Sub-classification of apraxia of speech in patients with cerebrovascular and neurodegenerative diseases

Abstract Some studies have hypothesized that primary progressive apraxia of speech (ppAOS) consists of heterogeneous symptoms that can be sub-classified; however, no study has classified stroke-induced AOS (sAOS) and ppAOS according to common criteria. The purpose of this study was to elucidate the symptoms and relevant brain regions associated with sAOS and ppAOS for sub-classification. Participants included 8 patients with sAOS following lesions in the left precentral gyrus and/or underlying white matter, and 3 patients with ppAOS. All patients with sAOS could be classified into three subtypes: type I, with prominent distorted articulation; type II, with prominent prosodic abnormalities or type III, with similarly distorted articulation and prosodic abnormalities. This sub-classification was consistent with the subtypes of ppAOS proposed in previous reports. All patients with ppAOS were classified as type III, and exhibited three characteristics distinguishable from those of sAOS. First, they showed prominent lengthened syllables compared with the segmentation of syllables. Second, they could not always complete the production of multi-syllabic single words in one breath. Finally, they showed dysfunctional lesions in the bilateral supplementary motor area. We conclude that sAOS and ppAOS can be sub-classified and are universal symptoms that are common between the English and Japanese populations.