Peggy Nguyen, MD
Apraxia of speech (AOS) differs from aphasia of speech in that while aphasia denotes an inability to understand and or use language, AOS denotes impairment in the motor initiation and execution needed to produce speech, which leads to impaired speech rate and rhythm and inability to produce the desired speech sound. This neurologic deficit has been poorly localized in the past; to better address this, the authors selected cases of first ever, non-lacunar left MCA ischemic strokes and characterized the location of lesion using voxel based lesion-symptom mapping in patients with AOS versus those without AOS.
In the selected 136 cases, 3 groups were identified: (1) pure AOS n = 7, (2) AOS with aphasia, n = 15, and (3) non-AOS, n = 114. Patients with AOS (both with and without aphasia) had lesions involving the posterior wall of the left precentral gyrus in the central sulcus. Notably, when there was a lesion of the posterior wall of the left precentral gyrus, this was predictive of the presence of AOS in comparison between pure AOS and non-AOS. No brain regions associated with pure AOS were detected, but scattered subcortical brain regions, including basal ganglia and corona radiate were detected in association with AOS-aphasia.
This study builds on the background of the vague neuroanatomical localization of language itself, but does suggest that a lesion in the left precentral gyrus is predictive of the development of AOS. While it may not impact clinical management as of yet, it does lead us to a better neuroanatomical understanding of language. Certainly therapeutic approaches to AOS do differ from aphasia, in that the emphasis lies on teaching rate and rhythm of speech and production of sound as opposed to restoring language ability, and it is conceivable that this may help guide prognosis and therapeutic approaches.