18F-Flortaucipir PET/MRI Supports a 4R Tauopathy Phenotype in Corticobasal Degeneration

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.