Exploring Neurophysiological Mechanisms and Treatment Efficacies in Laryngeal Dystonia: A Transcranial Magnetic Stimulation Approach

Laryngeal dystonia (LD), known or termed as spasmodic dysphonia, is a rare movement disorder with an unknown cause affecting the intrinsic laryngeal muscles. Neurophysiological studies point to perturbed inhibitory processes, while conventional genetic studies reveal fragments of genetic architecture in LD. The study's aims are to (1) describe transcranial magnetic stimulation (TMS) methodology for studying the functional integrity of the corticospinal tract by stimulating the primary motor cortex (M1) for laryngeal muscle representation and recording motor evoked potentials (MEPs) from laryngeal muscles; (2) evaluate the results of TMS studies investigating the cortical silent period (cSP) in LD; and (3) present the standard treatments of LD, as well as the results of new theoretical views and treatment approaches like repetitive TMS and laryngeal vibration over the laryngeal muscles as the recent research attempts in treatment of LD. Neurophysiological findings point to a shortened duration of cSP in adductor LD and altered cSP duration in abductor LD individuals. Future TMS studies could further investigate the role of cSP in relation to standard laryngological measures and treatment options. A better understanding of the neurophysiological mechanisms might give new perspectives for the treatment of LD.

Treatment of Post-Stroke Dysphagia with Repetitive Transcranial Magnetic Stimulation Based on the Bimodal Balance Recovery Model: A Pilot Study

BACKGROUND

Brain plasticity and functional reorganization are the main mechanisms of stroke rehabilitation and the theoretical basis for transcranial magnetic therapy. Bimodal balance recovery model suggests that the structural integrity of neural pathways affects the functional reorganization mode of brain recovery after stroke. The principal neural pathway that innervates swallowing is the corticobulbar tract (CBT). The goal is to investigate the impact of corticobulbar tract integrity on swallowing function recovery in post-stroke dysphagia (PSD) patients treated with repetitive transcranial magnetic stimulation (rTMS).

METHODS

Thirty-five patients with high CBT integrity (relative fractional anisotropy (rFA) >0.5) and 32 patients with low CBT integrity (rFA ≤0.5) were respectively assigned to three subgroups through a random number table: 5 Hz frequency rTMS group, 1 Hz frequency rTMS group, and Sham rTMS group. The Standardized Swallowing Assessment (SSA), Penetration Aspiration Scale (PAS), and Dysphagia Outcome Severity Scale (DOSS) were analyzed before and after therapy.

RESULTS

Significant improvements in SSA (p < 0.05), PAS (p < 0.05), and DOSS scores (p < 0.05) were seen in the high frequency (HF) and low frequency (LF) groups compared with the Sham group for patients with high CBT integrity. Increased SSA (p < 0.05), PAS (p < 0.05), and DOSS scores (p < 0.05) demonstrated that the HF group achieved greater remediation than the LF and Sham groups for patients with low CBT integrity.

CONCLUSIONS

Both 5 Hz and 1 Hz rTMS over the contralateral hemisphere are effective for the treatment of swallowing disorders for patients with high CBT integrity after stroke; 5 Hz rTMS over the contralateral hemisphere is more effective than 1 Hz and sham stimulation for patients with low CBT integrity.

Diffusion tensor tractography of the corticobulbar tract in a dysphagic patient with progressive supranuclear palsy: A case report

RATIONALE

This paper reports the changes over time in the corticobulbar tract (CBT) analyzed using diffusion tensor tractography (DTT) in a dysphagic patient with progressive supranuclear palsy (PSP).

PATIENT CONCERNS

A 53-year-old man initially presented with dysarthria, gait disturbance, and bradykinesia, and approximately 1-year later, downward gaze paralysis appeared. Initially, there was no dysphagia; however, approximately 2 years after visiting the hospital, symptoms of dysphagia, including difficulty swallowing pills, aspiration, and oral movement impairments appeared. The symptoms gradually progressed, and finally, mouth opening was severely damaged to the extent that it was difficult to orally feed.

