Beyond CPAP: modifying upper airway output for the treatment of OSA

Obstructive Sleep Apnea (OSA) is exceedingly common but often under-treated. Continuous positive airway pressure (CPAP) has long been considered the gold standard of OSA therapy. Limitations to CPAP therapy include adherence and availability. The 2021 global CPAP shortage highlighted the need to tailor patient treatments beyond CPAP alone. Common CPAP alternative approaches include positional therapy, mandibular advancement devices, and upper airway surgery. Upper airway training consists of a variety of therapies, including exercise regimens, external neuromuscular electrical stimulation, and woodwind instruments. More invasive approaches include hypoglossal nerve stimulation devices. This review will focus on the approaches for modifying upper airway muscle behavior as a therapeutic modality in OSA.

Leave No Stone Unturned: A Case of an Actinomyces Rhinolith Presenting With Chronic Cough and Throat Pain

Actinomycosis infection in the nasal cavity, especially an actinomyces rhinolith, is extremely rare. It should be considered in cases where a heterogenous calcified mass is found within the nasal cavity on endoscopy and radiographically. Treatment includes surgical debridement and a prolonged course of antibiotics, unique from the more typically encountered fungus ball. This case highlights the broad differential for chronic cough and throat pain and the importance of considering sinonasal contributions to throat symptoms.

Voice Outcomes From Direct Vocal Fold Testosterone Injections, a Case Report

Here we provide the first demonstration of targeted vocal fold testosterone injection to achieve voice masculinization in 2 transgender male patients. Successful voice outcome was achieved in 2-3 weeks, without side effects, and continues to be durable. Laryngoscope, 2023.

The Feasibility of Outpatient Type I Thyroplasty with Laryngeal Reinnervation

Type I thyroplasty has increasingly been performed on an outpatient basis. Laryngeal reinnervation is recognized for its long-term and functional benefits but is typically performed inpatient under general anesthesia. Herein we report the first published outpatient type I thyroplasty with laryngeal reinnervation performed under monitored anesthesia care (MAC). Three adults underwent type I thyroplasty with ansa cervicalis to recurrent laryngeal nerve (RLN) reinnervation. A 23-year-old female with a history of generalized idiopathic epilepsy s/p vagal nerve stimulator implantation presented with persistent dysphonia. She developed longstanding left vocal fold paralysis. She underwent left type I thyroplasty with silastic implant and ansa cervicalis to RLN neurorrhaphy under MAC-local anesthesia. The patient was discharged home on the day of surgery. Two additional patients underwent the same procedure, including a 58-year-old male with postsurgical dysphonia who was admitted for overnight observation due to a small amount of incisional crepitus and a 23-year-old female with postsurgical vocal cord paralysis who was admitted overnight due to multiple comorbidities. Both were discharged on post-operative day one without issue and demonstrated improvement in voice at follow up. Outpatient type I thyroplasty with laryngeal reinnervation under MAC is feasible with proper patient selection.

Upper Esophageal Sphincter Compression Device as an Adjunct to Proton Pump Inhibition for Laryngopharyngeal Reflux

BACKGROUND

The Reflux Band, an external upper esophageal sphincter (UES) compression device, reduces esophago-pharyngeal reflux events. This study aimed to assess device efficacy as an adjunct to proton pump inhibitor (PPI) therapy in patients with laryngopharyngeal reflux (LPR).

METHODS

This two-phase prospective clinical trial enrolled adults with at least 8 weeks of laryngeal symptoms (sore throat, throat clearing, dysphonia) not using PPI therapy at two tertiary care centers over 26 months. Participants used double dose PPI for 4 weeks in Phase 1 and the external UES compression device nightly along with PPI for 4 weeks in Phase 2. Questionnaire scores and salivary pepsin concentration were measured throughout the study. The primary endpoint of symptom response was defined as reflux symptom index (RSI) score ≤ 13 and/or > 50% reduction in RSI.

