Akinetic Mutism Following Unilateral Anterior Cerebral Artery Occlusion

SIR: Since the initial description of akinetic mutism in 1931, lesions in a variety of locations have been associated with this and other disorders of diminished motivation.¹ Akinetic mutism, the most severe of these disorders, is most commonly associated with bilateral hemispheric pathology,² although unilateral lesions may produce this condition as well.³ We describe a man with akinetic mutism due to an ischemic stroke in the distribution of the left anterior cerebral artery. This report may offer additional insight into the mechanism of akinetic mutism following unilateral hemispheric injury.

Case Report

Our patient is a 61-year-old right-handed man who presented to the emergency department with an acute onset of right-leg weakness. During the course of several hours, his weakness progressed to include his right arm; and he stopped speaking. On examination, he was alert but produced no spontaneous speech and had only rare, spontaneous movement of his nonparetic left arm and leg. With repeated prompting, he followed single-step commands, using only his left side.

An arteriogram demonstrated occlusion of the left anterior cerebral artery. Magnetic resonance imaging, which included diffusion-weighted sequences, was performed 6 days after the onset of symptoms and demonstrated an infarction in the distribution of the left anterior cerebral artery, involving the cingulate gyrus and the left half of the corpus callosum.

During the course of several weeks, as the patient became more interactive, he demonstrated normal language function and some improvement in his right hemiparesis. As he became more communicative, right hemineglect became apparent. Despite these improvements, the patient remained apathetic and functionally disabled and was transferred to a rehabilitation facility for further care.

Comment

To our knowledge, this case is the first in vivo description of acute akinetic mutism produced by a unilateral infarction of the cingulate gyrus in combination with disconnection of the contralateral cingulate gyrus due to hemi-infarction of the corpus callosum. The syndrome of akinetic mutism is typically the result of bilateral hemispheric injury, usually involving the anterior cingulate gyri.² Other locations for lesions producing akinetic mutism include the thalami, globus pallidus, internal capsule, and frontal white matter.³ These lesions are thought to disrupt anterior frontal subcortical circuits that subserve motivation.⁴ In our patient, the syndrome of akinetic mutism appears to be the result of a lesion in the body of the cingulate gyrus in one hemisphere in combination with the extension of the stroke into the body of the corpus callosum, effectively disconnecting the functional contralateral cingulate gyrus. In effect, this unilateral lesion disrupted bilateral pathways that are necessary in order to sustain normal motivation.

The involvement of bilateral callosal fibers in the regions of the anterior cingulate may also explain the profound hemineglect that emerged as the akinetic mutism improved. The anterior cingulate cortex is part of a bihemispheric network of cortical, subcortical, and white matter structures that are involved in attention, including spatial attention.⁵ The left cingulate lesion and callosal disconnection may have sufficiently disrupted the patient's spatial attention network such that right visual neglect and anosognosia resulted.