Case report where 18F‑Flortaucipir PET showed asymmetric basal ganglia uptake in an amyloid‑negative patient with corticobasal syndrome, supporting a 4R tauopathy phenotype and suggesting expanded utility of this tracer beyond its current FDA indication.

Supports use of tau PET as a diagnostic biomarker in 4R tauopathies associated with atypical parkinsonism, which could improve patient selection and outcome measures for tau‑targeted therapeutic development.

A 76-year-old woman presented with progressive left-sided motor incoordination, dystonia, and instability, clinically concerning for atypical parkinsonism. MRI showed Fazekas grade 1 chronic microvascular changes. ¹⁸F-FDG brain PET revealed asymmetric right cerebral hemisphere, sensorimotor cortex, and basal ganglia hypometabolism, suggestive of corticobasal degeneration. ¹⁸F-Florbetapir PET was negative. ¹⁸F-Flortaucipir PET demonstrated asymmetric right basal ganglia uptake, corresponding to hypometabolic regions and contralateral to left-sided symptoms. Although ¹⁸F-Flortaucipir demonstrates limited affinity for pure 4R tau and known off-target subcortical binding, the pronounced asymmetry in this Aβ-negative case of atypical parkinsonism supports a 4R tauopathy phenotype, illustrating potential utility beyond the current FDA-approved indication.