Muscle fluorodeoxyglucose uptake assessed by positron emission tomography–computed tomography as a biomarker of inflammatory myopathies disease activity

Abstract

Objective To devise a simple PET-CT score for measurement of muscle disease activity in patients with inflammatory myopathies (IMs) and to assess its validity. Methods A total of 44 PET-CT examinations in 34 IM patients (performed during cancer screening) and 20 PET-CT examinations in matched controls (investigated for pulmonary nodules with a conclusion of benignity) were analysed. Maximal standardized uptake values (SUVmax) were recorded bilaterally in eight proximal muscles. The muscle SUVmax (mSUVmax) was defined as the average of the 16 muscle SUVmax values, normalized on the liver mean SUV. Reliability, validity and responsiveness were evaluated. Results The mSUVmax was increased in IM patients compared with controls. This index allowed the identification of patients with high vs low muscle disease activity using the myositis intention to treat activity index as the gold standard. In patients with subsequent examinations, our method showed good accuracy to detect changes in muscle disease activity [area under the curve 0.96 (95% CI 0.84, 1)]. Responsiveness was strong. Interrater reliability was excellent. Conclusion PET-CT, a non-invasive tool useful for cancer screening, is also valuable to measure muscle disease activity and its evolution in IM patients.

MRI and muscle imaging for idiopathic inflammatory myopathies

“…FDG PET imaging also permits to detect muscle inflammation, but normal values for muscle Standardized Uptake Value (SUV) are difficult to define (120)(121)(122)(123). The sensitivity for muscle inflammation is broad: 33-90% (120)(121)(122)124) in IIM depending on muscle inflammation definition (qualitative or quantitative definition). Muscle SUV seems correlated to CK levels and MMT (124,125), and one study found a correlation between inflammation on biopsies and SUV (124).…”

“…When compared to a validated technique for assessment of IIM activity, FDG‐PET showed that muscle FDG uptake measurement has high sensitivity and specificity to distinguish active from non‐active muscle disease and a good sensitivity to detect changes in muscle disease activity (122).…”

Treatment-naïve idiopathic inflammatory myopathy: disease evaluation by fluorodeoxyglucose versus pyrophosphate

“…Previously reported results were similarly ambiguous. Some authors found a correlation between SUV of FDG and myositis severity, muscle strength, and the extent of inflammatory infiltrate in biopsy [25][26][27][28], while others found no correlation of FDG findings with paraclinical or clinical parameters [13,29,30]. The reason may be a heterogeneous disease manifestation as described by Sun et al, who noted that an average SUV is not necessarily representative of the activity and severity of muscles specifically affected in IIM patients [31].…”

F18-FDG PET/CT in a patient with Antisynthetase Syndrome

“…Antisynthetase Syndrome is a rare and poorly defined autoimmune disease associated with interstitial lung disease, polymyositis, and dermatomyositis 1 2 3 4 5 6 . MRI can help differentiating fatty muscle lesions from inflammatory changes; however, the ability to perform a whole-body examination is restricted.…”