Andrew A. McCall

Drug delivery for treatment of inner ear disease: current state of knowledge.

Delivery of medications to the inner ear has been an area of considerable growth in both the research and clinical realms during the past several decades. Systemic delivery of medication destined for treatment of the inner ear is the foundation on which newer delivery techniques have been developed. Because of systemic side effects, investigators and clinicians have begun developing and using techniques to deliver therapeutic agents locally. Alongside the now commonplace use of intratympanic gentamicin for Menieres disease and the emerging use of intratympanic steroids for sudden sensorineural hearing loss, novel technologies, such as hydrogels and nanoparticles, are being explored. At the horizon of inner ear drug-delivery techniques, intracochlear devices that leverage recent advances in microsystems technology are being developed to apply medications directly into the inner ear. Potential uses for such devices include neurotrophic factor and steroid delivery with cochlear implantation, RNA interference technologies, and stem-cell therapy. The historical, current, and future delivery techniques and uses of drug delivery for treatment of inner ear disease serve as the basis for this review.

Compensation Following Bilateral Vestibular Damage

Bilateral loss of vestibular inputs affects far fewer patients than unilateral inner ear damage, and thus has been understudied. In both animal subjects and human patients, bilateral vestibular hypofunction (BVH) produces a variety of clinical problems, including impaired balance control, inability to maintain stable blood pressure during postural changes, difficulty in visual targeting of images, and disturbances in spatial memory and navigational performance. Experiments in animals have shown that non-labyrinthine inputs to the vestibular nuclei are rapidly amplified following the onset of BVH, which may explain the recovery of postural stability and orthostatic tolerance that occurs within 10 days. However, the loss of the vestibulo-ocular reflex and degraded spatial cognition appear to be permanent in animals with BVH. Current concepts of the compensatory mechanisms in humans with BVH are largely inferential, as there is a lack of data from patients early in the disease process. Translation of animal studies of compensation for BVH into therapeutic strategies and subsequent application in the clinic is the most likely route to improve treatment. In addition to physical therapy, two types of prosthetic devices have been proposed to treat individuals with bilateral loss of vestibular inputs: those that provide tactile stimulation to indicate body position in space, and those that deliver electrical stimuli to branches of the vestibular nerve in accordance with head movements. The relative efficacy of these two treatment paradigms, and whether they can be combined to facilitate recovery, is yet to be ascertained.

Integration of vestibular and emetic gastrointestinal signals that produce nausea and vomiting: potential contributions to motion sickness

Abstract Vomiting and nausea can be elicited by a variety of stimuli, although there is considerable evidence that the same brainstem areas mediate these responses despite the triggering mechanism. A variety of experimental approaches showed that nucleus tractus solitarius, the dorsolateral reticular formation of the caudal medulla (lateral tegmental field), and the parabrachial nucleus play key roles in integrating signals that trigger nausea and vomiting. These brainstem areas presumably coordinate the contractions of the diaphragm and abdominal muscles that result in vomiting. However, it is unclear whether these regions also mediate the autonomic responses that precede and accompany vomiting, including alterations in gastrointestinal activity, sweating, and changes in blood flow to the skin. Recent studies showed that delivery of an emetic compound to the gastrointestinal system affects the processing of vestibular inputs in the lateral tegmental field and parabrachial nucleus, potentially altering susceptibility for vestibular-elicited vomiting. Findings from these studies suggested that multiple emetic inputs converge on the same brainstem neurons, such that delivery of one emetic stimulus affects the processing of another emetic signal. Despite the advances in understanding the neurobiology of nausea and vomiting, much is left to be learned. Additional neurophysiologic studies, particularly those conducted in conscious animals, will be crucial to discern the integrative processes in the brain stem that result in emesis.

Superior canal dehiscence syndrome associated with the superior petrosal sinus in pediatric and adult patients.

