Open Source Content Management

February- November 2007 : Auditory Neuropathy

Details

Category: Guest editorial

Last Updated on Monday, 21 January 2013 15:15

Written by Ioannis Psaromatis, MD, PhD

Hits: 12796

Auditory Neuropathy : Introduction

Auditory Neuropathy: the torment of modern researchers and audiologists and a real challenge to their diagnostic abilities and their understanding of the auditory function.

         At the same time, auditory neuropathy might prove to be an excellent chance for breaking away from the standard audiological traditions and bridge together many scientific fields. It is very possible that the extremely familiar term sensorineural hearing loss will NOT have precise meaning in the near future.

Clinical approach to auditory neuropathy

     During the last few years, Auditory Neuropathy (AN) has been established as a well-accepted clinical entity. The term is ascribed to Starr et al  [1]who 10 years ago published the first report on AN. The data he discussed were based  on 10 patients having: (i) mild to severe hearing loss ; (ii) poor speech discrimination scores; (iii) absent or severely disturbed auditory brainstem responses (ABR); (iv) normal otoacoustic emissions (OAEs);and  (v) no central nervous system abnormalities . They have attributed their findings to a functional disorder of the acoustic nerve.  In this context it should be noted that Auditory Neuropathy-like cases had been reported several years earlier [2, 3, 4] The last decade the introduction of OAEs in the everyday clinical practice has resulted in diagnosing AN at increasing rates. It is not surprising, therefore, that numerous reports have appeared recently in the international literature.

     Today we use the definition for auditory neuropathy patients, whose clinical and audiological characteristics are summarized in Table 1. 

     However, there is no consensus about the term Auditory Neuropathy;. Neural synchrony disorder, brainstem auditory processing syndrome, central auditory dysfunction, auditory synaptopathy, auditory dys-synchrony and primary auditory neuropathy have also been used to describe patients showing similar audiological findinds.

     The prevalence of the recently described pathology known as ‘‘auditory neuropathy’’ in children with hearing loss has been reported to vary greatly, ranging between 0.5 and 24% [4, 5, 6, 7, 8, 9 ] while the prevalence of auditory neuropathy in the non-risk population is unknown. It is estimated that one in every ten children with hearing loss may suffer from auditory neuropathy [10 ].
     Concerning the etiology of auditory neuropathy, it is not well understood yet. Theoretically, all pathologies which affect transmission of the auditory signal from the level of inner hair cells to auditory cortex could give clinical and physiological evidences of what we today call “auditory neuropathy”. In such cases, if the necessary imaging studies fail to reveal a space occupying lesion or anatomic abnormalities [11] we can conclude that one or more intrinsic factors of the auditory pathway could account for these findings. Therefore, regardless the underlying pathology, auditory neuropathy may be considered as an intrinsic dysfunction of the auditory pathways. Patients meeting the profile of auditory neuropathy may be phenotypically healthy or they may suffer from various and seemingly dissimilar pathologies, including neonatal jaundice and anoxia, infections, neurologic, endocrine, metabolic and genetic diseases (Table 2> from references 9,12, 13, 14, 15, 16).   We can speculate that their harmful effect may be either: 

a) Segmental or localized, limited to a certain part of the auditory pathway (eg, otoferlin mutations that result in defective exocytosis of neurotransmitter at the synapses between inner hair cells and auditory nerve [17])
b) Multilevel or generalized, affecting a great part of the auditory pathway (eg, bilirubin-induced damages on auditory nuclei and probably auditory nerve [18, 19,]).

 

     According to the transmission patterns, auditory neuropathy could also be divided in a) genetic and b) non-genetic or acquired. Neonates suffering from hyperbilirubinemia and anoxia may develop acquired auditory neuropathy. On the contrary, mutations in the different chromosomes and genes have been reported to be the cause of autosomal dominant or recessive auditory neuropathy, either non-syndromic or accompanied with other inherited neuropathies [20, 21, 22, 23]. Recently, genetic studies [17, 24,25, 26] showed that mutations in otoferlin gene cause non-syndromic recessive auditory neuropathy by affecting calcium-mediated synaptic exocytosis of inner hair cells. Failure of neurotransmitter release blocks the auditory signals at the level of the synapses between inner hair cells and VIIIth nerve endings, thus resulting in a true “auditory synaptopathy”. Another study [27] has demonstrated that mutations in the gene encoding pejvakin, a newly identified protein of the afferent auditory pathway, cause DFNB59 auditory neuropathy. Since this protein is expressed not only in the cochlear sensory epithelium but in the cochlear nuclei, superior olivary complex and inferior colliculus as well, it is believed that it may have a role in the propagation of action potentials through auditory pathway and, consequently, its deficiency could be responsible for an auditory neuropathy phenotype.

