Objective:To compare the rate of abnormal brain metabolism by FDG-PET/CT to other paraclinical findings and to describe brain metabolism patterns in autoimmune encephalitis (AE).Methods:A retrospective review of clinical data and initial dedicated brain FDG-PET/CT studies for neurology inpatients with AE, per consensus criteria, treated at a single tertiary center over 123 months. Z-score maps of FDG-PET/CT were made using 3-dimensional stereotactic surface projections with comparison to age group–matched controls. Brain region mean Z-scores with magnitudes ≥2.00 were interpreted as significant. Comparisons were made to rates of abnormal initial brain MRI, abnormal initial EEG, and presence of intrathecal inflammation.Results:Sixty-one patients with AE (32 seropositive) underwent brain FDG-PET/CT at median 4 weeks of symptoms (interquartile range [IQR] 9 weeks) and median 4 days from MRI (IQR 8.5 days). FDG-PET/CT was abnormal in 52 (85%) patients, with 42 (69%) demonstrating only hypometabolism. Isolated hypermetabolism was demonstrated in 2 (3%) patients. Both hypermetabolic and hypometabolic brain regions were noted in 8 (13%) patients. Nine (15%) patients had normal FDG-PET/CT studies. CSF inflammation was evident in 34/55 (62%) patients, whereas initial EEG (17/56, 30%) and MRI (23/57, 40%) were abnormal in fewer. Detection of 2 or more of these paraclinical findings was in weak agreement with abnormal brain FDG-PET/CT (κ = 0.16, p = 0.02).Conclusions:FDG-PET/CT was more often abnormal than initial EEG, MRI, and CSF studies in neurology inpatients with AE, with brain region hypometabolism the most frequently observed.
Diagnosis of autoimmune encephalitis presents some challenges in the clinical setting because of varied clinical presentations and delay in obtaining antibody panel results. We examined the role of neuroimaging in the setting of autoimmune encephalitides, comparing the utility of 18 F-FDG PET/CT versus conventional brain imaging with MRI. Methods: A retrospective study was performed assessing the positivity rate of MRI versus 18 F-FDG PET/CT during the initial workup of 23 patients proven to have antibody-positive autoimmune encephalitis. 18 F-FDG PET/CT studies were analyzed both qualitatively and semiquantitatively. Areas of cortical lobar hypo (hyper)-metabolism in the cerebrum that were 2 SDx from the mean were recorded as abnormal. Results: On visual inspection, all patients were identified as having an abnormal pattern of 18 F-FDG uptake. In semiquantitative analysis, at least 1 region of interest with metabolic change was identified in 22 of 23 (95.6%) patients using a discriminating z score of 2. Overall, 18 F-FDG PET/ CT was more often abnormal during the diagnostic period than MRI (10/23, 43% of patients). The predominant finding on brain 18 F-FDG PET/CT imaging was lobar hypometabolism, being observed in 21 of 23 (91.3%) patients. Hypometabolism was most commonly observed in the parietal lobe followed by the occipital lobe. An entire subset of antibody-positive patients, anti-N-methyl-D-aspartate receptor (5 patients), had normal MRI results and abnormal 18 F-FDG PET/CT findings whereas the other subsets demonstrated a greater heterogeneity. Conclusion: Brain 18 F-FDG PET/CT may play a significant role in the initial evaluation of patients with clinically suspected antibody-mediated autoimmune encephalitis. Given that it is more often abnormal when compared with MRI in the acute setting, this molecular imaging technique may be better positioned as an early biomarker of disease so that treatment may be initiated earlier, resulting in improved patient outcomes.
