Chronic apraxia of Speech and “Broca’s Area”
Shruti Sonni, MD
Apraxia of speech (AOS) is a speech impairment characterized by deficits of motor planning and programming of speech articulation. There is currently no consensus regarding the site of lesion that causes AOS. Earlier studies have localized it to an area supplied by the superior division of the left middle cerebral artery (MCA), and more recently to the anterior insula (suggesting a clot in the MCA stem). Gottesman et al. postulated that the insula may not actually be associated with AOS in the acute phase, but more so in recovery. In this study they tested the hypothesis that chronic AOS (lasting more than 12 months) is associated with large lesions involving the insula and Brodmann area 44/45 (Broca’s area).
Thirty-four right-handed English-speaking patients with chronic left sided supratentorial infarcts were enrolled in this study and administered the Apraxia Battery for Adults (ABA II). Their MRI FLAIR sequences were analyzed for location of infarct as well as size by volumetric analysis. Association between impairment on AOS measures and infarct location and volumes were calculated. Interestingly, none of the patients were found to have pure AOS, but rather AOS with some components of Broca’s aphasia (impaired fluency, naming etc.). There was a strong association between lesion volume and AOS on some subtests on the ABA II. Using stringent measures, AOS was found to be associated with left Brodmann area 44 and posterior insula.
Contrary to prior studies, the anterior insula was not associated with AOS in this population. This was explained by damage to the anterior insula in large strokes, suggesting that this was a possible confounder. AOS is difficult to reliably assess, and there is a lot of disagreement among speech language pathologists and neurologists regarding the existence and definition of this entity. In this study, subtle technical distinctions were made in AOS measures and localization, making it difficult to interpret the results clinically. The methodology section noted that patients selected were all English speaking. This raises the question if non English speaking patients have different findings than this population.
This is a good overview of the historical and current perspective on AOS, with well defined criteria for diagnosis. The authors conclude that chronic AOS is associated with larger infarcts, as many different areas are involved in speech praxis, and are capable of compensating for damage to single regions. The most important regions that were found to be associated with chronic AOS, independent of lesion volume, were Broca’s area, anterior temporal cortex and posterior insula, likely key areas in motor speech recovery. The suggested etiology for these lesions was likely embolic, probably from carotid dissection. The clinical significance of this paper is that patients with large left MCA strokes will probably benefit from early introduction of speech therapy and language rehabilitation. Further studies are needed for a convincing localization of speech praxis.