        Prognosis of auditory neuropathy remains unpredictable. There are variable reports in the literature showing clinical or laboratory improvement of some patients [6, 28, 29] while others remain stable over time or even worsen, losing outer hair cells’ function [5, 30, 31]. Moreover, some patients may intermittently suffer from auditory neuropathy [32]. In a large series of high risk infants we found that most infants meeting the auditory neuropathy profile (13 out of 20, or 65%) demonstrated a restoration of their auditory neural transmission, that is normal ABR recordings on re-examination. Remarkably, recovery was significantly more common in infants with low birth weight [see reference 9 for details]. In any case, it becomes obvious that some subjects suffering from auditory neuropathy will get better but we are not able to accurately predict who will restore their auditory performance.

       The remarkable variation in the clinical and laboratory findings and the unpredictable prognosis observed in many auditory neuropathic patients makes their management difficult, without commonly acceptable “rules”. Audiologists and otologists should avoid a strict approach to this unexplained pathology. On the contrary, a flexible attitude must be adopted taking into account individual needs. It is author’s belief that in infants and young children behavioural tests should mainly direct the management of auditory neuropathy, not the results of physiologic tests. Hearing aids and cochlear implants are among treatment modalities but not all auditory neuropathy cases have the indication or would benefit from them.

         Studies have showed that only some of the patients suffering from auditory neuropathy would benefit from hearing aids [5 , 33 ]. Probably, these patients can hear but cannot understand [34]. If auditory neuropathy is purely an expression of de-synchronization of acoustic nerve signalling, then hearing aids do not represent the management of choice. Similar uncertainties and queries are encountered in cases treated with cochlear implantation. Some researchers have reported favourable outcomes while others have described poor speech perception scores in patients with auditory neuropathy who have received a cochlear implant [e.g., 5,35, 36, 37 ]. The site and severity of lesion (-s) and the underlying pathology may play a role for the observed diversity in surgical management of auditory neuropathy. It is also possible electric stimuli provided by the cochlear implant to re-synchronize auditory signalling, operating as a pacemaker for the auditory pathway.

Hearing screening programs and auditory neuropathy

      Since OAEs are generated within the cochlea, OAE-based hearing screening can not detect neural dysfunction. Consequently, infants with auditory neuropathy or neural conduction disorders without concomitant sensory (ie, outer hair cell) dysfunction will not be detected by OAEs [38]. In such cases OAEs will give false negative results. Babies treated in neonatal intensive care units are at increased risk for hearing loss, neural conduction and/or auditory brainstem dysfunction, including auditory neuropathy [38]. Probably OAEs do not represent the method of choice for screening high risk populations. The same could apply to all infants suffering from neurologic, metabolic, endocrine or central nervous system disorder, where a higher rate of central auditory dysfunction is expected. The impact of similar findings -that is the combination present OAEs/abnormal ABR- on neonatal hearing screening programs will probably lead to crucial changes in their schemes. Auditory brainstem responses (either automated or conventional) supplemented by OAEs in cases showing elevated thresholds, atypical or absent responses, may prove more effective methodology for screening high risk neonates. 

Case Studies

Case 1: Auditory Neuropathy with present acoustic middle ear reflex.

Comments: In patients suffering from auditory neuropathy acoustic middle ear reflex is typically absent. In this case, present OAEs (left) and absent ABR (top-right) in a phenotypically normal child 1 ½ years old are accompanied by present ipsilateral middle ear reflexes, bilaterally (bottom-right, arrows).The Acoustic stapedious muscle reflex can be present in patients suffering from auditory neuropathy. Tone-evoked stapedious reflex may not need the strict synchronization required for ABR recordings.

