 patients, detecting interstitial lung diseases (ILDs) in 7 patients (25.9%), cancer in 3 patients (11.1%), and abnormal muscle FDG uptake compatible with myositis in 13 patients (48.1%). All of the patients who were detected to have ILDs via PET/CT imaging were confirmed using a low-dose lung CT scan. Among the patients who were detected to have abnormal muscle FDG uptake via PET/CT scans (13/28), the EMG was positive in 12 patients (p = 0.004), while the MRI was positive in 8 patients (p = 0.02). We further observed that there was a significantly higher level of CK in the group with abnormal muscle FDG uptake (p = 0.008). Our study showed that PET/CT is useful for detecting cancer and ILDs. We showed that the detection of abnormal muscle uptake via PET/CT was in accordance with EMG and MRI results, as well as with the mean CK value, and that the presence of dyspnea was significantly associated with the presence of ILDs detected via PET/CT imaging (p = 0.002).

Keywords: [18F]FDG-PET/CT; cancer; dermatomyositis; idiopathic inflammatory myopathies (IIMs); interstitial lung disease; polymyositis.

Figure 1

Study flowchart.

Figure 2

Maximum intensity projection (MIP) PET image (A) and coronal FDG-PET, CT, and fused PET/CT images (B) showing a heterogeneously increased muscular FDG uptake, multiple hypermetabolic mediastinal lymphadenopathies, and splenic hypermetabolism in a patient with dermatopolymyositis. (C) Transaxial FDG-PET, CT, and fused PET/CT images showing slightly hypermetabolic pulmonary nodular condensations (arrow) and non-hypermetabolic subpleural reticulations (arrowhead). Furthermore, heterogeneously increased muscle uptake is present in the context of dermatomyositis.

Figure 3

Maximum intensity projection (MIP) PET image (A), transaxial (B), and coronal (C) FDG-PET, CT, and fused PET/CT images demonstrating multiple hypermetabolic mediastinal lymphadenopathies (arrow) and bone lesions (arrowhead) in a patient with lung cancer. Furthermore, a slightly increased cutaneous FDG uptake was observed at the right lumbar region (asterisk). Cutaneous biopsies confirmed the diagnosis of dermatomyositis.

Figure 4

Comparison of mean CK values (UI/L) at diagnosis between PET-negative (no muscle uptake on PET/CT) and PET-positive (abnormal muscle uptake on PET/CT) IIM patients. ** p = 0.008.