Multiparametric magnetic resonance imaging and positron emission tomography findings in the diagnosis of primary progressive aphasia – A case based approach and review of literature

Introduction: Primary progressive aphasia (PPA) is considered a heterogeneous syndrome, with different clinical subtypes and neuropathological causes. Based on clinical, neuroimaging, and neuropathology, PPA is classified into 3 subtypes: non-fluent (nfvPPA) with agrammatism or apraxia of speech, semantic (svPPA) with a progressive and selective loss of lexical semantics, and logopenic (lvPPA) with frequent word-finding pauses and phonemic paraphasias. However, classification is complicated, and some individuals do not fit into one subtype. The svPPA shows association with FTLD-TDP-43, nfvPPA with FTLD-tau pathologies and lvPPA develops into AD.

Neuroimaging is an essential tool for the early diagnosis of PPA in both clinical and research settings. Structural, functional, and metabolic imaging modalities, including magnetic resonance imaging (MRI) and positron emission tomography (PET), are widely available.

This educational exhibit will focus on the complementary role of various imaging modalities, the qualitative and quantitative utility of newer MRI techniques, novel radiopharmaceuticals, and integrated PET/MRI in the setting of PPA.

Methods: To provide neuroimaging characteristics of PPA to understand their pathophysiology and provide an accurate diagnosis.

Help familiarize neuroradiologists with integrated PET/MR imaging in evaluating and diagnosing PPA and its subtypes.

Results: The clinical diagnosis of a specific variant has been associated with a relatively distinct neuroimaging pattern.

MRI- In svPPA, asymmetrical atrophy in the left anterior temporal lobe and hippocampus progresses to the posterosuperior temporal lobe, orbitofrontal, and cingulate cortices. In nfvPPA, atrophy primarily involves the left frontal operculum, insula, Broca's area, basal ganglia, and thalamus. In lvPPA, atrophy initially includes left posterior-perisylvian and later involves ipsilateral parietal-frontal and contralateral temporal lobes. FDG-PET has excellent diagnostic performance (sensitivity 87.8%, specificity 89.9%) in differentiating PPA patients from controls. In svPPA, hypometabolism involves the temporal lobe, entorhinal, perirhinal cortex, inferior temporal poles, and amygdala. In nfaPPA, hypometabolism involves the left inferior frontal and superior temporal regions. lvPPA shows left-sided hypometabolism involving lateral frontal, posterior-lateral temporal lobe, caudate, PCG, and precuneus. Amyloid-PET may be especially useful in lvPPA due to its frequent association with amyloid pathology. Tau-PET correlates with disease severity, atrophy, and FDG hypometabolism.

Conclusions: Multiparametric magnetic resonance imaging and positron emission tomography with FDG, amyloid and tau tracers help in the diagnosis of primary progressive aphasia and their subtypes.

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