INTERVENTIONS

We performed diffusion tensor imaging 3 times; at 3-month, 20-month, and 41-month from onset.

OUTCOMES

On 3-month DTT, the left CBT was well reconstructed, whereas the right CBT showed partial tearing. In the 20-month DTT, both CBTs became thinner compared to the 3-month DTT. On 41-month DTT, both CBTs became much thinner than after 3-month and 20-month DTT.

LESSONS

We observed the degree of CBT injury over time in a dysphagic patient with PSP. These results suggest that the analysis of CBT using DTT is helpful in predicting the degree of dysphagia and prognosis in patients with PSP.

Characterization of stimulus response curves obtained with transcranial magnetic stimulation from bilateral anterior digastric muscles in healthy subjects

PURPOSE

The purpose of the study was to describe measurements of stimulus-response curves in the anterior digastric muscle (ADM) bilaterally following transcranial magnetic stimulation (TMS) to the right and left hemispheres. The first dorsal interosseous muscle (FDI) was the control muscle.

MATERIALS AND METHODS

The subjects were 20 healthy young adults. Test sessions determined motor thresholds (MT) and stimulus-response curves (1.0, 1.2, 1.4, 1.6 × MT) from either the FDI or ADM following TMS to left and right hemispheres using the double cone coil. Bilateral recordings of MEPs in the left and right ADM allowed us to generate stimulus response curves following ipsilateral and contralateral TMS.

RESULTS

Intraclass correlation coefficients (ICC) for MEP amplitudes from ipsilateral and contralateral ADMs were >0.60 at motor threshold (MT) and >0.90 at stimulus intensities above MT. There was a linear increase in MEP amplitudes across stimulus intensities for the FDI following contralateral TMS, while MEP amplitudes from the ADM following contralateral and ipsilateral TMS increased linearly across stimulus intensities [F_{(3, 57) [Muscle × Recording Site × Stim Intensity]} = 33.57; p < 0.05]; (ηp2 = 0.64). The slopes of the stimulus-response curve of the contralateral FDI was greater than the slopes of the stimulus response curves of the ipsilateral and contralateral ADM (p < 0.05).

CONCLUSIONS

The current study provided insights on the methodology for recording stimulus response curves in the ADM with TMS. These findings may translate into a valid, reliable, and relevant clinical outcome to study the pathophysiology of the corticobulbar motor system.

Role of bilateral corticobulbar tracts in dysphagia after middle cerebral artery stroke

BACKGROUND AND PURPOSE

The corticobulbar tract is a potential neural pathway involved in swallowing. The frontal operculum, insular cortex, corona radiata and internal capsule, which are frequently involved in middle cerebral artery (MCA) strokes, are locations in which lesions cause dysphagia. However, it is unclear whether the locations are linked to the corticobulbar tract or whether corticobulbar tract integrity is associated with dysphagia severity. This study aimed to assess the association between corticobulbar tract integrity and dysphagia severity after MCA stroke.

METHODS

Thirty dysphagic patients after MCA stroke and 27 healthy controls were examined. Diffusion tensor imaging (DTI)-derived parameters of the corticobulbar tract were compared between patient and control groups. Next, patients were divided into mild and moderate-to-severe dysphagia groups, and DTI-derived parameters of the corticobulbar tract were compared between the subgroups. Logistic regression analysis was used to determine the association between corticobulbar tract integrity and dysphagia severity.

RESULTS

The tract volume (TV) of the affected corticobulbar tract was lower in dysphagic patients than in healthy controls (P < 0.001). According to dysphagia severity, TV of the unaffected corticobulbar tract was higher in the mild dysphagia group than in the moderate-to-severe dysphagia group (P = 0.012). TV of the unaffected corticobulbar tract was independently associated with dysphagia severity according to the logistic regression model (adjusted odds ratio 0.817, 95% confidence interval 0.683-0.976).

CONCLUSIONS

The corticobulbar tract was affected after MCA stroke and may be associated with dysphagia. A higher corticobulbar TV in the unaffected hemisphere was indicative of better swallowing function in dysphagic patients after MCA stroke.