Objective: To determine whether pediatric and adult patients with superior canal dehiscence (SCD) at the superior petrosal sinus (SPS) develop superior canal dehiscence syndrome (SCDS). Study Design: Retrospective review. Setting: Tertiary care academic medical center. Patients: Pediatric and adult patients with SPS-associated SCD were identified from a database of 131 patients with SCD based on high-resolution temporal bone computed tomography. Intervention: One pediatric patient experienced incapacitating exercise-induced vertigo, and this patients superior semicircular canal defect was plugged via a transmastoid approach. The 11 remaining patients were managed by observation. Main Outcome Measure: Clinical symptoms and signs, audiologic testing, vestibular evoked myogenic potentials, and radiologic data. Results: Twelve patients, aged 15 to 84 years, with SCD caused by the SPS contacting the superior semicircular canal were identified. The most characteristic clinical feature in this population (5/12) was dizziness related to exercise and exertion. Bilateral SCD was observed in 3 patients. Eleven patients did not have severe symptoms and were managed conservatively. One patient, aged 15, required surgical intervention for incapacitating vertigo and experienced relief of symptoms with reversal of diagnostic indicators postoperatively. This is the first reported surgical repair of SCDS in a pediatric patient. Conclusion: This is the first series of patients who have SCDS due to contact of the SPS with the superior semicircular canal. Exercise and exertion-related symptoms are common in patients who have SCD owing to this cause. Transmastoid superior canal plugging is feasible and successful in treating SCDS in the pediatric patient.

Malignant Otitis Externa: Evolving Pathogens and Implications for Diagnosis and Treatment

Objective Malignant otitis externa (MOE) is an invasive infection of the temporal bone that is classically caused by Pseudomonas aeruginosa. Increasingly, however, nonpseudomonal cases are being reported. The goal of this study was to evaluate and compare the clinical presentation and outcomes of cases of MOE caused by Pseudomonas versus non-Pseudomonas organisms. Study Design Retrospective case series with chart review. Setting Tertiary care institution. Subjects and Methods Adult patients with diagnoses of MOE between 1995 and 2012 were identified. Charts were reviewed for history, clinical presentation, laboratory data, treatment, and outcomes. Results Twenty patients diagnosed with and treated for MOE at the University of Pittsburgh Medical Center between 1995 and 2012 were identified. Nine patients (45%) had cultures that grew P aeruginosa. Three patients (15%) had cultures that grew methicillin-resistant Staphylococcus aureus (MRSA). Signs and symptoms at presentation were similar across groups. However, all of the patients with Pseudomonas had diabetes, compared with 33% of MRSA-infected patients (P = .046) and 55% of all non-Pseudomonas-infected patients (P = .04). Patients infected with MRSA were treated for an average total of 4.7 more weeks of antibiotic therapy than Pseudomonas-infected patients (P = .10). Overall, patients with non-Pseudomonas infections were treated for a total of 2.4 more weeks than Pseudomonas-infected patients (P = .25). Conclusions A high index of suspicion for nonpseudomonal organisms should be maintained in patients with signs and symptoms of MOE, especially in those without diabetes. MRSA is an increasingly implicated organism in MOE.

Superior Canal Dehiscence Length and Location Influences Clinical Presentation and Audiometric and Cervical Vestibular-Evoked Myogenic Potential Testing

