Pediatrics International (2014) 56, 400–405
Cochlear implant after bacterial meningitis Jesper Bille and Therese Ovesen Department of Otorhinolaryngology, Head and Neck Surgery, Aarhus University Hospital, Aarhus, Denmark Abstract
Background: The aim of this retrospective case study at a tertiary referral center was to investigate the outcome of cochlear implantation (CI) in children with sensorineural hearing loss due to meningitis compared to CI in children with deafness due to other reasons. Methods: This post-meningial group (PMG) consisted of 22 children undergoing CI due to deafness induced by meningitis, between December 1996 and January 2012. Five children had bilateral simultaneous implantation. None was excluded and the children were followed for at least 3 years. Operations were carried out by one of two surgeons using similar techniques in all cases. Each patient from the PMG was matched 2:1 with children having implantation for other reasons according to age and follow up (control group). Results: Overall, the median category of auditory performance (CAP) and speech intelligibility rating (SIR) score were not statistically significantly different between the two groups. The presence of additional central nervous system (CNS) disorders (post-meningeal sequelae), however, correlated significantly with poorer outcome Conclusions: CI was a safe procedure without surgical complications in the present study. It is possible to restore auditory capacity and speech performance to a degree comparable to children undergoing implantation for other reasons. A statistically important variable is secondary CNS involvement. The rehabilitation program after CI should be adjusted according to these additional handicaps. It is recommended to screen meningitis patients as fast as possible to identify those with hearing loss and initiate treatment with hearing aids or CI.
Key words bacterial meningitis, category of auditory performance, cochlear implantation, control group, speech intelligibility rating.
Cochlear implantation (CI) is the standard treatment of profound post-meningeal sensorineural hearing loss (SNHL) with the purpose of regaining auditory capability as well as speech performance (Fig. 1). It is possible for children to undergo implantation from the age of 4 months in order to reduce the period without auditory stimulation.1 Bacterial meningitis is the most common course (7–35%) of acquired postnatal SNHL.2–7 The most prevalent etiologic agents of bacterial meningitis are Streptococcus pneumoniae and Neisseria meningitidis.8 The risk of developing SNHL from N. meningitidis is much lower than that of S. pneumoniae.9 The pathogenesis of the SNHL is bacterial damage to the organ of Corti due to inflammation, subsequent fibrosis and potential ossification.3 The acute stage is characterized by purulent effusion followed by formation of sero-fibrinous precipitates. The second, fibrous stage occurs approximately after 2 weeks and is marked by fibroblastic proliferation and angiogenesis. Labyrinthitis ossificans, the last stage, shows new bone formation, often initiated in the basal turn. This last stage is seen as early as 2 months after the onset of meningitis and is
described in up to 70% of the ears.10,11 The ossification challenges the implantation and thereby also the outcome due to the risk of only partial insertion of the electrode or even impossible insertion. From a theoretical viewpoint, excellent results should be achievable with CI in patients suffering from post-meningeal SNHL provided that the neurons in the spiral ganglion and the more central neuronal networks remain intact and wellfunctioning. This may, however, not be the case in patients with more extensive brain damage, which occurs in up to 20–30% of post-meningeal children.12 CI may be postponed due to latency with regards diagnosis of SNHL or even lack of knowledge among professionals of the possibility of CI. Regardless of ossification, long time to implantation may impede the results. The primary aim of the present study was to compare the outcome of CI in children with deafness due to bacterial meningitis with children undergoing implantation for other reasons, in terms of capacity of auditory performance (CAP) and speech intelligibility rating (SIR). Secondary parameters were surgical complications and the effects of additional CNS involvement as well as the time interval between meningitis and CI.
Correspondence: Therese Ovesen, DMSc, Department of Otorhinolaryngology, Head and Neck Surgery, Aarhus University Hospital, Noerrebrogade 44, DK-8000 Aarhus C, Denmark. Email: [email protected]
rm.dk Received 25 April 2013; revised 5 July 2013; accepted 28 October 2013.
© 2013 The Authors Pediatrics International © 2013 Japan Pediatric Society
The medical records of 286 consecutive children younger than 15 years who underwent CI between December 1996 and January 2012 were reviewed and diagnosis, age, gender, comorbidity and etiology of SNHL were registered. Twenty-two children (8%)
Cochlear implant after meningitis
A 2:1 control group (CG) was randomly selected among the remaining 264 children and matched with the PMG in terms of age at implantation and follow up. The primary outcomes were postoperative CAP and SIR scores. The CAP and SIR test were performed by the speech therapist training the children according to standard procedures. The CAP test consists of eight performance categories arranged in order of increasing difficulty, with very high inter-user agreement making the CAP test a reliable tool in measuring the auditory capacity after CI.13,14 The SIR test consists of a rating from 1 to 5 with increasingly advanced language, and is a valid tool for testing children’s speech intelligibility after CI.14,15 As secondary parameters and variables, the following were registered: age at CI, time to implantation (from meningitis to CI: TTI), surgical complications, degree of ossification, additional CNS sequelae due to the meningitis, insertion depth, and number of active electrodes inside the cochlea. Statistical analysis
For comparison of the CAP and the SIR scores between subgroups and control group, the Mann–Whitney U-test was used with a significance level of 5%.