RESULTS

Thirty-one participants completed the study: 52% male, mean age 47.9 years (SD 14.0), and mean body mass index (BMI) 26.2 kg/m² (5.1). Primary endpoint was met in 11 (35%) participants after Phase 1 (PPI alone) and 17 (55%) after Phase 2 (Device + PPI). Compared to baseline, mean RSI score (24.1 (10.9)) decreased at end of Phase 1 (PPI alone) (21.9 (9.7); p = 0.06) and significantly decreased at end of Phase 2 (Device + PPI) (15.5 (10.3); p < 0.01). Compared to non-responders, responders to Device + PPI had a significantly lower BMI (p = 0.02) and higher salivary pepsin concentration (p = 0.01).

CONCLUSION

This clinical trial highlights the potential efficacy of the external UES compression device (Reflux Band) as an adjunct to PPI for patients with LPR (ClinicalTrials.Gov NCT03619811).

Breathy Dysphonia, Not Just a Pain in the Neck

We describe a rare occurrence of unilateral vocal fold paralysis associated with a cervical osteophyte abutting the course of the recurrent laryngeal nerve. Trans-nasal laryngoscopy is vital in diagnosing vocal fold paralysis, but often does not provide insight into etiology. This case highlights the importance of radiographic imaging in newly diagnosed vocal fold paralysis, and underscores the principle that a diagnosis is not idiopathic until all sources have been ruled out.

Dynamics of Intrinsic Laryngeal Muscle Contraction

OBJECTIVES

Laryngeal function requires neuromuscular activation of the intrinsic laryngeal muscles (ILMs). Rapid activation of the ILMs occurs in cough, laughter, and voice-unvoiced-voiced segments in speech and singing. Abnormal activation is observed in hyperfunctional disorders such as vocal tremor and dystonia. In this study, we evaluate the dynamics of ILM contraction.

STUDY/DESIGN

Basic science study in an in vivo canine model.

METHODS

The following ILMs were stimulated: thyroarytenoid (TA), lateral cricoarytenoid/interarytenoid (LCA/IA), cricothyroid (CT), all laryngeal adductors (LCA/IA/TA), and the posterior cricoarytenoid (PCA). Neuromuscular stimulation was performed via the respective nerves at current levels needed to achieve maximum vocal fold posture change. Muscle contraction and posture changes were recorded with high speed video (HSV). HSV frames were then analyzed to measure response times required from the onset of muscle contraction to the time the vocal folds achieved maximum posture change.

RESULTS

In all muscles, the onset of posture change occurred within 10 to 12 milliseconds after neuromuscular stimulation. The average times ( ± standard deviation) to achieve final posture were as follows: TA 34.5 ± 6 ms (N = 15), LCA/IA 55 ± 12 ms (N = 14), recurrent laryngeal nerve 43 ± 8 ms (N = 18), CT 100.8 ± 17 ms (N = 26), and PCA 91.2 ± 8 ms (N = 3). Data distribution appeared normal.

CONCLUSION

Results showed a difference in muscle activation time between different ILMs consistent with reported differences in muscle fiber composition. These data also provide an estimate of the limits of laryngeal contraction frequency in physiologic and pathologic laryngeal states.

LEVEL OF EVIDENCE

NA Laryngoscope, 129:E21-E25, 2019.

Transplanted human multipotent stromal cells reduce acute tongue fibrosis in rats

Background

Tongue fibrosis resulting from head and neck cancer, surgery, radiation, chemotherapy, or a combination thereof devastates one's quality of life. Therapeutic options are limited. Here we investigate human bone marrow-derived multipotent stromal cells (MSC) as a novel injectable treatment for post-injury tongue fibrosis.

Methods

MSCs were grown in culture. Eighteen athymic rats underwent unilateral partial glossectomy. After two weeks for scar formation, a single injection was performed in the tongue scar. Three treatment groups were studied: low and high concentration MSC, and control media injection. Tongues were harvested for evaluation at three weeks post-treatment.