Recovery of an injured corticobulbar tract in a patient with stroke: A case report

RATIONALE

The corticobulbar tract (CBT) is known to be involved in the motor function of the non-oculomotor cranial nuclei and controls the muscles of the face, head, and neck. Several studies have reported injury of the CBT in patients with brain injury, however, little is known about recovery of the injured CBT.

PATIENT CONCERNS

A 59-year-old right-handed male underwent decompressive craniectomy for management of brain swelling and intracerebral hemorrhage following an infarction in the left middle cerebral artery territory. Initially, the patient had showed severe dysphagia and had to be fed using a Levin tube. Five weeks after the onset of stroke, the patient was transferred to the rehabilitation department and underwent comprehensive rehabilitative therapy. Cranioplasty was performed eight weeks after the onset. The patient was completely recovered from dysphagia and the Levine tube was removed nine weeks after the onset.

INTERVENTIONS

Diffusion tensor imaging was performed twice; at five weeks and nine weeks from the onset.

OUTCOME

On five-week diffusion tensor tractography (DTT), the right CBT was discontinued at the subcortical white matter and showed severe narrowing and the left CBT was not reconstructed. By contrast, on nine-week DTT, the right CBT was extended to the cerebral cortex and thickened while the left CBT remained not reconstructed in DTT.

LESSONS

This case demonstrates the association of the recovery of injured CBT with the recovery of dysphagia using DTT.

Delayed Onset Eye Opening Apraxia due to Progression of Brain Atrophy following Subthalamic Nucleus Deep Brain Stimulation: A Case Report

Eye opening apraxia (EOA) has been described in literature as a complication of deep brain stimulation (DBS), especially after electrode implantation in the subthalamic nucleus (STN). EOA can be either worsened or alleviated by DBS depending on the etiology. Herein, we report a rare case where the progression of brain atrophy may have contributed to the delayed onset of EOA. The patient, a 73-year-old woman, had previously undergone bilateral STN-DBS for advanced Parkinson’s disease (PD), which was performed by another DBS team, at the age of 68 years. She initially experienced a dramatic improvement in her motor symptoms, with no adverse events. However, she had difficulty in opening her right eye 3 years after the DBS surgery. Imaging studies showed that the brain atrophy had progressed over the past 5 years, and that the DBS electrodes were implanted through the far anterior entry points. We considered that the relative movement of the DBS might have been caused by the progression of the brain atrophy to the posterior limb of the internal capsule (IC) where the corticobulbar tract exists, and this was enhanced by the lower implantation angle. The present case illustrates the importance of the DBS insertion angle considering the a+ trophic effect and the follow-up imaging studies after DBS.

Injury of the corticobulbar tract in patients with dysarthria following cerebral infarct: diffusion tensor tractography study

OBJECTIVES

Little is known about injury of the corticobulbar tract (CBT) in stroke patients. We attempted to investigate injury of the CBT in patients with dysarthria following cerebral infarct, using diffusion tensor tractography (DTT).

METHODS

Eight patients with dysarthria following a corona radiata infarct and 12 control subjects were recruited for this study. Diffusion tensor imaging was performed at 14.3 days after onset and reconstruction of the CBT was performed using the probabilistic tractography method. Fractional anisotropy, mean diffusivity, and tract volume of the CBT were measured.

RESULTS

Reconstructed CBTs in the affected hemisphere of the patient group were thinner than those of the unaffected hemisphere of the patient group and the control group. Regarding the DTT parameters of the CBTs, fractional anisotropy and tract volume were significantly lower in the affected hemisphere of the patient group than in the unaffected hemisphere of the patient group and the control group (p < 0.05). However, we did not observe any difference in the mean diffusivity value (p > 0.05).

CONCLUSIONS

We demonstrated injury of the CBT in patients with dysarthria following cerebral infarct in the corona radiata using DTT. This result indicates the importance of CBT evaluation for dysarthria in patients with cerebral infarct. Therefore, we suggest that evaluations of the CBT using DTT would be useful for patients with dysarthria following cerebral infarct.