Objective:To compare brain metabolism patterns on fluorodeoxyglucose (FDG)-PET/CT in anti–NMDA receptor and other definite autoimmune encephalitis (AE) and to assess how these patterns differ between anti–NMDA receptor neurologic disability groups.Methods:Retrospective review of clinical data and initial dedicated brain FDG-PET/CT studies for neurology inpatients with definite AE, per published consensus criteria, treated at a single academic medical center over a 10-year period. Z-score maps of FDG-PET/CT were made using 3-dimensional stereotactic surface projections in comparison to age group–matched controls. Brain region mean Z scores with magnitudes ≥2.00 were interpreted as significant. Comparisons were made between anti–NMDA receptor and other definite AE patients as well as among patients with anti–NMDA receptor based on modified Rankin Scale (mRS) scores at the time of FDG-PET/CT.Results:The medial occipital lobes were markedly hypometabolic in 6 of 8 patients with anti–NMDA receptor encephalitis and as a group (Z = −4.02, interquartile range [IQR] 2.14) relative to those with definite AE (Z = −2.32, 1.46; p = 0.004). Among patients with anti–NMDA receptor encephalitis, the lateral and medial occipital lobes were markedly hypometabolic for patients with mRS 4–5 (lateral occipital lobe Z = −3.69, IQR 1; medial occipital lobe Z = −4.08, 1) compared with those with mRS 0–3 (lateral occipital lobe Z = −0.83, 2; p < 0.0005; medial occipital lobe Z = −1.07, 2; p = 0.001).Conclusions:Marked medial occipital lobe hypometabolism by dedicated brain FDG-PET/CT may serve as an early biomarker for discriminating anti–NMDA receptor encephalitis from other AE. Resolution of lateral and medial occipital hypometabolism may correlate with improved neurologic status in anti–NMDA receptor encephalitis.
ObjectiveRadiotracers targeting prostate-specific membrane antigen (PSMA) have increasingly been recognized as showing uptake in a number of normal structures, anatomic variants, and non-prostate-cancer pathologies. We aimed to explore the frequency and degree of uptake in peripheral ganglia in patients undergoing PET with the PSMA-targeted agent 18F-DCFPyL.MethodsA total of 98 patients who underwent 18F-DCFPyL PET/CT imaging were retrospectively analyzed. This included 76 men with prostate cancer (PCa) and 22 patients with renal cell carcinoma (RCC; 13 men, 9 women). Scans were evaluated for uptake in the cervical, stellate, celiac, lumbar and sacral ganglia. Maximum standardized uptake value corrected to body weight (SUVmax), and maximum standardized uptake value corrected to lean body mass (SULmax) were recorded for all ganglia with visible uptake above background. Ganglia-to-background ratios were calculated by dividing the SUVmax and SULmax values by the mean uptake in the ascending aorta (Aortamean) and the right gluteus muscle (Gluteusmean).ResultsOverall, 95 of 98 (96.9%) patients demonstrated uptake in at least one of the evaluated peripheral ganglia. With regard to the PCa cohort, the most frequent sites of radiotracer accumulation were lumbar ganglia (55/76, 72.4%), followed by the cervical ganglia (51/76, 67.1%). Bilateral uptake was found in the majority of cases [lumbar 44/55 (80%) and cervical 30/51 (58.8%)]. Additionally, discernible radiotracer uptake was recorded in 50/76 (65.8%) of the analyzed stellate ganglia and in 45/76 (59.2%) of the celiac ganglia, whereas only 5/76 (6.6%) of the sacral ganglia demonstrated 18F-DCFPyL accumulation. Similar findings were observed for patients with RCC, with the most frequent locations of radiotracer uptake in both the lumbar (20/22, 90.9%) and cervical ganglia (19/22, 86.4%). No laterality preference was found in mean PSMA-ligand uptake for either the PCa or RCC cohorts.ConclusionAs PSMA-targeted agents become more widely disseminated, the patterns of uptake in structures that are not directly relevant to patients’ cancers must be understood. This is the first systematic evaluation of the uptake of 18F-DCFPyL in ganglia demonstrating a general trend with a descending frequency of radiotracer accumulation in lumbar, cervical, stellate, celiac, and sacral ganglia. The underlying biology that leads to variability of PSMA-targeted radiotracers in peripheral ganglia is not currently understood, but may provide opportunities for future research.
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