Results

Dense fibrosis was achieved in control animals at five weeks. High concentration MSC reduced cross sectional scar burden (P = .007) and pathologic score for inflammation and fibrosis.

Conclusion

This study establishes the feasibility of a novel rodent tongue fibrosis model, and begins to assess the utility of human MSCs to reduce scar burden.

Level of Evidence

N/a.

Sentinel lymph node biopsy in cutaneous melanoma of the head and neck using the indocyanine green SPY Elite system

PURPOSE

Lymph node status is the single most important prognostic factor for patients with early-stage cutaneous melanoma. Sentinel lymph node biopsy (SLNB) has become the standard of care for intermediate depth melanomas. Modern SLNB implementation includes technetium-99 lymphoscintigraphy combined with local administration of a vital blue dye. However, sentinel lymph nodes may fail to localize in some cases and false-negative rates range from 0 to 34%. Here we demonstrate the feasibility of a new sentinel lymph node biopsy technique using indocyanine green (ICG) and the SPY Elite near-infrared imaging system.

MATERIALS AND METHODS

Cases of primary cutaneous melanoma of the head and neck without locoregional metastasis, underwent SLNB at a single quaternary care institution between May 2016 and June 2017. Intraoperatively, 0.25 mL of ICG was injected intradermal in 4 quadrants around the primary lesion. 10-15 minute circulation time was permitted. SPY Elite identified the sentinel lymph node within the nodal basin marked by lymphoscintigraphy. Target first echelon lymph nodes were confirmed with a gamma probe and ICG fluorescence.

RESULTS

14 patients were included with T1a to T4b cutaneous melanomas. Success rates for sentinel lymph node identification using lymphoscintigraphy and the SPY Elite system were both 86%. Zero false negatives occurred. Median length of follow-up was 323 days.

CONCLUSIONS

In this pilot study, Indocyanine green near-infrared fluorescence demonstrates a safe, and facile method of sentinel lymph node biopsy for cutaneous melanoma of the head and neck compared with lymphoscintigraphy and vital blue dyes.

Hirano's cover-body model and its unique laryngeal postures revisited

OBJECTIVES/HYPOTHESIS

In 1974, Minoru Hirano proposed his theory of voice production that is now known as the cover-body theory. He described the thyroarytenoid (TA) and cricothyroid (CT) muscles as the major determinants of vocal fold shape and stiffness, and theorized four typical laryngeal configurations resulting from unique TA/CT activations, with implications for the resulting voice quality. In this study, we directly observed the vocal fold medial surface shape under Hirano's unique TA/CT activation conditions to obtain a three-dimensional (3D) understanding of these laryngeal configurations during muscle activation.

STUDY DESIGN

In vivo canine hemilarynx model.

METHODS

Flesh points were marked along the medial surface of the vocal fold. Selective TA and CT activation were performed via respective laryngeal nerves. 3D reconstructions of the vocal fold medial surface were derived using digital image correlation.

RESULTS

Low level TA and CT activation yielded anteroposterior lengthening and vertical thinning of the vocal fold. When TA activation is far greater than CT, the vocal fold shortens and thickens. With slightly greater TA than CT, activation the vocal length is maintained on average, whereas its vertical thickness decreases. With CT far greater than TA activation, the vocal fold lengthens and thins. In all conditions, glottal contour changes remained minimal.

CONCLUSIONS

Analysis of the 3D geometry of the vocal fold medial surface under Hirano's four typical laryngeal configurations revealed that the key geometric changes during TA/CT interactions lie within the anteroposterior length and the vertical thickness of the vocal fold.

LEVEL OF EVIDENCE

NA. Laryngoscope, 128:1412-1418, 2018.

Predictors of prolongation in radiation treatment time in a veteran population treated with chemoradiation for oropharyngeal cancer

BACKGROUND

Prolonged radiation treatment time (RTT) is associated with worse tumor control. Here we identify and determine the implications of factors that predict treatment prolongation in Veterans Affairs (VA) patients undergoing chemoradiation.