Case 2: Auditory neuropathy in a child with pituitary stalk interruption syndrome (PSIS)

Comments: Another unusual case of auditory neuropathy. A boy 2 years old was referred for audiologic evaluation due to a mild speech delay (first true words at the age of 15 months), mild hypotonia, clumsy walking and short stature. Auditory brainstem responses were consistent with severe to profound hearing loss bilaterally (top-left), TEOAEs were normal in both ears (top-right) while free-field audiometry suggested only mild hearing loss, if any. We did not recommend hearing amplification. At the same age (2y.o.) primary hypothyroidism was diagnosed. Physiologic tests were repeated at age 3 ½ yielding similar findings. Subjective tests revealed normal pure tone thresholds bilaterally (bottom-left) and near normal speech discrimination scores. Due to persistent short stature a detailed endocrine investigation was undertaken and growth hormone insufficiency was diagnosed. Pituitary MRI (bottom-right) was characteristic of pituitary stalk interruption with a hypoplastic anterior lobe of hypophysis (arrow) and a bright ectopic posterior lobe, just below the hypothalamus (arrowhead). The pituitary stalk is not visible. Today the child is 9 years old, he is under replacement therapy, he has never used hearing aids and he shows normal speech skills. The combination of PSIS and auditory neuropathy represents a poorly understood pathology of unknown pathogenetic mechanism. It could be attributed to genetic interactions during the fetal growth, between genes which are involved in the embryogenesis of hypophysis and those responsible for auditory neuropathy phenotype.

Conclusions

      Genetic or acquired, syndromic or non-syndromic, segmental or multilevel, permanent, transient or fluctuant, auditory neuropathy is an intrinsic dysfunction of auditory pathways with many unexplored aspects. We must first understand the underlying pathogenetic mechanism (-s) before drawing definitive conclusions about its terminology, etiology (-ies), prognosis and optimal management. Till then, the use of the controversial term “auditory neuropathy” probably represents the less offensive action among those we have taken for this disorder.

Key issues relative to AN

• Interpret a positive screening OAE-test cautiously, especially in neonates from ICUs

• Repeat physiologic tests in newborns diagnosed with auditory neuropathy at about 6 months of age

• Inform/educate parents adequately

• Individualize treatment plan

• Use behavioural tests for decision making concerning hearing amplification and cochlear implantation

• If hearing aids are recommended, consider monaural amplification, low maximum power output, close monitoring with OAEs

• If cochlear implantation is recommended, allow adequate time to elapse because CNS maturation or auditory function restoration may be in progress

• Be well-informed about the latest developments on the subject

References

1. A. Starr, T. Pincton, Y. Sininger, L. Hood, C. Berlin. Auditory neuropathy. Brain 119 (1996) 741-753. H. Davis, S.K. Hirsh. A slow brain stem response for low frequency audiometry. Audiology 18 (1979) 445-461.

2. H. Davis, S.K. Hirsh. A slow brain stem response for low frequency audiometry. Audiology 18 (1979) 445-461

3. D. Worthington, J. Peters, Quantifiable hearing and no ABR: paradox or error? Ear Hear. (1980) 1:281-285.

4. N. Kraus, O. Ozdamar, L. Stein, N. Reed. Absent auditory brain stem response: peripheral hearing loss or brain stem dysfunction? Laryngoscope 94 (1984) 400-406.

5. G. Rance, D. Beer, B. Cone-Wesson, R. Shepherd, R. Dowell, A. King, F. Rickards, G. Clark. Clinical findings for a group of infants and young children with auditory neuropathy. Ear Hear. 20 (1999) 238-252.

6. C. Madden, M. Rutter, L. Hilbert, J. Greinwald, D. Choo. Clinical and audiological features in auditory neuropathy. Arch. Otolaryngol. Head Neck. Surg. 128 (2002) 1026-1030.

7. C.I. Berlin, T. Morlet, L.J. Hood. Auditory neuropathy/dyssynchrony: its diagnosis and management. Pediatr. Clin. North Am. 50 (2003) 331-340.

