Disappearance of long-term right-sided essential tremor after stroke in the left corona radiata

PRACTICAL IMPLICATIONS

Diffusion tensor tractography may help precisely identify the potential target brain area for ET therapy.

Essential tremor (ET) is one of the most common adult-onset movement disorders. It is characterized by postural and action tremor, preferentially involving the upper limbs and sometimes in the lower limbs, head, voice, and trunk. Furthermore, ET is often associated with a positive family history. Thalamotomy and thalamic deep brain stimulation have been successfully used in the treatment of ET. We report the case of a patient with bilateral ET for more than 60 years, with disappearance of the right ET after an infarction in the left corona radiata.

The present study was approved by the Zhongnan Hospital of Wuhan University Ethics Committee, and the patient provided informed consent, authorizing online distribution of the video. The patient was a right-handed man aged 83. He had experienced slowly progressive, bilateral, low-frequency, and action and postural tremors, not involving the head or voice. His father and son were affected by similar tremors. The ET had no effect on his daily life, and therefore, did not require medication in the past. In October 2016, because of 10 years of hypertension, he was hospitalized for sudden onset of mild dysarthria, mild central facial paralysis, and weakness of the right upper and lower limbs. Physical examination revealed a total score of 4 of 5 in the right upper extremity and 4⁺ of 5 in the right lower extremity for muscle strength, and disappearance of the long-term right ET. The National Institute of Health Stroke Scale score was 3 at the time of admission. Stroke workup showed a left corona radiata infarct on MRI (figure, A–C). He was treated with aspirin and statin. After 2 weeks of treatment, the symptoms of neurologic deficits clearly abated and the tremor on the right side did not reappear. In January 2018 (i.e., 15 months after the stroke), the patient was followed up to verify stroke recovery. The results showed full recovery of the mild hemiplegia in the right upper and lower limbs, and the tremor had not reappeared on the right side, whereas the tremor in the left arm and the postural tremor in the left leg remained unchanged. The Mini-Mental State Examination score was 28, and the National Institute of Health Stroke Scale score was 0. An MRI showed only small hypointense T1 signals in the left subcortical corona radiata (figure, D, E), surrounded by hyperintense area in T2-weighted fluid-attenuated inversion recovery sequence (figure, F). To investigate the effect of cerebral infarction on motor nerve fiber bundles, 3-dimensional tensor tractography was performed. The results showed apparent reduction of the corticospinal fibers compared with the contralateral side (figure, G–I). The tremor on the right side did not reappear, as documented on regular follow-ups, the last of which was conducted 2 years after his stoke (video 1).

Figure. MRI.

(A–C) Stroke workup showed a left corona radiata infarct. (D, E) Small hypointense T1 signals in the left subcortical corona radiata (F) surrounded by hyperintense area in T2-weighted fluid-attenuated inversion recovery sequence. (G–I) Apparent reduction of the corticospinal fibers compared with the contralateral side.

Video 1

The video, recorded 2 years after the patient experienced stroke, shows that the tremor in the left arm and the postural tremor in the left leg remained unchanged. However, these were not observed on the right side of the body after he experienced cerebral infarction in the left corona radiata. A more complete description of the patient's examination in the video follows. The arm and leg movements/positions evaluated during the examination include the following: arms or legs at rest, maintaining a posture, and performing an action. Furthermore, dystaxia, gait, and the performance of fine movements were also evaluated.Download Supplementary Video 1 ^{(8.2MB, mp4)} via http://dx.doi.org/10.1212/000650_Video_1

Discussion

The exact pathogenic mechanism of ET remains unknown. Previous studies have shown that ET is associated with alterations in the cerebellothalamocortical network.^1,2 Recently, studies have revealed that the sensorimotor cortex is also involved in the ET; this region is now thought to be the terminal portion of the abnormal cerebellothalamocortical loops.^3,4 Meanwhile, patients have exhibited selective disappearance of the ET after an ischemic lesion affecting the sensorimotor cortex.^5,6 A diffusion tensor imaging study has indicated that patients with ET demonstrate mean and radial diffusivity abnormalities in the tracts involved in primary and associative motor functions.³ However, their association with a specific sensorimotor nerve fiber bundle lesion has not been described previously. The present study indicates that the motor cortex is involved in the pathogenesis of contralateral limb ET. Our findings from three-dimensional tensor tractography suggest that lesions in the posterior part of the inner capsule corticospinal fiber pathway may be the reason for the durability of the resolution of the right-sided ET. Therefore, we speculate that, in ET, the special lesion in the unilateral motor nerve fiber bundle may lead to alterations of the independent oscillator and interrupt the specific tremor-generating network on the opposite side.^4,7 Both deep and noninvasive brain stimulation maybe effective methods for ET therapy, but the target brain areas are different, including the thalamus, posterior cerebellum, and motor cortex. The use of diffusion tensor tractography in our current study as an approach to precisely identify the potential target brain area for ET therapy paves the way for future therapeutic studies. These findings may also be helpful for facilitating further understanding of the neural mechanisms underlying ET.

Author contributions

C. Xi and S. Li: drafting/revising the manuscript, study concept or design, and analysis or interpretation of data. Y. Liu and B. Mei: revising the manuscript, study design, analysis or interpretation of data, and study supervision.

Study funding

This study was supported by the Natural Science Foundation of China (grant number: 81301095).

Disclosure

The authors report no disclosures. Full disclosure form information provided by the authors is available with the Neurology.org/cp.