METHODS

Chart review from July 2000 to October 2013. 81 patients with advanced stage oropharyngeal cancer treated with chemoradiation.

RESULTS

Twenty-nine patients (35.8%) had RTT prolonged by ≥10 days. Prolongation mainly resulted from acute treatment toxicity (n = 22, 76%). There was no significant difference in RTT for patients treated with concurrent cisplatin versus cetuximab, or in patients treated with or without induction chemotherapy. One-/three-year locoregional control and overall survival rates of 83.4%/76.3% and 83.5%/63.6% for patients without prolonged RTT versus 61.8%/61.8% and 82.8%/73.8% for those with prolongation (p >.05).

CONCLUSIONS

Prolonged RTT is a significant predictor of worse locoregional control and predominantly resulted from treatment side effects. More aggressive regimens with induction and concurrent chemotherapy did not predispose to prolonged RTT.

Israel rake retractor modification to improve exposure during oropharyngeal surgery on patients with larger body habitus

PURPOSE

Elective oropharyngeal surgery including tonsillectomy and uvulopalatopharyngoplasty performed for obstructive sleep apnea is increasingly performed on patients of larger body habitus. The use of the Crowe-Davis retractor in such patients may be complicated by a large barrel-chest making it difficult to anchor the retractor to the Mayo stand for suspension limiting oropharyngeal exposure. Here, we present a simple modification using the Israel Retractor to facilitate suspension of the Crowe-Davis mouth gag.

METHODS

Operational instructions were followed for Israel retractor modification in oropharyngeal surgery.

RESULTS

The Crowe-Davis retractor is able to anchor to the Israel retractor, whose prongs articulate on the Mayo Stand for suspension. This extension allows suspension of patients with larger body habitus in oropharyngeal surgery.

CONCLUSIONS

Use of the Israel retractor as an extension of the Crowe-Davis retractor handle provides an easy, quick, safe, and reliable method for placing patients of larger body habitus into suspension.

Quantitative Evaluation of the In Vivo Vocal Fold Medial Surface Shape

OBJECTIVES/HYPOTHESIS

Glottal insufficiency is a common clinical problem in otolaryngology and medialization laryngoplasty (ML) procedures remain the primary treatment modality. Although the goal of ML is to restore physiologic glottal posture and achieve optimal phonation, this posture has not been directly measured. In this study, we assessed glottal medial surface contour changes with selective activation of the intrinsic laryngeal muscles (ILMs).

STUDY DESIGN

Basic science study using an in vivo canine hemilarynx model.

METHODS

In an in vivo canine hemilarynx, India ink was used to mark fleshpoints in a grid-like fashion along the medial surface of the vocal fold and ILMs were activated in a graded manner. A right-angled prism provided two views of the medial surface, which were recorded using a high-speed camera and used to reconstruct the 3D posture deformations of the medial surface.

RESULTS

Thyroarytenoid (TA) muscle activation results in initial inferomedial bulging and increased glottal channel thickness and then glottal adduction with a final rectangular glottal channel shape. Lateral cricoarytenoid (LCA) activation closes the posterior glottis but final posture remains slightly convergent. Together, TA + LCA forms a rectangular glottis with an increased glottal vertical thickness. Posterior cricoarytenoid activation results in abduction and a slightly divergent glottis, whereas cricothyroid activation elongates the glottis and reduces the glottal channel vertical thickness.

CONCLUSIONS

A quantitative analysis of in vivo canine vocal fold medial surface upon activation of selective ILMs is provided. This may guide our therapeutic efforts during medialization laryngoplasty, as well as computational modeling of laryngeal physiology.

