Global aphasia without hemiparesis: the underlying mechanism examined by transcranial magnetic stimulation.

Introduction: Global aphasia without hemiparesis (GAWH) is a rare stroke syndrome. Using transcranial magnetic stimulation (TMS), we evaluated 2 possible pathogenic mechanisms for GAWH: sparing of the decussated pyramidal tract, or alternatively, compensation by the ipsilateral pyramidal tract.

Methods: Six patients were diagnosed to have GAWH by the Standard Language Test of Aphasia for Japanese. All patients underwent brain magnetic resonance (MR) imaging and angiography. According to the Trial of Org 10172 in Acute Stroke Treatment (TOAST) criteria, stroke subtype was determined as 3 patients with cardioembolic stroke, 2 with large-artery atherosclerosis, and 1 with another type. All patients underwent TMS, using a figure-of-8 coil, from 3 to 12 months after the onset, and motor evoked potentials were recorded on the abductor digiti minimi muscles.

Results: All patients had left-sided frontal or temporal lesions that were confirmed by MR diagnostic imaging. No motor evoked potential could be recorded by ipsilateral TMS. In 3 patients, brain stimulation on either side evoked the same amplitude on the contralateral abductor digiti minimi, whereas in the other 3 patients, the amplitude was suppressed on the right side. The infarction in the former patients was caused by cardioembolism and in the latter was not. In serial slices of brain MR imaging, the pyramidal tract was spared in the former and was involved to various degrees in the latter 3 patients.

Conclusions: We recommend that GAWH was caused by the sparing of the decussated pyramidal tract. The pyramidal tract was intact in cases of GAWH caused by cardioembolism and subclinically impaired by other causes.