Utilization of a nerve integrity monitor to perform clinical promontory stimulation testing in cochlear implant candidacy

Elizabeth A. Kelly, MD1; Samuel Levine, MD1; Kristin E. Gravel, AuD2; Dianna L. Hart, AuD2; Tina Huang, MD1

1University of Minnesota, 2Fairview Health Services

INTRODUCTION DISCUSSION

RESULTS

Patient 1

Patient 2

Patient 3

Patient 4

Age (years old) 80 34 83 50

Duration of deafness 5 years 6 months 10 years 4 months

Etiology for hearing loss Congenital Trauma Hereditary NF 2

PST result positive positive positive negative

Received cochlear implant

(Y/N)Y Y N N

Auditory perception after

implantation (Y/N)Y Y N/A N/A

Table 1. Series of patients that underwent promontorystimulation testing using NIM. Abbreviations: NF2: neurofibromatosis type 2, PST: promontory stimulation testing, N/A: not applicable.

Figure 3. Promontory stimulator setup (ground electrodes typically placed on nape of patient’s neck)

Figure 1. Cochlear™ Nucleus Promontory Stimulator

ABSTRACT

METHODS AND MATERIALS

CONCLUSIONS

REFERENCES

CONTACT

Objectives: To demonstrate the feasibility of a nerve integrity monitor as a tool for promontory stimulation testing in patients with profound sensorineural hearing loss considering cochlear implantation.

Study Design: Retrospective case review.

Methods: Four patients with profound sensorineural hearing loss underwent promontory stimulation testing in the clinic setting to determine candidacy for a cochlear implant. By using a prass probe and the nerve integrity monitor, transtympanic promontory stimulation testing was performed to assess auditory nerve function. The stimulus amplitude was started at 0.01 mA and gradually increased, but did not exceed 0.3 mA. Patients indicated if they heard the stimulus.

Results: Of the four patients completing the promontory stimulation tests, 3 patients heard the stimulus and 1 patient did not hear the stimulus. Of the 3 patients with a positive stimulation test, 2 patients have a history of progressive profound sensorineural hearing loss and 1 patient had a history of severe blunt temporal bone trauma. Two of these patients proceeded with cochlear implantation. The patient that had a negative promontory stimulation test has a history of neurofibromatosis 2 and is currently being considered for an auditory brainstem implant. The testing was performed without difficulty using the prass probe and nerve integrity monitor.

Conclusions: The nerve integrity monitor is a convenient tool used in the clinic setting to perform promontory stimulation tests and aid in determining cochlear implant candidates, specifically in those patients that require verification of auditory nerve function. This tool is a feasible and appropriate method for promontory stimulation testing.

• 67 patients seen for CI evaluation during study period. • 4 patients àPST to aid in assessment of CI

candidacy (Table 1).• 3 of the 4 patients àpositive testing. • 2 of the 3 àCI.

• Patient #1 - Reported auditory stimulation at 2 month follow up visit.

• Patient #2 – CI complicated by cochlear ossification, requiring drill out. • Sound awareness at 2 month follow up.• Adjusting programming to improve

outcomes. • Both communicated by listening and lip-

reading after CI.

• Need to assess auditory nerve function during cochlear implant candidacy is rare. • 6% in our series• PST equipment has become outdated and

difficult to maintain à limitations in the full assessment of patients prior to surgery.

• Majority of patients with positive result

• NIM is an alternative technique to perform promontory stimulation• Used in other otologic procedures.4• Convenient and available.• Inexpensive• FDA approved equipment, however would

be an off label use of the equipment.• Same settings as original PST box.

• PST remains beneficial:• Role in preoperative counseling for CI.5-7

• Predict post operative speech reception.3,8,9

• May guide decisions in which side to implant in unilateral cases.8

• Disadvantages of study• Small sample size

• Not demonstrating the sensitivity of PST but introducing a new convenient method to perform this testing.

• False negatives reported with PST.• Related to thickness of otic capsule in

some patients, or inability to completely visualize placement of electrode.6

• The use of NIM for this test does not address these issues but would give a patient and provider additional information prior to proceeding with CI.

• Retrospective case review from Dec 2014 to Dec 2015.

• Approved by IRB at University of Minnesota.Inclusion criteria:

• Presented for cochlear implant evaluation.• Unmeasurable responses on audiometric

testing.• Proceeded with transtympanic promontory

stimulation testing NIM.

Transtympanic promontory stimulation testing • Audiologist and Neurotologist present for

testing.• Office based procedure.• Ground electrode stickers placed a patients

neck (Figure 1).• Performed with NIM (Figure 2).

• Reset the default stimulation profile• Saved these settings in a new profile:

monopolar stimulation, pulse rate 1/second, pulse width 250 µs.

