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Semiquantitative Analysis of Brain Metabolism in Patients With Paraneoplastic Neurologic Syndromes

Purpose The objective of this study was to evaluate brain metabolism with 18F-FDG-PET in patients with definite or possible paraneoplastic neurologic syndromes (PNS) using qualitative assessment and semiquantitative measurements with subsequent correlation with MRI. Methods The institutional review board approved this Health Insurance Portability and Accountability Act–compliant study. A prospective PET database of patients referred for PNS between 2001 and 2010 was queried retrospectively and identified 102 patients who met the diagnostic criteria for PNS, had PET brain imaging, and lacked clinical or MRI evidence of an alternative diagnosis. Qualitative and semiquantitative evaluation of brain metabolism was obtained by 3-dimensional stereotactic surface projection and region-based analysis. Qualitative and semiquantitative assessment was performed blinded to clinical data. Results PET/CT demonstrated that 67 patients had abnormal brain glucose metabolism. Six categories of brain hypometabolism were identified: diffuse (36/67), cerebellar (10/67), basal ganglia (10/67), frontal (9/67), temporal (1/67), and occipital (1/67). The mean Z score of the cerebral cortex in diffuse hypometabolism was 1.65 (range, 0.25–3.46). For cerebellar hypometabolism, the mean Z score of the cerebellum was 2.31 (range, 0.52–4.54). In basal ganglia hypometabolism, the mean Z score was 2.53 (range, 1.78–3.89), and in frontal lobe hypometabolism, the mean Z score was 2.11 (range, 1.39–4.45). The majority (39/67, 62.9%) with abnormal glucose metabolism on PET had a normal MR. Conclusions Patients with PNS frequently have abnormal brain metabolism on semiquantitative PET/CT. With semiquantitative analysis, we defined 6 common patterns of abnormalities, which often correlated with clinical symptoms. Both qualitative and semiquantitative analyses of brain glucose metabolism may be helpful in evaluating PNS, especially in patients with a normal MRI.