8. A.L. Berg, J.B. Spitzer, H.M. Towers, C. Bartosiewicz, B.E. Diamond. Newborn hearing screening in the NICU: profile of failed auditory brainstem response/passed otoacoustic emission. Pediatrics 116 (4) (2005) 933-938.

9. Ioannis Psarommatis, Maria Riga, Konstantinos Douros, Petros Koltsidopoulos, Dimitrios Douniadakis, Ioannis Kapetanakis, Nikolaos Apostolopoulos. Transient infantile auditory neuropathy and its clinical implications. Int J Pediatr Otorhinolaryngol 70 (2006) 1629-1637.

10. Yvonne S. Sininger. Identification of Auditory Neuropathy in Infants and Children. Seminars in Hearing (2002) 23(3): 193-200.

11. Craig A. Buchman, Patricia A. Roush, Holly F. B. Teagle, Carolyn J. Brown, Carlton J. Zdanski, John H Grose. Auditory Neuropathy Characteristics in Children with Cochlear Nerve Deficiency. Ear & Hearing (2006) 27 (4): 399-408.

12. R. Tibesar, J.K. Shallop. Auditory neurapathy, in: C. Cummings, P. Flint, B. Haughey, T. Robbins, R. Thomas, L. Harker, M. Richardson, D. Schuller (Eds.), Otolaryngology: Head & Neck Surgery, 4th ed., Elsevier Mosby, Philadelphia, 2005, 3503-3521.

13. Y. Sininger, S. Oba. Patients with auditory neuropathy: who are they and what can they hear? in: Y. Sininger, A. Starr (Eds.), Auditory Neuropathy: A New Perspective on Hearing Disorders, Singular Press, San Diego, 2001, 15-35.

14: A. Starr. The neurology of auditory neuropathy, in: Y. Sininger, A. Starr (Eds.), Auditory Neuropathy: A New Perspective on Hearing Disorders, Singular Press, San Diego, 2001, 37-50.

15. Ceranic B, Luxon LM. Progressive auditory neuropathy in patients with Leber's hereditary optic neuropathy. J Neurol Neurosurg Psychiatry (2004) 75(4):626-30.

16. Beno?t Jutrasa, Laura J. Russell, Anne-Marie Hurteau, Martine Chapdelaine. Auditory neuropathy in siblings with Waardenburg’s syndrome. Int J Pediatr Otorhinolaryngol (2003) 67, 1133-1142.

17. Isabelle Roux, Saaid Safieddine,Regis Nouvian, M’hamed Grati, Marie-Christine Simmler, Amel Bahloul, Isabelle Perfettini, Morgane Le Gall, Philippe Rostaing, Ghislaine Hamard, Antoine Triller, Paul Avan, Tobias Moser, Christine Petit. Otoferlin, Defective in a Human Deafness Form, Is Essential for Exocytosis at the Auditory Ribbon Synapse. Cell (2006) 127, 277–289.

18. Wayne T. Shaia, Steven M. Shapiro, Robert F. Spencer. The Jaundiced Gunn Rat Model of Auditory Neuropathy/Dyssynchrony. Laryngoscope (2005) 115: pp 2167-2173.

19. Steven M. Shapiro. Definition of the Clinical Spectrum of Kernicterus and Bilirubin-Induced Neurologic Dysfunction (BIND). Journal of Perinatology (2005) 25:54–59

20. Perez H, Vilchez J, Sevilla T, Martinez L. Audiologic evaluation in Charcot-Marie-Tooth disease. Scand Audiol Suppl (1988) 30:211-13.

21. Bahr M, Andres F, Timmerman V, Nelis ME, Van Broeckhoven C, Dichgans J. Central visual, acoustic, and motor pathway involvement in a Charcot-Marie-Tooth family with an Asn205Ser mutation in the connexion 32 gene (in process citation). J Neurol Neurosurg Psychiatry (1999) 66:202-6.

22. Butinar D, Zidar J, Leonardis L, Popovic M, Kalaydjieva L, Angelicheva D, Sininger Y, Keats B, Starr A. Hereditary auditory, vestibular, motor, and sensory neuropathy in a Slovenian Roma (Gypsy) kindred. Ann Neurol (1999) 46:36-44.