More than just tissue diagnosis in a patient with maxillofacial bony lesions and hypercalcemia

Brown tumors are a definitive feature of hyperparathyroidism. They are well-demarcated osteolytic lesions commonly in the appendicular skeleton. Primary hyperparathyroidism is typically suggested by hypercalcemia and hypophosphatemia on routine labs. Much more rarely do these cases present with a craniofacial mass. Here we investigate a unique presentation of terminal stage primary hyperparathyroidism with a growing maxillary mass emphasizing the importance of a broad differential diagnosis and key diagnostic studies. Hyperparathyroidism can present in very unique ways. As otolaryngologists in the frontline, we must think beyond just tissue diagnoses so that appropriate and expedited care may be implemented. Laryngoscope, 127:1318-1321, 2017.

Three-dimensional posture changes of the vocal fold from paired intrinsic laryngeal muscles

OBJECTIVES/HYPOTHESIS

Although the geometry of the vocal fold medial surface affects voice quality and is critical in the treatment of glottic insufficiency, the prephonatory shape of the vocal fold medial surface is not well understood. In this study, we activated intrinsic laryngeal muscles individually and in combinations, and recorded the temporal sequence and precise three-dimensional configurational changes of the vocal fold medial surface.

STUDY DESIGN

In vivo canine hemilarynx model.

METHODS

A hemilaryngectomy was performed in an in vivo canine model and ink was used to mark the medial surface of the in situ vocal fold in a grid-like fashion. The thyroarytenoid (TA), lateral cricoarytenoid (LCA), cricothyroid (CT), and posterior cricoarytenoid (PCA) muscles were stimulated individually and in combinations. A right-angle prism whose hypotenuse formed the glottal midline provided two distinct views of the medial surface for a high-speed digital camera. Image-processing package DaVis (LaVision Inc., Goettingen, Germany) allowed time series cross-correlation analysis for three-dimensional deformation calculations of the vocal fold medial surface.

RESULTS

Combined TA and LCA activation yields an evenly adducted rectangular glottal surface. Addition of thyroarytenoid to cricoarytenoid adducts the vocal fold from inferior to superior in a graded fashion allowing formation of a divergent glottis. Posterior cricoarytenoid has a bimodal relationship with thyroarytenoid favoring abduction. Cricothyroid and lateral cricoarytenoid yield unique glottal postures necessary but likely not conducive for efficient phonation.

CONCLUSIONS

Understanding the three-dimensional geometry of the vocal fold medial surface will help us better understand the cause-effect relationship between laryngeal physiology and phonation.

LEVEL OF EVIDENCE

NA Laryngoscope, 127:656-664, 2017.

Hypopharyngeal venous malformation presenting with foreign body sensation and dysphagia

OBJECTIVE

Review the importance of imaging selection and clinicoanatomic correlation for a vascular malformations presenting with unique symptomatology.

METHODS

Case study and literature review.

RESULTS

A 64-year-old female presented with globus and dysphagia ongoing for 40 years. Esophagogastroduodenoscopy discovered a hypopharyngeal mass. A CT scan showed a soft tissue mass with shotty calcifications. Flexible laryngoscopy revealed a bluish compressible mass. MRI showed T2 hyperintensity with heterogeneous enhancement resulting in the diagnosis of a low-flow vascular malformation.

CONCLUSIONS

All globus is not equal. Attention to symptoms, anatomy, and imaging selection is crucial for the diagnosis and treatment of vascular malformations uniquely presenting with dysphagia.

Suppression of motor cortical excitability in anesthetized rats by low frequency repetitive transcranial magnetic stimulation

