Brainstem auditory-evoked potentials as an objective tool for evaluating hearing dysfunction in traumatic brain injury

Influence of High-Frequency Repetitive Transcranial Magnetic Stimulation on Neurobehavioral and Electrophysiology in Patients with Disorders of Consciousness

Objective

High-frequency repetitive transcranial magnetic stimulation (HF-rTMS) has been proposed as a promising therapeutic intervention for patients with disorders of consciousness (DOC). However, its therapeutic effects in the literature are inconsistently documented. The primary aim of this study was to explore the alterations in neural connectivity and neurobehavioral reactivity during rTMS modulation in patients with DOC. In addition, safety was investigated as a secondary aim.

Methods

The presence of bilateral N20 components in DOC patients was determined by somatosensory-evoked potential (SEP) before enrollment in the study. A total of 64 patients were enrolled and randomly placed into the active and sham groups. Ultimately, 50 patients completed the study. Twenty-five patients in the active group underwent real HF-rTMS, and 25 patients in the sham group underwent sham HF-rTMS, which was delivered over the left dorsolateral prefrontal cortex (DLPFC). The outcome measures of performed pre- and postintervention included the latencies of the N20 and N20-P25 amplitudes of SEP, brainstem auditory-evoked potential (BAEP) grade, JFK Coma Recovery Scale-Revised (CRS-R) score, and Glasgow Coma Scale (GCS) score; any adverse events were recorded at any time during the intervention.

Result

Following six weeks of treatment, a significant increase was observed in the total CRS-R and GCS scores, and the N20-P25 amplitudes of patients in the two groups were compared with that obtained from preintervention (all p values < 0.05). The waves of BAEP in the two groups also showed a trend toward normalized activity compared with preintervention grades (p values < 0.05). A significant decrease in the latencies of N20 (p values < 0.001) was observed in the active group compared with measurements obtained from preintervention, whereas no significant decrease was observed in the sham group (p values = 0.013). The improvement in total CRS-R scores (p values = 0.002), total GCS scores (p values = 0.023), and N20-P25 amplitudes (p values = 0.011) as well as the decrease in latencies of N20 (p values = 0.018) and change in BAEP grades (p values = 0.013) were significantly different between the two groups. The parameters in neural connectivity (N20-P25 amplitudes, N20 latencies, and BAEP grades) were significantly correlated with the total CRS-R and GCS scores at postintervention, and the changes of CRS-R before and after interventions have a positive relationship with N20-P25 amplitudes. No adverse events related to the rTMS protocol were recorded.

Conclusion

Neural connectivity levels are affected by HF-rTMS and are significantly related to clinical responses in DOC patients with the presence of bilateral N20. The elevation of neural connectivity levels may lay a foundation for successful HF-rTMS treatment for DOC patients.

Characteristics of a rat model of an open craniocerebral injury at simulated high altitude

To establish a rat model of an open craniocerebral injury at simulated high altitude and to examine the characteristics of this model. Rats were divided randomly into a normobaric group and a high-altitude group and their corresponding control groups. A rat model of an open craniocerebral injury was established with a nail gun shot. Simulated high-altitude conditions were established with a hypobaric chamber at 0.6 ATA to mimic pressure at an altitude of 4000 m. Mortality, brain water content (BWC), Evans blue content, pathology, regional cerebral blood flow (rCBF), partial pressure of brain tissue oxygen (PbtO₂), and brainstem auditory-evoked potential were observed after injury. The mortality of the high-altitude group was significantly greater than that of the normobaric group within 72 h after injury (P<0.05). BWC and Evans blue content increased by 48 h after injury (P<0.05); pathological changes in damaged brains were more serious. In contrast, rCBF and PbtO₂ had decreased markedly by 72 h (P<0.01); brainstem auditory-evoked potential values were significantly prolonged (P<0.05). Moreover, an inverse correlation between rCBF and BWC and a positive correlation between rCBF and PbtO₂ were found. The rat model of an open craniocerebral injury at simulated high altitude can be established successfully using a nail gun shot and a hypobaric chamber. The injury characteristics at high altitude were more serious, rapid, and prolonged than those in the normobaric group.