23. Starr A, Michalewski HJ, Zeng FG, Fujikawa-Brooks S, Linthicum F, Kim CS, Winnier D, Keats B. Pathology and physiology of auditory neuropathy with a novel mutation in the MPZ gene (Tyr145->Ser). Brain (2003)126(7):1604-19.

24. Yasunaga S, Grati M, Cohen-Salmon M, El-Amraoui A, Mustapha M, Salem N, El-Zir E, Loiselet J, Petit C. A mutation in OTOF, encoding otoferlin, a FER-1-like protein, causes DFNB9, a nonsyndromic form of deafness. Nat Genet (1999) 21:363-9.

25. Varga, R., Kelley, P.M., Keats, B.J., Starr, A., Leal, S.M., Cohn, E., Kimberling, W.J. Non-syndromic recessive auditory neuropathy is the result of mutations in the otoferlin (OTOF) gene. J. Med. Genet. (2003) 40, 45–50.

26. Tekin M, Akcayoz D, Incesulu A. A novel missense mutation in a C2 domain of OTOF results in autosomal recessive auditory neuropathy. Am J Med Genet A (2005) 138:6–10.

27. Sedigheh Delmaghani, Francisco J del Castillo, Vincent Michel, Michel Leibovici, Asadollah Aghaie, Uri Ron, Lut Van Laer, Nir Ben-Tal, Guy Van Camp, Dominique Weil, Francina Langa, Mark Lathrop, Paul Avan, Christine Petit. Mutations in the gene encoding pejvakin, a newly identified protein of the afferent auditory pathway, cause DFNB59 auditory neuropathy. Nature Genetics (2006) 38 (7): 770-778.

28. L. Stein, K. Tremblay, J. Pasternak, S. Banerjee, K. Lindemann, N. Kraus. Brainstem abnormalities in neonates with normal otoacoustic emissions. Semin. Hear. 17 (2) (1996) 197-212.

29. Rhee Chung-Ku, Park Hyun-Min, Jang Yong-Ju. Audiologic Evaluation of Neonates With Severe Hyperbilirubinemia Using Transiently Evoked Otoacoustic Emissions and Auditory Brainstem Responses. Laryngoscope 109 (1999) 2005-2008.

30. J. Marko, A. Morant, M. Orts, M.I. Pitarch, J. Garcia. Auditory neuropathy in children. Acta Otolaryngol. 120 (2000) 201-204.

31. P. Deltenre, A.L. Mansbach, C. Bozet, F. Christiaens, P. Barthelemy, D. Paulissen, T. Renglet. Auditory neuropathy with preserved cochlear microphonics and secondary loss of otoacoustic emissions. Audiology 38 (1999) 187-195.

32. Starr, A., Sininger, Y. S., Winter, M., Dereby, M. J., Oba, S., Michalewski, H. J. Transient deafness due to temperature-sensitive auditory neuropathy. Ear and Hearing (1998) 19: 169-179.

33. Berlin C, Bordelon J, St John P, D. Wilensky, A. Hurley, E. Kluka, L.J. Hood. Reversing click polarity may uncover auditory neuropathy in infants. Ear Hear (1998) 19:37–47.

34. Zeng FG, Oba S, Sininger Y, Starr A. Temporal and speech processing deficits in auditory neuropathy, Neuroreport 10:3429–3435, 1999.

35. Peterson A, Shallop J, Driscoll C, Breneman A, Babb J, Stoeckel R, Fabry L. Outcomes of cochlear implantation in children with auditory neuropathy. J Am Acad Audiol. (2003) 14(4):188-201.

36. Rosamaria Santarelli, Pietro Scimemi, Erica Dal Monte, Elisabetta Genovese, Edoardo Arslan. Auditory neuropathy in systemic sclerosis: a speech perception and evoked potential study before and after cochlear implantation. Eur Arch Otorhinolaryngol (2006) 263: 809–815.

37. Miyamoto RT, Kirk KI, Renshaw J, Hussain D. Cochlear implantation in auditory neuropathy. Laryngoscope (1999) 109(2 Pt 1):181-5.

38. Joint Committee on Infant Hearing, Position statement: principles and guidelines for early hearing detection and intervention programs, Pediatrics (2000) 6(4): 798-817.

• < Prev
• Next >