Repetitive transcranial magnetic stimulation (rTMS) is a widely-used method for modulating cortical excitability in humans, by mechanisms thought to involve use-dependent synaptic plasticity. For example, when low frequency rTMS (LF rTMS) is applied over the motor cortex, in humans, it predictably leads to a suppression of the motor evoked potential (MEP), presumably reflecting long-term depression (LTD) -like mechanisms. Yet how closely such rTMS effects actually match LTD is unknown. We therefore sought to (1) reproduce cortico-spinal depression by LF rTMS in rats, (2) establish a reliable animal model for rTMS effects that may enable mechanistic studies, and (3) test whether LTD-like properties are evident in the rat LF rTMS setup. Lateralized MEPs were obtained from anesthetized Long-Evans rats. To test frequency-dependence of LF rTMS, rats underwent rTMS at one of three frequencies, 0.25, 0.5, or 1 Hz. We next tested the dependence of rTMS effects on N-methyl-D-aspartate glutamate receptor (NMDAR), by application of two NMDAR antagonists. We find that 1 Hz rTMS preferentially depresses unilateral MEP in rats, and that this LTD-like effect is blocked by NMDAR antagonists. These are the first electrophysiological data showing depression of cortical excitability following LF rTMS in rats, and the first to demonstrate dependence of this form of cortical plasticity on the NMDAR. We also note that our report is the first to show that the capacity for LTD-type cortical suppression by rTMS is present under barbiturate anesthesia, suggesting that future neuromodulatory rTMS applications under anesthesia may be considered.

Translational neuromodulation: approximating human transcranial magnetic stimulation protocols in rats

OBJECTIVE

Transcranial magnetic stimulation (TMS) is a well-established clinical protocol with numerous potential therapeutic and diagnostic applications. Yet, much work remains in the elucidation of TMS mechanisms, optimization of protocols, and in development of novel therapeutic applications. As with many technologies, the key to these issues lies in the proper experimentation and translation of TMS methods to animal models, among which rat models have proven popular. A significant increase in the number of rat TMS publications has necessitated analysis of their relevance to human work. We therefore review the essential principles for the approximation of human TMS protocols in rats as well as specific methods that addressed these issues in published studies.

MATERIALS AND METHODS

We performed an English language literature search combined with our own experience and data. We address issues that we see as important in the translation of human TMS methods to rat models and provide a summary of key accomplishments in these areas.

RESULTS

  An extensive literature review illustrated the growth of rodent TMS studies in recent years. Current advances in the translation of single, paired-pulse, and repetitive stimulation paradigms to rodent models are presented. The importance of TMS in the generation of data for preclinical trials is also highlighted.

CONCLUSIONS

Rat TMS has several limitations when considering parallels between animal and human stimulation. However, it has proven to be a useful tool in the field of translational brain stimulation and will likely continue to aid in the design and implementation of stimulation protocols for therapeutic and diagnostic applications.

Can noninvasive brain stimulation enhance cognition in neuropsychiatric disorders?

Cognitive impairment is a core symptom of many neuropsychiatric diseases and a key contributor to the patient's quality of life. However, an effective therapeutic strategy has yet to be developed. Noninvasive brain stimulation techniques, namely transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS), are promising techniques that are under investigation for a variety of otherwise treatment-resistant neuropsychiatric diseases. Notably, these tools can induce alterations in neural networks subserving cognitive operations and thus may provide a means for cognitive restoration. The purpose of this article is to review the available evidence concerning cognitive enhancing properties of noninvasive brain stimulation in neuropsychiatry. We specifically focus on major depression, Alzheimer's disease, schizophrenia, autism and attention deficit hyperactivity disorder (ADHD), where cognitive dysfunction is a major symptom and some studies have been completed with promising results. We provide a critical assessment of the available research and suggestions to guide future efforts. This article is part of a Special Issue entitled 'Cognitive Enhancers'.

Characterizing brain cortical plasticity and network dynamics across the age-span in health and disease with TMS-EEG and TMS-fMRI

Brain plasticity can be conceptualized as nature's invention to overcome limitations of the genome and adapt to a rapidly changing environment. As such, plasticity is an intrinsic property of the brain across the lifespan. However, mechanisms of plasticity may vary with age. The combination of transcranial magnetic stimulation (TMS) with electroencephalography (EEG) or functional magnetic resonance imaging (fMRI) enables clinicians and researchers to directly study local and network cortical plasticity, in humans in vivo, and characterize their changes across the age-span. Parallel, translational studies in animals can provide mechanistic insights. Here, we argue that, for each individual, the efficiency of neuronal plasticity declines throughout the age-span and may do so more or less prominently depending on variable 'starting-points' and different 'slopes of change' defined by genetic, biological, and environmental factors. Furthermore, aberrant, excessive, insufficient, or mistimed plasticity may represent the proximal pathogenic cause of neurodevelopmental and neurodegenerative disorders such as autism spectrum disorders or Alzheimer's disease.

