Facial nerve stimulation by a cochlear implant in a hemodialysis patient with bone of low mineral density

Apical Reference Stimulation: A Possible Solution to Facial Nerve Stimulation

OBJECTIVES

Postimplantation facial nerve stimulation is a common side-effect of intracochlear electrical stimulation. Facial nerve stimulation occurs when electric current intended to stimulate the auditory nerve, spread beyond the cochlea to excite the nearby facial nerve, causing involuntarily facial muscle contractions. Facial nerve stimulation can often be resolved through adjustments in speech processor fitting but, in some instances, these measures exhibit limited benefit or may have a detrimental effect on speech perception. In this study, apical reference stimulation mode was investigated as a potential intervention to facial nerve stimulation. Apical reference stimulation is a bipolar stimulation strategy in which the most apical electrode is used as the reference electrode for stimulation on all the other intracochlear electrodes.

DESIGN

A person-specific model of the human cochlea, facial nerve and electrode array, coupled with a neural model, was used to predict excitation of auditory and facial nerve fibers. These predictions were used to evaluate the effectiveness in reducing facial nerve stimulation using apical reference stimulation. Predictions were confirmed in psychoacoustic tests by determining auditory comfort and threshold levels for the apical reference stimulation mode while capturing electromyography data in two participants.

RESULTS

Models predicted a favorable outcome for apical reference stimulation, as facial nerve fiber thresholds were higher and auditory thresholds were lower, in direct comparison to conventional monopolar stimulation. Psychophysical tests also illustrated decreased auditory thresholds and increased dynamic range during apical reference stimulation. Furthermore, apical reference stimulation resulted in lower electromyography energy levels, compared to conventional monopolar stimulation, which suggests a reduction in facial nerve stimulation. Subjective feedback corroborated that apical reference stimulation alleviated facial nerve stimulation.

CONCLUSION

Apical reference stimulation may be a viable strategy to alleviate facial nerve stimulation considering the improvements in dynamic range and auditory thresholds, complemented with a reduction in facial nerve stimulation symptoms.

Evaluation of simplified programs using the MED-EL C40+ cochlear implant

The present study evaluated the benefit possible from a cochlear implant (CI) using a simplified map (with a set of default parameters), rather than the conventional approach of producing a 'customized map' from electrode-specific psychophysical measures. Young children are sometimes initially provided with such maps and the aim was to gain an insight into what level of benefit they might provide. Maps with upper stimulation levels set equally across the array (i.e. 'flat' maps) were compared with normal 'customized' maps in established adult users of the MED-EL C40+ device. Speech discrimination was significantly poorer for the flat maps overall (mean of 72.7% for customized map, and 60.5% for flat map) and loudness balance estimates showed a range of degrees of imbalance. These results suggest that flat maps may provide paediatric CI users with useful levels of performance when psychophysical or objective measures cannot be obtained. The poorer performance with the flat map suggests that customized maps should be fit as soon as possible to provide paediatric patients with the maximum benefit of the CI device.

Three-year follow-up of children with postmeningitic deafness and partial cochlear implant insertion

OBJECTIVES

To evaluate the long-term outcome of children with postmeningitic deafness and partial insertion of the Nucleus electrode array, and to compare their speech perception performance with that of children with full insertion of the electrode array.

DESIGN

A battery of seven speech perception tests was administered to 25 children with a cochlear implant (CI). Results were reduced into one score: equivalent hearing loss (EHL).

SETTING

Tertiary referral centre.

PARTICIPANTS

The partial insertion group comprised seven children, mean age at implantation 5.5 years, mean duration of deafness 3.6 years. The full-insertion control group comprised 18 children. Mean age at implantation: 4.4 years; mean duration of deafness: 2.9 years. All the children became deaf between 0 and 3 years of age.

MAIN OUTCOME MEASURES

Over a 3-year follow-up period, the children with partial insertion showed continuing progress, although there was wide variation in performance and the rate of progression. Some open-set comprehension could even be achieved with the insertion of only eight electrodes of a nucleus device.

RESULTS

Three years after implantation, speech perception in the partial insertion children was poorer than that in the control groups with long (P < 0.01; 95% confidence interval 7-43 dB EHL) and short duration of deafness (P < 0.0001; 95% confidence interval 28-53 dB EHL). They showed slower progress and reached a poorer EHL plateau. Four of the seven children acquired open-set word recognition.

CONCLUSIONS

Patients with partial insertion of the electrode array benefit from a CI, although less than patients with complete insertion.

Resolution of Facial Stimulation in Otosclerotic Cochlear Implants

OBJECTIVES: We examined the incidence of facial nerve stimulation in a population of patients with otosclerosis implanted with the Nucleus 22, Clarion 1.2, or Clarion High Focus (CHF) device.

STUDY DESIGN AND SETTING: A retrospective chart review was used for 147 patients who had been implanted with electronic cochlear devices at the University of Minnesota between June 1986 and February 2001. Seventy-four patients were implanted with the Nucleus 22, 41 patients were implanted with the Clarion 1.2 (without a positioner), and 32 patients were implanted with the CHF I or II.

RESULTS: Eleven (14.9%) of the 74 patients implanted with the Nucleus 22 device had facial stimulation. There were 9 patients with otosclerosis. Seven (78%) of the 9 patients with otosclerosis had facial stimulation. One (2.4%) of the 41 patients implanted with the Clarion 1.2 device (without a positioner) had facial stimulation and that 1 (100%) patient in the group had otosclerosis. There were 4 patients in the CHF group with otosclerosis. One patient experienced stimulation, but it was possible to decrease maximum current levels and still use the electrode pair.

CONCLUSION: Facial stimulation appears to be less problematic in patients with otosclerosis implanted with the CHF devices.

Spontaneous cerebrospinal fluid rhinorrhea associated with chronic renal failure--case report

A 39-year-old woman was admitted with complaints of headache and nasal discharge on the left for 3 months which was later on proved to be cerebrospinal fluid (CSF). Neurological examination found no abnormalities except bilateral papilledema. Neuroimaging demonstrated enlargement of the lamina cribrosa foramina through which the olfactory nerves pass, as well as empty sella and cerebral cortical atrophy. Bone mineral densitometry showed osteopenia. CSF Ca++ and blood parathyroid hormone levels were elevated. CSF pressure was 280 mmH2O. Bilateral frontal craniotomy was performed to expose the anterior fossa. Foraminal enlargement at the lamina cribrosa was confirmed, and islands of extra-osseous calcifications on the arachnoid membrane were identified. The base of the anterior fossa was repaired intradurally with fascial graft and fibrin glue on both sides. No CSF leakage was noted at 1-year follow up. Spontaneous CSF leakage probably resulted from enlargement of the foramina at the lamina cribrosa due to Ca++ mobilization from bones and pseudotumor cerebri not to the extent of hydrocephalus caused by poor CSF absorption at the arachnoid granulations obliterated by extra-osseous calcareous accumulation.