Musculoskeletal changes on [18F]FDG PET/MRI from complex regional pain syndrome in foot.

94 Objectives: Complex regional pain syndrome (CRPS) is a debilitating chronic pain condition mostly affecting limbs, with 50,000 new cases every year in the U.S (1). Typical CRPS symptoms are similar to those of peripheral nerve injury, but the standard electrodiagnostic methods for identifying nerve injury are usually unacceptable to CRPS patients due to the invasive nature of the test since it can significantly exacerbate pain symptoms in CRPS patients. Recently, a novel [18F]FDG PET/MRI approach has shown promising results in non-invasively detecting painful nerve injury and associated muscle changes in both animal and human studies (2). Our objective is to evaluate the feasibility of [18F]FDG PET/MRI for detecting early musculoskeletal changes due to CRPS. Methods: We conducted our imaging study on seven foot CRPS patients. Enrolled patients were confirmed to have CRPS by matching their symptoms against the Budapest criteria (3). A GE SIGNA PET/MRI system (time-of-flight PET; 3.0T MRI bore) was used for the whole-body PET/MRI scans consisting of eight to ten stations. The injection dose of [18F]FDG was 10mCi, and imaging started one hour after the injection. Metabolic (PET) and anatomic (MRI) abnormalities were identified with radiologic review. The detected lesions were classified into three tissue types (muscle, neurovascular bundle, skin). We performed the two-tailed Mann-Whitney U-test to test the significance of the SUVmax in detected lesions in comparison with the corresponding measurements from 7 healthy controls. Results: From the [18F]FDG PET images, lesions with high [18F]FDG uptake were found in foot muscles (5 patients), neurovascular bundles (3 patients), and skin (2 patients) as shown in Table 1. However, the lesions were much less frequently found in the MRI images (No muscle lesions, neurovascular bundle lesions in 1 patient, skin lesions in 2 patients). The mean and standard deviation of SUVmax from the muscular / neurovascular / skin lesions were 1.49±0.50 / 1.40±056 / 3.10±2.97 while corresponding SUVmax from controls were 0.86±0.19 / 0.6±0.05 / 0.4±0.08. The p-values from the U-test were 0.013 (muscular lesion) and 0.0009 (neurovascular lesion). The p-value of the skin lesions was unavailable due to a small sample size. Figure 1 presents an example of PET/MRI abnormalities on different tissues: high [18F]FDG uptake in dorsal foot muscle (A), high [18F]FDG uptake in thickened subcutaneous tissues (B), high [18F]FDG uptake on the tibial nerve surrounded by scar tissue (C), and globally increased [18F]FDG uptake on femoral, popliteal, and tibial neurovascular bundles (D). Conclusions: In this study, we investigated the feasibility of [18F]FDG PET/MRI to examine musculoskeletal changes by CRPS. Our results showed improved sensitivity of [18F]FDG PET/MRI over the conventional MRI examination. In most patients, focally increased metabolism was observed on the affected muscles without any MR abnormalities. It may suggest the sensitivity of [18F]FDG PET to early changes before the onset of irreversible muscle or skin atrophy. Also, the existence of global metabolic abnormalities may suggest that multiple CRPS subtypes with different etiologies could be responsible for similar clinical manifestations. For example, high [18F]FDG uptake on multiple neurovascular bundles may be exploited to differentiate CRPS into a specific subtype as a surrogate marker for a potential autoimmune component of CRPS, which is being increasingly attributed to one of the causes of CRPS. Acknowledgement: NIH P41 EB015891, GE Healthcare.