FDG-PET in Autoimmune Cerebellar Ataxia: Clinical Correlation and Diagnostic Superiority Over MRI.

Background: Brain magnetic resonance imaging (MRI) often appears normal in patients with autoimmune cerebellar ataxia (ACA), whereas case studies indicate [¹⁸F]fluoro-2-deoxyglucose (FDG) positron emission tomography (PET) can detect abnormal metabolic patterns in these patients. This study aims to evaluate the brain FDG-PET characteristics of ACA, assess its clinical correlations and diagnostic utility.

Methods: 55 ACA patients and 28 age and sex-matched healthy controls were included. PET results were evaluated using both visual analysis and voxel-based analysis.

Results: Before immunotherapy, FDG-PET of ACA patients typically exhibited widespread hypermetabolism, while post-treatment scans showed cerebellar hypometabolism compared to healthy controls. Patients with encephalopathy were more likely to show abnormal metabolic activity in the cerebral cortex or hippocampus. Abnormal metabolic activity in the basal ganglia was more common in patients with extrapyramidal symptoms. Relative vermis hypermetabolism was observed in 40% of patients (22/55) and was significantly associated with a lower cerebrospinal fluid white blood cell count, higher cerebellar atrophy ratio, and cerebellar hypometabolism. Overall, the sensitivity of FDG-PET (85.5%) was significantly higher than that of MRI (39.1%, p < 0.001).

Conclusion: Our findings demonstrate that FDG-PET is more sensitive than MRI for detecting metabolic abnormalities in ACA patients. The metabolic differences between the cerebellar vermis and the hemispheres may suggest the vulnerability of the vermis in ACA. It also provides valuable clinical correlations, identifying patterns of hyper- and hypometabolism that align with specific neurological presentations.