A new method for Partial Deafness treatment ( PDT)
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- Category: Cochlear Implants and NHS
- Last Updated on Tuesday, 11 February 2014 08:49
- Written by Henryk Skarzynski MD, Artur Lorenz PhD
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1 Partial Deafness
In recent years, there has been a change of attitude towards cochlear implant candidacy criteria, resulting from the development of implant technology and growing expertise in surgery and rehabilitation. Today, not only individuals with the bilateral profound hearing loss are considered likely to receive a cochlear implant; also these with considerable residual hearing, or even normal hearing at low frequencies up to 1,5 kHz, are considered as candidates for cochlear implantation (Skarzynski et al., 2010). There is a large group of patients whose hearing impairment is characterized by normal or slightly elevated thresholds in the low-frequency band with nearly total deafness in higher frequencies. We proposed to describe this type of hearing impairment as partial deafness. Patients with good hearing only in the low frequencies are able to detect all the vowels, but probably few, if any, consonants. Low frequency perception can foster speech reading, speech production, and environmental sound awareness can contribute to the recognition of intended emotions. Notwithstanding, such hearing still does not allow patients the ability to communicate efficiently in everyday life, particularly in noisy listening situations. Often these patients remain beyond the scope of effective treatment with hearing aids only, since amplification at frequencies above the region of substantial residual hearing provides little or no benefit for individuals with partial deafness.
2 Cochlear Implantation in the partially deafened case
In 2002 our centre decided to implant a partially deafened young woman [Skarżyński, Lorens, Piotrowska; 2003]. The patient’s left ear was implanted with a Med-El Combi 40+ system, using the standard electrode array. To avoid loss of low-frequency hearing, a partial electrode insertion was performed, with an approach to the scala tympani directly through the round-window membrane. The approximated depth of insertion was 20 mm. Eight of the 12 electric contacts were inserted. The low frequency hearing was preserved to the large extend as proved by audiometric and ABR evaluation. The audiometric thresholds measured at 125 Hz and 250 Hz were the same as those measured preoperatively. After a short period following activation of the cochlear implant, a quite large and highly significant improvement in the recognition of monosyllabic words was observed.
Results from the first case supported further applications of cochlear implants for people with partial deafness [Skarżyński, Lorens, Piotrowska; 2003].
3 Partial Deafness Cochlear Implantation (PDCI)
Obtained results from the first partially deafened case were considered to be the first step towards the application of a partial deafness cochlear implantation (PDCI). To implement the method, a 3-step procedure was proposed, with pre-, intra- and post-operative parts [Skarżyński, Lorens, Piotrowska; 2003].
PDCI essentially involves 3 challenging aspects. 1) Careful selection of the right candidates most likely to gain substantial benefit from the procedure; 2) Surgical techniques allowing hearing preservation; and 3) transferring the maximum amount of sound information to the patient using an optimized configuration of electrical pulses to the electrodes combined with acoustic information.
The preoperative part of PDCI method includes clinical and audiological assessment to confirm fulfillment of qualification criteria, i.e., thresholds of 55 dB HL at 125, 250 and 500 Hz, and thresholds of 70 dB HL or higher at all higher audiometric frequencies. The subject should obtain limited benefit from the most-optimally fitted hearing amplification, with monosyllable scores in quiet of 55% correct or lower in both ears in the best-aided condition, at 60 dB SPL [Skarżyński, Lorens, Piotrowska; 2003].
The surgical procedure of PDCI proposed by Skarzynski consists of the following steps [Skarzynski et al. 2003, 2007a]:
1. Antrotomy
2. Posterior tympanotomy to allow for visualisation of the round window niche
3. Puncture the round window membrane
4. Approach the scala tympani directly through the round window membrane (with partial insertion of the electrode array)
5. Electrode fixation in the round window niche with fibrin glue (membrane must be partially uncovered to preserve its mobility)
6. Fixation of the device in the well created in the temporal bone
The postoperative part of PDCI method includes audiological assessment of preserved hearing sensitivity at low frequencies and cochlear implant system fitting, with the latter focused on selection of appropriate parameters of electrical stimulation. [Skarżyński, Lorens, Piotrowska; 2003]. We demonstrated that PDCI subjects were able to use their natural low-frequency hearing without amplification together with their cochlear implant (CI) to obtain outstanding results in speech tests. As there is only partial insertion of the electrode, careful consideration of programming the device is required. Only those electrodes inserted in the cochlea are activated and this is determined based on telemetry and reported hearing sensation. Frequency of electrodes is determined by the audiogram. The aim is to programm the cochlear implant without any overlap with acoustic perception, so as to not interfere with this perception. This is usually between 500Hz and 1000Hz. Electrode frequency modification can be adjusted on the cochlear implant fitting software [Lorens et al., 2008].
Encouraged by outstanding results achieved by application of electric and acoustic stimulation in adults the decision was made to perform partial deafness cochlear implantation in children in 2004 (Skarzynski et al. 2007). Our pediatric study results showed that hearing could be preserved partially in all cases. Speech perception tests showed improvement in quiet and noise over time. We demonstrated that children with partial deafness perform better than their pre-operative hearing aid conditions, even in instances where hearing could not be preserved completely.
4. Partial Deafness Treatment
The criteria for application of acoustic and electric amplification provided by the range of hearing aids, middle ear implants, and cochlear implants may complement one another.
The classification of partial deafness treatment (PDT) was first suggested by Skarzynski et al. 2010. The model is important for evaluating the post-implantation performance in homogeneous groups of patients with various levels of preoperative hearing. Results obtained in distinct groups of patients by authors using various assessment methods can provide valuable data for further widening PDT selection criteria and helping to establish it as a common intervention. All these advancements have resulted in the development and more widespread use of new technologies in postoperative care such as telemedical networks and other health services.
References
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