Superior canal dehiscence (SCD) is caused by an absence of bony covering of the arcuate eminence or posteromedial aspect of the superior semicircular canal. However, the clinical presentation of SCD syndrome varies considerably, as some SCD patients are asymptomatic and others have auditory and/or vestibular complaints. In order to determine the basis for these observations, we examined the association between SCD length and location with: (1) auditory and vestibular signs and symptoms; (2) air conduction (AC) loss and air-bone gap (ABG) measured by pure-tone audiometric testing, and (3) cervical vestibular-evoked myogenic potential (cVEMP) thresholds. 104 patients (147 ears) underwent SCD length and location measurements using a novel method of measuring bone density along 0.2-mm radial CT sections. We found that patients with auditory symptoms have a larger dehiscence (median length: 4.5 vs. 2.7 mm) with a beginning closer to the ampulla (median location: 4.8 vs. 6.4 mm from ampulla) than patients with no auditory symptoms (only vestibular symptoms). An increase in AC threshold was found as the SCD length increased at 250 Hz (95% CI: 1.7-4.7), 500 Hz (95% CI: 0.7-3.5) and 1,000 Hz (95% CI: 0.0-2.5), and an increase in ABG as the SCD length increased at 250 Hz (95% CI: 2.0-5.3), 500 Hz (95% CI: 1.6-4.6) and 1,000 Hz (95% CI: 1.3-3.3) was also seen. Finally, a larger dehiscence was associated with lowered cVEMP thresholds at 250 Hz (95% CI: -4.4 to -0.3), 500 Hz (95% CI: -4.1 to -1.0), 750 Hz (95% CI: -4.2 to -0.7) and 1,000 Hz (95% CI: -3.6 to -0.5) and a starting location closer to the ampulla at 250 Hz (95% CI: 1.3-5.1), 750 Hz (95% CI: 0.2-3.3) and 1,000 Hz (95% CI: 0.6-3.5). These findings may help to explain the variation of signs and symptoms seen in patients with SCD syndrome.

ICP, BMI, surgical repair, and CSF diversion in patients presenting with spontaneous CSF otorrhea.

Objective To assess intracranial pressure (ICP), body mass index (BMI), surgical repair, and cerebrospinal fluid (CSF) diversion in patients presenting with spontaneous CSF otorrhea. Study Design Retrospective series review. Setting Tertiary referral center. Patients Thirty-two patients were treated surgically from 2004 to 2013 for spontaneous CSF otorrhea by the principal investigators. Patients with a history of chronic ear disease and cholesteatoma, previous mastoid surgery, head trauma, or iatrogenic injury were excluded. Average age was 56 years. Twenty-two patients (69%) were female. Intervention(s) Middle fossa repair, transmastoid repair, lumbar puncture, V-P shunt, L-P shunt, and magnetic resonance imaging. Main Outcome Measure(s) Patients underwent middle fossa or transmastoid repair of tegmen defects. Intracranial pressures were determined with lumbar puncture at time of surgical repair or shortly after surgery. CSF diversion procedures were performed in patients who were found to have elevated ICP, which was not controlled medically, presented with recurrent leak or had ICP of 25 cm or greater of H2O. Preoperative BMI was calculated. Results Thirty-two patients underwent 37 operations. Average BMI was 35.0 kg/m2 (median, 34.7; range, 18.7–53.2 kg/m2). There were 21 repairs on the left and 16 on the right. The majority underwent a middle fossa craniotomy for repair (27/32). Two patients had bilateral repairs. Three patients (8%) underwent revision surgery, of which, 2 had untreated intracranial hypertension (ICP 24.5 and 24 cm H2O). ICP measurements were available for 29 patients. The mean ICP was 23.4 cm H2O (median, 24; range, 13–36 cm H20). Twenty-two patients (69%) had ICP of 20 cm or greater of H20; of those, 13 had an ICP of 25 cm or greater of H20. Seventeen patients (53%) underwent CSF diversion procedures. Conclusion Our findings of elevated ICP and BMI in patients presenting with spontaneous CSF otorrhea are consistent with previous reports in the literature. The percentage of patients that underwent CSF diversion procedures was high at 53% and represents an aggressive stance in managing elevated ICP in a population that may be at risk for subsequent leaks.