• Tympanic membrane topically anesthetized. • Posteroinferior myringotomy performed. • Prass probe inserted and placed on

promontory.• Stimulus amplitude started at 0.01 mA (not

exceeding 0.3 mA).• Positive test:

• Heard the stimulus.• Tapped out pulsations. • Identified when no stimulus.

• Negative test: No auditory sensation.

1. House WF, Brackmann DE. Electrical promontory testing in differential diagnosis of sensori-neural hearing impairment. Laryngoscope. 1974;84(12):2163–2171.

2. Kileny PR, Zwolan TA, Zimmerman-Phillips S, Kemink JL. A comparison of round-window and transtympanic promontory electric stimulation in cochlear implant candidates. Ear Hear. 1992;13(5):294–299.

3. Kuo SCL, Gibson WPR. The role of the promontory stimulation test in cochlear implantation. Cochlear Implants Int. 2002;3(1):19–28.

4. Heman-Ackah SE, Gupta S, Lalwani AK. Is facial nerve integrity monitoring of value in chronic ear surgery? Laryngoscope. 2012;123(1):2–3.

5. Greenberg SL, Shipp D, Lin VY, Chen JM, Nedzelski JM. Cochlear implantation in patients with bilateral severe sensorineural hearing loss after major blunt head trauma. Otol. Neurotol. 2011;32(1):48–54.

6. Kileny PR, Zimmerman-Phillips S, Kemink JL, Schmaltz SP. Effects of preoperative electrical stimulability and historical factors on performance with multichannel cochlear implant. Ann. Otol. Rhinol. Laryngol. 1991;100(7):563–568.

7. Cueva RA, Thedinger BA, Harris JP, Glasscock ME. Electrical promontory stimulation in patients with intact cochlear nerve and anacusis following acoustic neuroma surgery. Laryngoscope. 1992;102(11):1220–1224.

8. Lee JC, Yoo MH, Ahn JH, Lee K-S. Value of the promontory stimulation test in predicting speech perception after cochlear implantation. Laryngoscope. 2007;117(11):1988–1992.

9. Alfelasi M, Piron JP, Mathiolon C, et al. The transtympanic promontory stimulation test in patients with auditory deprivation: correlations with electrical dynamics of cochlear implant and speech perception. Eur Arch Otorhinolaryngol. 2013;270(6):1809–1815.

Elizabeth KellyUniversity of MinnesotaEmail: kell1658@umn.edu

Promontory electrical stimulation testing (PST) was initially introduced by House and Brackman as a method to differentiate patients with sensory hearing loss from those with neural hearing loss.1 In cochlear implantation (CI), the vestibulocochlear nerve needs to be intact for a successful outcome. Both cochlear dysfunction and vestibulocochlear nerve loss can result in a clinical finding of a no-response audiogram. PST administers an electrical stimulation on the cochlear promontory to elicit an auditory response (Figure 1).

PST equipment is now outdated, difficult to troubleshoot and maintain. There are situations when PST continues to be beneficial. A more sensitive objective measure of the auditory function in these patients has yet to be developed.2,3 An ideal test of auditory nerve function would be minimally invasive, easily accessible, and inexpensive. Facial nerve monitoring is more common in otologic procedures with use of a nerve stimulator built into Medtronic neural integrity monitor (NIM).4The NIM is convenient, available, and FDA approved (Figure 2).

We plan to identify and describe a feasible method to perform PST. We aim to demonstrate that with the appropriate settings, the NIM may be used as a clinical tool to perform promontory stimulation testing when assessing cochlear implant candidacy in specific patients.

Promontory stimulation testing is rarely needed but has a significant role in detecting auditory neuron function. The subjective detection of auditory sensation is suggested to predict patients that will benefit from CI. The utilization of the NIM to perform PST provides a feasible and practical method to obtain this information.

• Retrospective case review from Dec 2014 to Dec 2015.

• Approved by IRB at University of Minnesota.

Inclusion criteria:• Adult patients for CI evaluation.• Unmeasurable responses on audiometric

testing (unaided/aided condition).• Transtympanic PST via NIM.

Transtympanic promontory stimulation testing • Audiologist and Neurotologist present.• Office based procedure.• Ground electrode stickers placed on

patient’s neck (Figure 3).• NIM

• Reset the default stimulation profile• Saved new profile: monopolar

stimulation, pulse rate 1/second, pulse width 250 µs.

• Patients instructed to indicate if heard any sound.

• Topical anesthetic to tympanic membrane. • Posteroinferior myringotomy performed. • Insert Prass probe, place on promontory.• Stimulus amplitude started at 0.01 mA (not

exceeding 0.3 mA).• Positive test:

• Heard the stimulus• Tapped out pulsations• Identified when no stimulus.

• Negative test: No auditory or only tactile sensation.

Figure 2. Medtronic NIM®

Nerve Monitoring system

ACKNOWLEDGEMENTSFrank H. Grovenstein, a Medtronic representative, helped establish the protocol.

No financial disclosures or conflicts of interest.