Delayed progressive apraxia of speech: A novel clinical entity distinct from primary progressive aphasia - A descriptive case series.

Background: Primary progressive aphasia (PPA) is a neurodegenerative syndrome with language impairment as the initial, predominant symptom. However, speech-language impairments emerge later in the disease course in a subset of neurodegenerative disorders. We introduce the term delayed progressive aphasia (DPA) to describe this subset. Within DPA, we further define delayed progressive apraxia of speech (DPAOS), characterized by isolated apraxia of speech (AOS) without aphasia.

Methods: We retrospectively reviewed patients with neurodegenerative diseases who developed speech-language impairment following an initial phase without speech or language symptoms. Six patients met the criteria for DPA and were compared with 11 patients exhibiting the nonfluent/agrammatic variant of PPA (naPPA), all of whom exhibited AOS. Disease duration since speech-language symptom onset was matched between groups. Neuropsychological performance was compared using Bayesian linear regression analysis.

Results: All six patients who met the criteria for DPA exhibited isolated AOS without any aphasic symptoms. Accordingly, these cases were included in the DPAOS group. The Apraxia of Speech Rating Scale-3 scores were significantly lower in the DPAOS group than in the naPPA group, indicating milder AOS in the former. In the naPPA group, most patients exhibited more severe AOS, and several also showed agrammatism or anomia.

Conclusions: DPAOS represents a clinically distinct presentation of progressive AOS that emerges after other neurological symptoms and remains relatively mild and isolated. Despite possible overlap in underlying pathology, DPAOS and naPPA differ in clinical course and speech-language impairment severity. This distinction may aid early detection of progressive speech disorders in certain neurodegenerative conditions.