Objective: To describe two cases of progressive supranuclear palsy (PSP) concomitant with cerebellar ataxia in early stage who underwent [18F]THK-5351 PET imaging and to investigate the correlation between the clinicopathological findings and the [18F]THK-5351 PET imaging in one case.

Background: PSP is one of the tauopathies characterized by abnormal depositions of 4-repeat tau isoforms in the brainstem, basal ganglia, neocortex, and dentate nucleus of the cerebellum. Cerebellar ataxia is sometimes identified in PSP patients, reflecting the neurodegeneration of the cerebellum. [18F]THK-5351 PET imaging was developed to detect those tau depositions, even though recent studies revealed that [18F]THK-5351 binds to MAO-B as an off-target.

Method: Case reports.

Results: The two patients developed progressive postural instability eventually fell frequently in the seventh decade of life. In addition, they manifested cerebellar ataxia in their early stage of the disease. Upon the brain MRI, midbrain atrophy was detected in both patients, and the clinical diagnosis of PSP was made based on the clinical and neuroradiological evaluations. [18F]THK-5351 PET imaging, performed at 6 years after the onset of disease in both patients, showed that increased accumulation in both the midbrain and the globus pallidum as well as in the dentate nucleus of the cerebellum. The laterality of [18F]THK-5351 accumulation in the cerebellum was compatible with the clinical predominancy of cerebellar ataxia. Further, the predominant side of [18F]THK-5351 accumulation in the cerebellum was consistent with the relative hypometabolism side detected by [18F]FDG PET imaging. Histopathological examination, performed 7 years after the onset of the symptoms in one case, revealed that the tau pathology was marked in the midbrain, subthalamic nucleus, and globus pallidum. There were notable tau pathology and grumose degeneration in both the dentate nucleus and the white matter in the cerebellum.

Conclusion: In our comparison between clinicopathological and neuroimaging findings in PSP patients, [18F]THK-5351 accumulation should potentially detect the tau pathology and neurodegeneration, and be useful findings in the differential diagnosis of ataxic disorders such as multiple system atrophy.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/18fthk-5351-pet-imaging-in-progressive-supranuclear-palsy-concomitant-with-cerebellar-ataxia-in-early-stage-clinicopathological-observations/