Acquired AOS is caused by any process or condition that compromises the structures and pathways of the brain responsible for planning and programming motor movements for speech. Causes most often include
- traumatic brain injury (TBI);
- surgical trauma (e.g., tumor resection); or
- neurodegenerative diseases (e.g., corticobasal degeneration, progressive supranuclear palsy)
Occasionally, AOS is the first, only, or most prominent symptom in degenerative conditions. The term primary progressive AOS (PPAOS) is used in such cases (Duffy, 2006; Duffy & McNeil, 2008; Duffy, Peach, & Strand, 2007). Premotor and supplementary motor areas are implicated in progressive forms of AOS (e.g., Josephs et al., 2012).