Neuroimaging in Primary Progressive Aphasia

Neuroimaging is a standard part of a primary progressive aphasia (PPA) diagnostic work-up and an important component of research investigating changes in the speech-language network in patients with PPA. In this paper, structural neuroimaging, including computed tomography (CT), magnetic resonance imaging (MRI), and diffusion tensor imaging (DTI), as well as functional neuroimaging, including single photon emission computed tomography (SPECT), positron emission tomography (PET), and functional MRI (fMRI), are discussed. Neuroimaging, in conjunction with meticulous clinical and neuropsychological evaluation, can increase diagnostic certainty for PPA subtyping and identification of underlying pathology, which is important for justification of potential pharmacological treatments, such as cholinesterase inhibitors. MRI and, more recently, DTI, have expanded our knowledge of structural brain changes in PPA, including gray matter abnormalities as well as alterations in neuronal tracts. SPECT and PET provide information regarding brain regional blood perfusion (SPECT) or metabolism (PET). Recently, thanks to PET ligands that bind to amyloid protein, it has become possible to diagnose or rule out Alzheimer pathology as a cause for PPA and tau imaging may be forthcoming. Finally, fMRI provides a unique window into brain-behavior relations for language as well as reorganization of the language network in disease. fMRI has also been used to gauge the effects of therapeutic interventions, including language treatment, and can be used for implementation of neuromodulatory mediations, such as repetitive transcranial magnetic stimulation (TMS).