Vestibular nucleus neurons respond to hindlimb movement in the decerebrate cat

The vestibular nuclei integrate information from vestibular and proprioceptive afferents, which presumably facilitates the maintenance of stable balance and posture. However, little is currently known about the processing of sensory signals from the limbs by vestibular nucleus neurons. This study tested the hypothesis that limb movement is encoded by vestibular nucleus neurons and described the changes in activity of these neurons elicited by limb extension and flexion. In decerebrate cats, we recorded the activity of 70 vestibular nucleus neurons whose activity was modulated by limb movements. Most of these neurons (57/70, 81.4%) encoded information about the direction of hindlimb movement, while the remaining neurons (13/70, 18.6%) encoded the presence of hindlimb movement without signaling the direction of movement. The activity of many vestibular nucleus neurons that responded to limb movement was also modulated by rotating the animals body in vertical planes, suggesting that the neurons integrated hindlimb and labyrinthine inputs. Neurons whose firing rate increased during ipsilateral ear-down roll rotations tended to be excited by hindlimb flexion, whereas neurons whose firing rate increased during contralateral ear-down tilts were excited by hindlimb extension. These observations suggest that there is a purposeful mapping of hindlimb inputs onto vestibular nucleus neurons, such that integration of hindlimb and labyrinthine inputs to the neurons is functionally relevant.

Otopathology in Osteogenesis Imperfecta

Background Osteogenesis Imperfecta (OI) is a genetic disorder of connective tissue matrix. OI is caused by mutations that affect type I collagen. The hearing loss in OI is characterized by onset in early adulthood and can be conductive, sensorineural, or mixed. Objectives To describe the temporal bone histopathology in 9 individuals with OI. Materials and Methods Four adult, 1 pediatric, and 4 infant specimens were identified. Temporal bones were removed at autopsy and studied using light microscopy. Results All adults and 1 pediatric specimen showed otosclerotic lesions. The findings included examples of clinical, histologic, and cochlear otosclerosis. The temporal bones of infants showed delayed ossification of the endochondral layer of bone and of the ossicles. There were no infant specimens with otosclerotic lesions. Conclusion Hearing loss in OI may be the result of clinical or cochlear otosclerosis. Fracture or atrophy of the ossicles may also be present in OI. A third unidentified mechanism of hearing loss may lead to cochlear degeneration. The described findings of otosclerotic lesions have implications for the observed heterogeneity of hearing loss patterns and for the surgical management of hearing loss in OI.

Descending Influences on Vestibulospinal and Vestibulosympathetic Reflexes

This review considers the integration of vestibular and other signals by the central nervous system pathways that participate in balance control and blood pressure regulation, with an emphasis on how this integration may modify posture-related responses in accordance with behavioral context. Two pathways convey vestibular signals to limb motoneurons: the lateral vestibulospinal tract and reticulospinal projections. Both pathways receive direct inputs from the cerebral cortex and cerebellum, and also integrate vestibular, spinal, and other inputs. Decerebration in animals or strokes that interrupt corticobulbar projections in humans alter the gain of vestibulospinal reflexes and the responses of vestibular nucleus neurons to particular stimuli. This evidence shows that supratentorial regions modify the activity of the vestibular system, but the functional importance of descending influences on vestibulospinal reflexes acting on the limbs is currently unknown. It is often overlooked that the vestibulospinal and reticulospinal systems mainly terminate on spinal interneurons, and not directly on motoneurons, yet little is known about the transformation of vestibular signals that occurs in the spinal cord. Unexpected changes in body position that elicit vestibulospinal reflexes can also produce vestibulosympathetic responses that serve to maintain stable blood pressure. Vestibulosympathetic reflexes are mediated, at least in part, through a specialized group of reticulospinal neurons in the rostral ventrolateral medulla that project to sympathetic preganglionic neurons in the spinal cord. However, other pathways may also contribute to these responses, including those that dually participate in motor control and regulation of sympathetic nervous system activity. Vestibulosympathetic reflexes differ in conscious and decerebrate animals, indicating that supratentorial regions alter these responses. However, as with vestibular reflexes acting on the limbs, little is known about the physiological significance of descending control of vestibulosympathetic pathways.