Measures of cortical inhibition by paired-pulse transcranial magnetic stimulation in anesthetized rats

Paired-pulse transcranial magnetic stimulation (ppTMS) is a noninvasive method to measure cortical inhibition in vivo. Long interpulse interval (50-500 ms) ppTMS (LI-ppTMS) provokes intracortical inhibitory circuits and can reveal pathologically impaired cortical inhibition in disorders such as epilepsy. Adaptation of ppTMS protocols to rodent disease models is highly desirable to facilitate basic and translational research. We previously adapted single-pulse TMS (spTMS) methods to rats, but ppTMS has yet to be applied. Specifically, whether ppTMS elicits an inhibitory response in rodents is unknown. ppTMS in rats also requires anesthesia, a setting under which the preservation of these measures is undetermined. We therefore tested, in anesthetized rats, whether anesthetic choice affects spTMS-motor-evoked potentials (MEPs), LI-ppTMS in rats, as in humans, elicits intracortical inhibition of the MEP, and rat LI-ppTMS inhibition is acutely impaired in a seizure model. Rats were anesthetized with pentobarbital (PB) or ketamine-atropine-xylazine (KAX) and stimulated unilaterally over the motor cortex while recording bilateral brachioradialis MEPs. LI-ppTMS was applied analogous to human long interval intracortical inhibition (LICI) protocols, and acute changes in inhibition were evaluated following injection of the convulsant pentylenetetrazole (PTZ). We find that spTMS-evoked MEPs were reliably present under either anesthetic, and that LI-ppTMS elicits inhibition of the conditioned MEP in rats, similar to human LICI, by as much as 58 ± 12 and 71 ± 11% under PB and KAX anesthesia, respectively. LI-ppTMS inhibition was reduced to as much as 53% of saline controls following PTZ injection, while spTMS-derived measures of corticospinal excitability were unchanged. Our data show that regional inhibition, similar to human LICI, is present in rats, can be elicited under PB or KAX anesthesia, and is reduced following convulsant administration. These results suggest a potential for LI-ppTMS as a biomarker of impaired cortical inhibition in murine disease models.

Lateralization of forelimb motor evoked potentials by transcranial magnetic stimulation in rats

OBJECTIVES

To approximate methods for human transcranial magnetic stimulation (TMS) in rats, we tested whether lateralized cortical stimulation resulting in selective activation of one forelimb contralateral to the site of stimulation could be achieved by TMS in the rat.

METHODS

Motor evoked potentials (MEP) were recorded from the brachioradialis muscle bilaterally in adult male anesthetized rats (n=13). A figure-of-eight TMS coil was positioned lateral to midline. TMS intensity was increased stepwise from subthreshold intensities to maximal machine output in order to generate input-output curves and to determine the motor threshold (MT) for brachioradialis activation.

RESULTS

In 100% of the animals, selective activation of the contralateral brachioradialis, in the absence of ipsilateral brachioradialis activation was achieved, and the ipsilateral brachioradialis was activated only at TMS intensities exceeding contralateral forelimb MT. With increasing TMS intensity, the amplitudes of both the ipsilateral and contralateral signals increased in proportion to TMS strength. However, the input-output curves for the contralateral and ipsilateral brachioradialis were significantly different (p<0.001) such that amplitude of the ipsilateral MEP was reliably lower than the contralateral signal.

CONCLUSIONS

We demonstrate that lateralized TMS leading to asymmetric brachioradialis activation is feasible with conventional TMS equipment in anesthetized rats.

SIGNIFICANCE

These data show that TMS can be used to assess the unilateral excitability of the forelimb descending motor pathway in the rat, and suggest that rat TMS protocols analogous to human TMS may be applied in future translational research.