auditory neuropathy spectrum disorder

auditory neuropathy,auditory dys-synchrony

1. AUDITORY NEUROPATHY SPECTRUM DISORDER Dr Anusree A Karun 2 nd yr DLO UIORL Madras Medical College Chennai

2. 27 yr old female presented to our OPD with chief complaints of Hard of hearing – right side *8 yrs Vertigo *8 yrs Tinnitus-right side * 5 yrs

3. O/E GPE- Normal ,,all pripheral nerves intact –ear –external-normal - eac ,tm- intact Tuning fork tests (R) (L) Rinne - + ve + ve Weber- lateralised to left ABC- reduced not reduced Vestibular funtion tests –normal No cerebellar signs No nystagmus Facial nerve bilateral normal

4. PTA-bilateral mild SNHL Pure tone average right ear -38.3dB HL left ear-38.3dB HL

5. Previous PTA -2015

6. PTA -2014

7. IMPEDENCE – bilateral reflexes were absent no e/o middle ear pathology Speech audiometry tests- Speech reception threshold- right-50dB HL left-50dB HL Speech discrimination score – right -30% left -35%

8. OAE-bilateral OHC functional BERA - for all five waves peaks could not be obtained at 90dB HL for click stimuli at a repetition rate of 11.1 clicks per seconds -Wave morphology & replicability was poor CERA -prolonged latency and reduced amplitude -abnormal waves

9. ….Hearing ,feeling but never truly comprehending Audiologic evaluation revealed …. HEARING LOSS AND SPEECH INTELLIGIBILTY SCORES OUT OF PROPORTION TO HER PRESUMED HEARING LOSS Progressive ANSD

10. Only treatment options left with us to address her complaints were– SPEECH ENHANCING STRATEGIES COMMUNICATION STRATEGIES ASSERTIVE TRAINING As she was not ideal for a hearing aid or implantation considering her magnitude of hearing loss

11. AUDITORY NEUROPATHY or AUDITORY DYSSYNCHRONY Describes a diagnosis with observations of inconsistent measures of hearing, i.e. where hearing sensitivity is better than might have been expected from the acoustic brainstem evoked responses

12. Cochlear amplification is preserved in these individuals, but discharges from the auditory nerve is asynchronous Synchronous firing of auditory nerve fibers is important for extracting complex acoustic features such as spectral peaks and waveform envelopes for speech recognition. The inability to follow temporal fluctuations is an important cause for poor speech perception in individuals with ANSD

13. …... characterised by Normal outer hair cell function evidenced by normal EOAE and / or cochlear microphonics responses coupled with absent or severely abnormal ABR responses Pure tone audiogram may range from normal to profound hearing loss Elevated or absent middle ear reflexes

14. Impaired speech discrimination scores and increased speech reception thresholds Rule out central auditory processing disorders Binaural intergration and seperation Monoaural low redundacy speech Temporal resolution measurement gap in noise test amplitude modulation detection test LLR

15. PREVALENCE Overall prevalence rare- 1-3 children per 10,000 births 40% in neonates with high risk for HL 2-15% in children with known hearing loss 1 in 10 children with hearing loss and severely abnormal BERA

16. PREVALENCE Our data shows (study conducted in rgggh mmc ISH 2010-2012) prevalence of ANSD among sensory neural hearing impaired is not rare but accounts for 5.06% Prevalence among children undergoing screening -0.42%

17. More common in children 50 % of all cases and 92 % of all bilateral cases manifests before 4 yrs of age Late onset ANSD –Rare incidence

18. RISK FACTORS Neonatal history of anoxia hyperbilirubinemia mechanical ventilation Congenital brain abnormalities Low birth weight Extreme Prematurity- < 28 wks Genetic or family history of AN/AD Also seen in association with Viral diseases , seizure disorders, high grade fever

19. ETIOLOGY Abnormality causing AN/AD resides in the lower auditory system- specifically damaged inner hair cells abnormal IHC - auditory nerve synapse the spiral ganglion neurons or the axons or dendrites of the auditory nerve itself. Reduced neuronal populations in brainstem

20. Mutation in otoferlin - most common genetic cause of non syndromic AN Otoferlin is a calcium detector for exostosis –required for replenishment of vesicles in active regions Absence of functional otoferlin protein selectively affects the inner hair cell synapse, resulting in profound deafness with preserved OHC function .