Relationship between severity of traumatic brain injury (TBI) and extent of auditory dysfunction

OBJECTIVE

To find out the relationship between severity of traumatic brain injury (TBI) and extent of auditory dysfunction.

BACKGROUND

Most of the studies have taken the subjects with TBI as one group without taking into account the extent of head injury viz. mild, moderate and severe. Combining all the three groups has resulted in presenting an incomplete picture of auditory deficits following TBI.

METHODS AND PROCEDURES

The sample population consisted of 290 subjects with TBI (study group) and 50 otologically normal subjects as controls. The subjects in the study group were further sub-divided into mild (n = 150), moderate (n = 100) and severe (n = 40) TBI. The audiological assessment consisted of pure tone audiometry, speech audiometry, tympanometry, acoustic reflex testing, auditory brainstem response and middle latency response audiometry.

RESULTS AND CONCLUSIONS

An association was observed between the extent of auditory dysfunction and severity of TBI. This association was more pronounced for hearing status at high frequencies and ABR/MLR components. ABR Wave V absolute latency and I-V interpeak latency increased with severity of TBI. Amplitude of MLR wave Na and Pa decreased with increasing severity. It is suggested that subjects should be evaluated for hearing difficulties based on their severity of TBI.

Audiological deficits after closed head injury

BACKGROUND

Damage to the peripheral auditory structures has long been recognized as a common component of head injury. It is estimated that a majority of patients with skull trauma have resultant hearing impairment. Damage to the peripheral and/or central auditory pathways can occur as a primary or secondary injury. Considering the high incidence of hearing loss, it was considered worthwhile to conduct an in-depth investigation by administering a comprehensive audiological test battery on head-injured patients.

METHOD

The sample population consisted of 290 subjects with closed head injury (study group) and 50 subjects with otologically normal subjects (control group). The subjects in the study group were further divided into mild (n = 150), moderate (n = 100), and severe (n = 40) category on the basis of Glasgow Coma Scale score. The audiological assessment consisted of pure tone audiometry, speech audiometry, tympanometry, acoustic reflex testing, auditory brain stem response audiometry, and middle latency response audiometry.

RESULTS AND CONCLUSIONS

It is concluded that there is higher prevalence of hearing impairment in the study group compared with control group. Majority of the patients who incur hearing loss after closed head injury have mild degree of hearing impairment. A significant difference between the study and control group observed on majority of the auditory brain stem response and middle latency response parameters studied.

Repetitive transcranial magnetic stimulation-associated neurobehavioral gains during coma recovery

BACKGROUND

Repetitive transcranial magnetic stimulation (rTMS) is a noninvasive method to induce changes in cortical neural excitability. This report presents findings from the first participant of a safety and efficacy study that examined a therapeutic rTMS protocol for persons with severe traumatic brain injury (TBI).

OBJECTIVE

The primary hypothesis was that there will be no adverse events related to the provision of a 6-week rTMS protocol for persons with severe TBI who remain, at best, in a minimally conscious state for longer than 3 months. The secondary hypothesis was that the rTMS protocol would induce significant neurobehavioral gains during treatment and that these gains would persist at 6-week follow-up.

METHODS

A 6-week rTMS protocol (30 sessions) was delivered to a 26-year-old man who remained in a vegetative state 287 days after severe TBI. Stimulation was directed over the right dorsolateral prefrontal cortex. Repeated safety measures, neurobehavioral assessments, clinical examinations, and evoked potentials (EP) were obtained at baseline, every fifth rTMS session (weekly), and at a 6-week follow-up.

RESULTS

There were no adverse events related to the provision of rTMS treatment. A trend toward significant (P = .066) neurobehavioral gains was temporally related to provision of rTMS. Left-sided brain stem auditory EP wave V latencies and waves I to V interpeak latencies improved along with neurobehavioral gains during provision of rTMS, suggesting that improved neural conduction in the pathway mediated the neurobehavioral improvements.

CONCLUSIONS

Repetitive TMS merits further investigation as a safe therapeutic intervention to alter neural activity, to modulate neural activity, and/or to facilitate recovery in persons with disordered consciousness subsequent to severe TBI.