Fig. 1 1, sound waves are collected by the small, directional microphone located in the ear level processor; 2, the speech processor filters, analyzes and digitizes the sound into coded signals; 3, the coded signals are sent from the speech processor to the transmitting coil; 4, the transmitting coil sends the coded signals as FM radio signals to the cochlear implant under the skin; 5, the cochlear implant delivers the appropriate electrical energy to the array of electrodes inserted into the cochlea; 6, the electrodes along the array stimulate the remaining neurons in the cochlea; 7, the resulting electrical sound information is sent through the auditory system to the brain for interpretation. (Published with permission from Cochlear/ Danaflex, Denmark.)
were identified with post-meningeal SNHL. Preoperative computed tomography (CT) was available in all cases, magnetic resonance imaging (MRI) in nine. Either uni- or bilateral intracochlear ossification was identified in eight patients (31%). No additional cases of ossification were found per-operatively. Fifteen children in the post-meningeal group (PMG) had bilateral implantation (five simultaneously). Two surgeons had performed all the implantations by standard procedures and approach using a Nucleus Freedom CI24 or Nucleus CI512 electrode (Cochlear, Sydney, NSW, Australia), except in one case in which a split electrode (CI+11 + 11 + 2M) was used.
The characteristics of the PMG, including additional handicaps, are listed in Table 1. All PMG patients were deaf due to S. pneumoniae. Eighteen children were pre-lingual deaf defined by their age at meningitis (/≤1 year showed a tendency towards better scores in patients undergoing implantation within 1 year after the meningitis, which, however, was not statistically significantly different (median CAP: 5, range, 2–5 vs 7, range, 3–7; and median SIR: 3, range, 1–5 vs 4, range, 2–5; P = 0.33 and P = 0.28, respectively). A nonsignificant tendency towards better scores was also found in the case of complete insertion (median CAP: 7, range, 0–7 vs 4, range, 3–5; median SIR: 4, range, 1–5 vs 2, range, 1–4). Additional handicaps were found in seven patients (32%) in the PMG. The CAP and SIR scores were significantly lower among these seven children compared to the remaining 15 children in this group (median CAP: 4, range, 0–5 vs 7, range, 5–7; median SIR: 2, range, 1–3 vs 4, range, 2–5; P = 0.0006 and P < 0.0008, respectively, Mann–Whitney U-test).
Discussion Overall, the present study has demonstrated similar outcomes after CI in terms of auditory performance and speech capacity among children with deafness due to meningitis and children with deafness due to other reasons. The findings are in accordance with previous conclusions reported by Francis et al. and Nikolopoulos et al.16,17 In contrast, the present study involved comparison with a 2:1 control group and had a longer follow-up period. Furthermore, no patients were lost at follow up and all implantations were performed by two almost equally experienced surgeons using the same surgical approach and standard electrodes. In accordance with the present results, previous studies have found no significant differences in outcome in relation to the degree of ossification.18 Furthermore, other studies reported no correlation between time after meningitis and development of ossification.19 Not all patients had MRI, due to the fact that this was not standard procedure at the time they underwent implantation. Both MRI and CT, however, are today standard preoperative modalities in Denmark. As shown by numerous other studies, MRI is becoming the gold standard in the early screening of post-meningitis patients to identify signs of ossification.4,20–24 Ossification may occur within a few months after meningitis and may impede implantation or even render electrode insertion impossible. We did not exclude any candidates from CI, regardless of whether it could be achieved completely or partially due to ossification. Only two of the patients had implantation within 2 months after meningitis and therefore it was difficult to differentiate TTI more accurately in the present study. Nonetheless, there was a tendency towards better results with short TTI. Follow up was generally long, which may explain the lack of statistical difference between the PMG and the CG. This could be interpreted as the children with deafness due to meningitis catching up, in time, after CI, with the children with deafness due to other reasons. In contrast, Baraff et al. found no statistical evidence between early and late follow up in their meta-analysis from 1993.7 Accordingly, it may be hypothesized that the damage to the cochlear sensory epithelium as well as to the neurons, occurs early in the course of the meningitis without further progression © 2013 The Authors Pediatrics International © 2013 Japan Pediatric Society
and without relation to the ossification process. Early audiologic examination including cochleography and brainstem audiometry after meningitis is therefore mandatory to identify deafness, and CI is, under all circumstances, recommended as early as possible due to late-onset ossification and to achieve optimum performance. This is as recommended by the Dutch consensus protocol from 2010.25 We chose to measure CAP and SIR in order to obtain data comparable to international studies. The classification of the individual levels of performance, however, is rigid and hampered by the so-called ceiling effect, that is, the test persons do easily reach the highest scores. Therefore, the test battery ought to include more differentiated, but also more time-consuming and resource demanding, procedures in the future. To our knowledge, there are no previous studies demonstrating the significance of additional handicaps on the outcome of post-meningeal deafness with a long follow up, although such a correlation seems evident. These handicaps, especially those affecting cognitive skills, may increase the need for and extent of auditory as well as speech rehabilitation following CI, including the adjustment of the parents’ expectations. Conclusion
Cochlear implantation was found to be a safe procedure without surgical complications in patients with deafness due to meningitis. CI was possible in all cases despite abnormal CT demonstrating intra-cochlear ossification. The PMG outcome showed that hearing as well as speech capacities were restored to levels comparable to children with deafness due to other reason than meningitis. A statistically significant variable to consider is the presence of secondary CNS involvement, which was associated with poorer results in this group. This ought to be taken into account prior to implantation to ensure an optimum course of rehabilitation as well as adjustment of the parents’ expectations. It is therefore recommended to perform audiologic assessment in meningitis patients as fast as possible to identify hearing loss and eventually to offer CI.
Acknowledgment The authors state no conflicts of interest.
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© 2013 The Authors Pediatrics International © 2013 Japan Pediatric Society