PET Scan: Nuclear Medicine Imaging in Myositis

Abstract

Purpose of review: Positron emission tomography (PET) combined with computed tomography (CT) has proven useful as a cancer screening technique in patients with inflammatory myopathy, mainly dermatomyositis. In this review, we focus on advances in this direction and other potential applications of PET/CT in patients with inflammatory myopathy.

Recent findings: Cancer screening by PET/CT seems suitable and cost-effective in patients with myositis. It has also shown value as a hybrid technique for diagnosing myositis versus controls and could be of interest for differentiating between polymyositis and sporadic inclusion body myositis. Quantification of muscle activity by PET/CT seems reliable. Preliminary data suggest that it could also be used to diagnose and measure the activity of the disease in the lung. PET/CT should be in the toolbox of physicians managing patients with myositis. The multiple applications of PET/CT include its value for cancer screening, measuring the activity of the disease in muscle, and helping to differentiate between myositis phenotypes. The possibility to diagnose and monitor inflammatory lung activity remains to be demonstrated in well-designed studies.

Keywords: Activity; Dermatomyositis; Malignancy; Myositis; PET/CT; Sporadic inclusion body myositis.

Fig. 1

A 49-year-old woman presented with the characteristic Gottron sign and heliotrope rash. She reported progressive muscle weakness during the last 2 months. Blind screening with [¹⁸F]-FDG PET/CT (left panel) disclosed a uterine mass yielding a high standardized uptake value (SUV max = 12.8) (arrow). Hysterectomy revealed an undifferentiated uterine sarcoma. The right panel shows [¹⁸F]-FDG PET image

Fig. 2

A 58-year-old man was diagnosed with statin-associated immune-mediated necrotizing myopathy, with positive anti-HMGCR antibodies. Cancer screening with [¹⁸F]-FDG PET/CT (left panel) detected no malignancy but documented high uptake (SUVmax = 3.4) in the proximal muscles (arrows). At the time PET/CT was performed, the creatine kinase value was 49,010 IU/L (normal value, < 195 IU/L). The patient improved after immunosuppressive therapy. The right panel shows normal muscle uptake (arrows) in a patient without myositis

Fig. 3

A man aged 55 years consulted for dyspnoea and mild muscle weakness. On physical examination, mechanic’s hands were observed, and lung crackles were noted at auscultation. He was diagnosed with antisynthetase syndrome and received treatment with tacrolimus and prednisone, achieving a mild improvement. [¹⁸F]-FDG PET/CT performed for cancer screening (left panel) did not detect cancer, but isotope uptake was high in both lung bases (SUV max = 4.5) (arrows). As lungs are normally filled with air, the metabolic index is null and the SUVmax is usually negligible in physiologic conditions. Infectious complications were ruled out. The right panel shows [¹⁸F]-FDG PET image