Posterior Primary Progressive Prosopagnosia: Imaging and Neuropathology

Abstract

AbstractBackgroundProsopagnosia is common with right temporal lesions, often in the fusiform gyrus when caused by vascular pathology. When caused by frontotemporal dementia, the lesion typically begins in the temporal tip. We are reporting advanced imaging, including tau and inflammation, as well as neuropathology in a patient with pathology centered at the posterior extent of the fusiform gyrus.MethodA 69‐year‐old man with apperceptive prosopagnosia and a negative amyloid positron emission tomogram (PET) underwent MRI and PET using 11C‐PBR28, an inflammation tracer, and 18F‐flortaucipir. VT values for 11C‐PBR28 were calculated with the Logan plot and a metabolite‐corrected arterial input function. For 18F‐flortaucipir, the SUV ratio over the cerebellar gray matter was calculated for t = 80‐100 min. A neuropathological examination was conducted using standard procedures as well as phospho‐tau histochemistry.ResultAtrophy and 18F‐flortaucipir uptake involved a similar region at the posterior extent of the right fusiform gyrus and, minimally, a symmetrical region of the left fusiform gyrus and an area in right premotor cortex. Involving the same regions, the 11C‐PBR28 signal was however more extensive than atrophy or 18F‐flortaucipir signal. At autopsy, the patient had corticobasal degeneration (CBD), with severe 4R tau involvement of temporo‐occipital, inferior parietal, and frontal cortices, as well as limbic regions and subcortical nuclei. The location of CBD pathology in this patient was highly atypical, as shown by comparing the neuropathological findings with the findings in two typical CBD patients.ConclusionAlthough prosopagnosia from ischemic and other lesions in the right posterior temporo‐occipital region is common, primary progressive prosopagnosia in the absence of amyloid has been described mostly with involvement of the right anterior temporal region. As exemplified by our patient, it can rarely happen with posterior temporal involvement and in this case the pathology was not TDP‐43 type C, as present in most patients with anterior temporal involvement, but corticobasal degeneration, a 4R tauopathy.