Objective: To describe a singular case of an early-onset Parkinson disease (PD) patient with PD dementia who presented in vivo positive 18 F-Flutebetamol PET but complete absence of β-amyloid plaques in post-mortem study.

Background: Besides cortical α-synuclein spread, β-amyloid deposition seems to be associated with cognitive decline in PD. Amyloid PET imaging helps diagnostic accuracy, presenting  high sensitivity (97.9%) and specificity (88.9%), and a high negative predictive value, making this test a valid in vivo surrogate of amyloid deposition.

Method: We present the case of a male with early-onset PD at the age of 45, who developed dysautonomia, motor fluctuations and subcortical cognitive impairment with hallucinations after 10 years of diagnosis.

Results: At diagnosis, NGS panel showed a VUS in heterocygosis c.601C>T in the ATP13A2 gen, suggested to enhance the susceptibility of early-onset PD[MSE1] . Brain MRI showed no abnormalities. 18F-FDG PET evidenced bilateral parieto-temporo-occipital hypometabolism and 18F-Flutebetamol PET displayed diffuse intense amyloid deposition, including brainstem and basal ganglia (Fig 1). Due to aggressive evolution, patient died at the age of 66 because of bronchoaspiration pneumonia. Post-mortem neuropathological study showed no β-amyloid plaques deposition in cortex or basal ganglia, neither cerebral amyloid angiopathy, with evidence of neocortical Lewy pathology (Lewy Pathology Consensus, 2021) (Fig 1).

Conclusion: This rare case could represent a lower sensitivity of PET amyloid in non-Alzheimer disease dementia, constituting an exceptional false positive, or we hypothesize the binding of the radiotracer to another protein.

Acknowledgement

The samples used in this project were provided by the Vall d’Hebron University Hospital Biobank with appropriate ethics approval. The authors thank the family for the selfless donation for research purposes.

References: 1. Osama Sabria, Marwan N. Sabbaghb, John Seibylc, Henryk Barthela, Hiroyasu Akatsud,Yasuomi Ouchig et al. Florbetaben PET imaging to detect amyloid beta plaques in Alzheimer’s disease: Phase 3 study. Alzheimer’s & Dementia 11 (2015) 964-974.
2. Christopher M Clark, Michael J Pontecorvo, Thomas G Beach, Barry J Bedell, R Edward Coleman, P Murali Doraiswamy et al. Cerebral PET with florbetapir compared with neuropathology at autopsy for detection of neuritic amyloid-β plaques: a prospective cohort study. Lancet Neurol 2012; 11: 669–78.
3. Kolanko MA, Win Z, Loreto F, et al Amyloid PET imaging in clinical practice Practical Neurology 2020;20:451-462.

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