Primary progressive apraxia of speech: from recognition to diagnosis and care

Background: Apraxia of speech (AOS) can be caused by neurodegenerative disease and sometimes is its presenting sign (i.e., primary progressive apraxia of speech, PPAOS). During the last several decades, our understanding of PPAOS has evolved from clinical recognition to a fuller understanding of its core and associated clinical features, its distinction from but relationship with primary progressive aphasia, its temporal course and eventual progression to include other neurological deficits, and its neuroimaging correlates and underlying pathology. Aims: This paper provides a comprehensive summary of the literature that has built the current knowledge base about PPAOS and progressive AOS as it co-occurs with progressive aphasia. It reviews the history of its emergence as a recognized syndrome; its relationship with the agrammatic/nonfluent variant of primary progressive aphasia; its salient perceptual features and subtypes; the acoustic and structural/physiological imaging measures that index its presence, severity, and distinction from aphasia; and principles and available data regarding its management and care. Main Contribution: A broad summary of what is known about AOS as a manifestation of neurodegenerative disease. Conclusions: Primary progressive apraxia of speech is a recognizable syndrome that can be distinguished from other neurodegenerative conditions that affect speech and language. AAC: = augmentative and alternative communication; AES = Articulatory Error Score; ALS = amyotrophic lateral sclerosis; AOS = apraxia of speech; AOS+PAA = AOS plus the agrammatic/nonfluent variant of PPA; ASRS = Apraxia of Speech Rating Scale; CBD = corticobasal degeneration; CBS = corticobasal syndrome; DAOS = dominant AOS–aphasia present but AOS more severe; MSD = motor speech disorders; nfPPA = nonfluent variant of PPA, with or without AOS; NVOA = nonverbal oral apraxia; PAOS = progressive AOS, with or without aphasia; PAA = agrammatic variant of PPA, without AOS; PPA = primary progressive aphasia, with or without AOS; PPAOS = primary progressive AOS - no aphasia; PSP = progressive supranuclear palsy; SMA = supplementary motor area.