21. Etiology and associated conditions A mutation(overexpression) in DIAPH3 causes nonsyndromic dominant AN- defect of inner hair cell stereocilia and loss of synapses results in this phenotype Syndromic neuropathies– 1.Friederich ataxia(normal wave1 & middle ear auditory symptoms reflexes,indicating brainstem anomaly and not manifests first auditory nerve or IHC) occurs as a part of 2.charcot Marie tooth disease generalised neural 3.Lebers hereditary optic neuropathy deterioration 4.Stevens– johnson syndrome 5.Ehler danlos syndrome.

22. Etiology and associated conditions Aplasia or sometimes hypoplasia of the auditory nerve with normal cochlear morphology may also lead to an AN phenotype . Any neurotoxic environmental insult -including chemotherapeutic agents, hyperbilirubinemia -( damages brainstem cochlear nuclei, auditory nerve, superior olivary complex, lateral lemniscus , trapezoid bodies, inferior colliculus ) or anoxia.

23. Treatment Hearing normal - Speech pathology SPEECH ENHANCING STRATEGIES COMMUNICATION STRATEGIES ASSERTIVE TRAINING Hearing aid trial for language learnin g Cochlear implant when No improvement seen with HA - - helps in improving speech comprehension and language acquisition -CI provided consistent neural firing and the stimulus promotes neural survival and restore temporal activity . -Those with good temporal residual processing and normal LLR performed well Brainstem implant -when auditory nerve is aplastic or absent

24. Our statistics COMPLAINTS PTA SRT SISI ART OAE BERA 21/f L HOH Reduced clarity of speech R Mild low frequency SNHL L moderate low frequency SNHL R-75dB L-80 dB R-18% L-8% B/L I/L &C/L -VE + AbN 2 1/2/F Not respondng to loud sounds since birth Not done Not done Not done Not done + AbN 22/m R Mild low frequency SNHL L minimal frequency SNHL R-50dB L-60 dB R-20% L-18% B/L I/L &C/L -VE + AbN

25. Our statistics COMPLAINTS PTA SRT SISI ART OAE BERA 14/f B/L HOH B/L Severe SNHL R-90dB L-90 dB R-80% L-85% B/L I/L &C/L -VE + AbN 25/M B/L HOH B/L Moderate SNHL R-85dB L-85 dB R-0% L-0% B/L I/L &C/L -VE + AbN 24/m B/L HOH R profound SNHL L severe SNHL R-70dB L-65 dB R-0% L-0% B/L I/L &C/L -VE + AbN

26. One child benefited with cochlear implant Majority of the remaining benefited with hearing aid One pt with severe speech recognition difficulty but with mild hearing loss managed with speech enhancing strategies

27. Those with good residual temporal processing particularly amplitude modulation detection seems to be associated with significant benefit from hearing aids / cochlear implant Late onset ANSD benefits more from hearing aid as they would have had a long period of normal period of normal hearing Those with normal LLR benefitted well with hearing aid / cochlear implants

28. Central auditory deafness –a continuum that includes cortical deafness ,word deafness and auditory agnosia BERA normal ,CERA abnormal – cortical deafness -primary auditory cortex of brain affected bilaterally –most commonly due to stroke- Pt aware of their deficit ,non verbal sounds identified,defective language comprehension and repition BERA MLR LLR normal - Auditory agnosia –secondary and tertiary auditory cortex of brain(R hemisphere lesion)- Pt unaware of their deficit – inabilty to recognize non verbal sounds,preserved ability to comprehend speech , amusia a subtype – inablity to percieve music

29. ..take home message Neonatal screening should include BERA and not just OAE especially in high risk cases Always consider AN/AD as a DD for SNHL in children and adults especially those with speech recognition difficulties Clearer protocols to locate site of insult in AD/AN is lacking ,,, eg : no tests are available to asses the function of IHC Need protocols to describe - stable AN/AD -progressive AN/AD- manifests in adolescents or early childhood -reversible AN/AD -maturational defects Hearing aid or cochlear implant??