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.

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We report a case of a 69-year-old woman with primary hyperoxaluria type I, who developed a severe hypercalcemia despite controlled secondary hyperparathyroidism. Bone scintigraphy showed diffuse increased uptake in axial and peripheral skeleton. 18F-FDG PET/CT showed countless striking hypermetabolic foci, interesting 2 types of lesions (joint calcifications and periosteal resorptions). Bone biopsy demonstrated inflammatory changes around many calcium oxalate crystals; hypercalcemia was then related to oxalate osteopathy. Immunotherapy with denosumab was thus initiated. Eighteen months later, a second PET/CT showed decreased 18F-FDG uptake, reflecting treatment efficacy on inflammatory reaction secondary to calcium oxalosis skeletal deposits.

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Post-transplant lymphoproliferative disorder (PTLD) is a rare complication of immunosuppression. Sequential treatment is commonly proposed, combining induction with rituximab (R-induction) followed by either continuation of treatment or addition of chemotherapy depending on response. Response to R-induction, often assessed by CT scan, is a major predictor of overall survival (OS). The aim of the study was to analyze predictive factors of R-induction response, including total metabolic tumor volume (TMTV), and investigate the role of 18F-FDG PET/CT in response assessment. This retrospective multicenter study is based on patients with PTLD included in the K-VIROGREF cohort. Only patients treated by R-induction with a baseline 18F-FDG PET/CT were included. Response to R-induction was assessed by 18F-FDG PET/CT. The optimal threshold of TMTV for rituximab response was determined using receiver operating characteristic curves. Univariate and multivariate analyses were conducted to identify predictive factors of response. A total of 67 patients were included. Survival characteristics were similar to those previously reported: the complete response rate to R-induction was 30%, the 3-year OS estimate was 66%, and the treatment-related mortality was 4%. The optimal threshold for TMTV to predict R-induction response was 135 cm3. The response rate to R-induction was 38% in the 21 patients with TMTV ≥ 135 cm3 and 72% in the 46 patients with TMTV < 135 cm3. TMTV was a significant predictor of response, both at univariate and multivariate analyses (odd ratios = 3.71, P = 0.022). Baseline TMTV is predictive of response to R-induction. Early assessment of patient response is feasible with 18F-FDG PET/CT.

BackgroundThere is a need for tools to measure muscle disease activity in inflammatory myopathies (IM).ObjectivesTo assess the contribution of metabolic imaging with positron emission tomography combined with computed tomography (PET-CT) 18F fluorodeoxyglucose-(18F-FDG) for muscle disease activity assessment in patients with IM.MethodsThe SMGM was higher in IM than in the control group in visual analysis (p<0.001) and quantitative analysis (p<0.001). No correlation was found between the SMGM and the muscle histological findings. In addition, the quantitative measurement of SMGM was significantly correlated with serum CK levels (Spearman ρ=0.47, p<0.01) and with the MITAX (Spearman ρ=0.72; p=0.001). Finally, in 9 patients who underwent two consecutive 18F-FDG PET-CT, the evolution of the SMGM was concordant with the clinical course according to the MITAX in 8.ResultsThe SMGM was higher in IM than in the control group in visual analysis (p<0.001) and quantitative analysis (p<0.001). No correlation was found between the SMGM and the muscle histological findings. In addition, the quantitative measurement of SMGM was significantly correlated with serum CK levels (Spearman ρ=0.47, p<0.01) and with the MITAX (Spearman ρ=0.72; p=0.001). Finally, in 9 patients who underwent two consecutive 18F-FDG PET-CT, the evolution of the SMGM was concordant with the clinical course according to the MITAX in 8.ConclusionsThese data suggested that 18F-FDG PET-CT, which is useful for the screening of cancer associated IM, is also helpful for the measurement of IM muscle disease activity.Disclosure of InterestNone declared