Gentamicin delivery to the inner ear: Does endolymphatic hydrops matter?

Low-Dose Intratympanic Gentamicin for Unilateral Ménière‘s Disease: Accuracy of Early Vestibulo-Ocular Reflex Gain Reduction in Predicting Long-Term Clinical Outcome

Background

The number of intratympanic gentamicin (ITG) injections needed to achieve vertigo control in patients with intractable Ménière's disease (MD) may vary from a single dose to several instillations. Changes in different vestibular test results have been used to define an endpoint of treatment, including the decrease of the vestibulo-ocular reflex (VOR) gain elicited by the head-impulse test.

Objective

To assess the accuracy of the VOR gain reduction after horizontal canal stimulation, as measured with the video head-impulse test (vHIT) 1 month after the first intratympanic injection, in predicting the need for one or more instillations to control vertigo spells in the long term.

Methods

The VOR gain reduction was calculated in 47 patients submitted to (ITG) therapy 1 month after the first instillation.

Results

Single intratympanic treatment with gentamicin has a 59.6% efficacy in vertigo control in the long term. Hearing change in the immediate period after treatment (1 month) is not significant to pre-treatment result and is similar for patients who needed multiple doses due to recurrence. Chronic disequilibrium and the need for vestibular rehabilitation were less frequent in patients with a good control of vertigo with just one single injection of gentamicin. A fair accuracy was obtained for the VOR gain reduction of the horizontal canal (area under the curve = 0.729 in the Receiver Operating Characteristic analysis) in predicting the need for one or more ITG.

Conclusions

Single intratympanic treatment with gentamicin is an effective treatment for patients with MD. That modality of treatment has very limited damaging effect in hearing. The degree of vestibular deficit induced by the treatment is significant as measured by the reduction in the gain of the VOR but not useful for prognostic purposes.

Contralateral spreading of substances following intratympanic nanoparticle-conjugated gentamicin injection in a rat model

This study was performed to investigate the Eustachian tube as a potential route for contralateral spreading following intratympanic nanoparticle (NP)-conjugated gentamicin injection in a rat model. Sprague–Dawley rats were divided into three groups and substances were injected in the right ear: group 1 (fluorescent magnetic nanoparticles [F-MNPs], n = 4), group 2 (F-MNP-conjugated gentamicin [F-MNP@GM], n = 2), and control group (no injections, n = 2). T2-weighted sequences corresponding to the regions of interest at 1, 2, and 3 h after intratympanic injection were evaluated, along with immunostaining fluorescence of both side cochlea. The heterogeneous signal intensity of F-MNPs and F-MNP@GM on T2-weighted images, observed in the ipsilateral tympanum, was also detected in the contralateral tympanum in 4 out of 6 rats, recapitulating fluorescent nanoparticles in the contralateral cochlear hair cells. Computational simulations demonstrate the contralateral spreading of particles by gravity force following intratympanic injection in a rat model. The diffusion rate of the contralateral spreading relies on the sizes and surface charges of particles. Collectively, the Eustachian tube could be a route for contralateral spreading following intratympanic injection. Caution should be taken when using the contralateral ear as a control study investigating inner-ear drug delivery through the transtympanic approach.

The Effect of Patient Volume and Experience on Management of Menière's Disease

HYPOTHESIS

Treatment modalities administered by Otolaryngologists vary based on patient volume and years of experience.

OBJECTIVE

It was our goal to evaluate the current trends in treatment modalities administered by Otolaryngologists based on patient volume and years of experience.

METHODS

An electronic questionnaire was distributed to all General Otolaryngologists and fellowship-trained Neurotologist members of the American Academy of Otolaryngology-Head and Neck Surgery (AAO-HNS). Respondents were separated into groups by patients per year (<10, 10-29, 30-49, 50-99, or >100 patients) and years in practice (0-5, 6-10, 11-15, 16-20, or >20 yrs).

RESULTS

Eight hundred and sixty members replied for a response rate of 14.5% for generalists and 35% for neurotologists. Patient volume was found to have a positive association with perceived benefit of lifestyle and diet modification, and use of intratympanic steroids, intratympanic gentamycin, oral steroids, benzodiazepines, acetazolamide, endolymphatic sac procedures, vestibular nerve section, and surgical labyrinthectomy. Only endolymphatic sac procedures were found to have a significant positive association with a physician's length in practice. The only negative association was between intratympanic steroids and a physician's length in practice.

CONCLUSION

Physicians who see more MD patients annually are more likely to use these treatment modalities: diet and lifestyle modification, intratympanic steroids, intratympanic gentamycin, surgical labyrinthectomy, vestibular nerve section, acetazolamide, alprazolam, lorazepam, dexamethasone, and prednisone. Physicians with a longer length of time in practice are more likely to use only endolymphatic sac procedures, and they are less likely to use intratympanic steroids.