Objective: Objective: To describe the clinical presentation and neuropathology of cases where the degree of tau pathology is mild, and the neuronal loss is anatomically restricted, suggestive of a benign form of Progressive Supranuclear Palsy (PSP).

Background: Background: After Richardson’s syndrome (PSP-RS), asymmetric parkinsonism with tremor is the second most common clinical presentation of PSP, or PSP with predominant-parkinsonism phenotype (PSP-P). PSP-P shows a longer disease duration and tau pathology has less cortical involvement than in PSP-RS.

Method: Methods: From our collection of pathologically confirmed PSP patients we identified patients with the minimal degree of pathology. A retrospective chart review and detailed neuropathology were conducted.

Results: Results: We identified two cases (age of death 73-year-old and 82-year-old) with a mild degree of tau pathology restricted to the substantia nigra, globus pallidus, and subthalamic nucleus associated with moderate nerve cell loss suggestive of an early stage-1 transition to stage-2 of the recently described 6-stages of PSP pathology [1]. Tau pathology was milder than in previously reported PSP-P cases. There was a lack of significant co-pathology including Lewy bodies. Unexpectedly, the disease duration was 9 and 12 years and the clinical presentation observed was asymmetric parkinsonism with one patient exhibiting an exquisite levodopa-response and levodopa-induced dyskinesia. Of note, none of the two patients received an in-life diagnosis of PSP.

Conclusion: Conclusions: In this report of two patients, a mild degree of restricted tau pathology associated with a long disease duration and a parkinsonism-predominant phenotype. Our observations suggest that in contrast to the more common PSP variants, especially PSP-RS, there is a less widespread form of pathological tau accumulation compatible with a benign PSP. This could be related to a less efficient seeding capacity or cell-to-cell propagation throughout the brain.

References: 1. Kovacs, G.G., Lukic, M.J., Irwin, D.J. et al. Distribution patterns of tau pathology in progressive supranuclear palsy. Acta Neuropathol 140, 99–119 (2020)

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