In the present study, non-invasive testing procedures were used.All the conditions complied with the declaration of Helsinki. All the test procedures were explained to the family members before testing and informed consent has been taken from the parents.

Results

  The data collection was done in three visits of the infant to the rehabilitation center in Mumbai and findings are given accordingly,

Visit 1: The infant was 3-month-old. He was taken up for behavioral observation audiometry. He was awake and calmly seated on the mother's lap wearing the headphones.The clinician observed response to 45 dB SPL in both ears for warble tone delivered through TDH-39 headphones (Telephonics, 815 Broad Hollow Road, Farmingdale, NY) housed in MX-41AR cushion.The responses observed were eye-widening and eye movements in search of the sound source.However, an inverted ‘L’ Jerger pattern was observed on acoustic reflexes for 1 kHz tone with absent ipsilateral and contralateral reflexes in the left ear.This was observed despite the ‘A’ type tympanogram and healthy tympanic membrane on Otoscopic evaluation in both the ears.Absent acoustic reflexes with the presence of behavioral responses to sound warranted further physiological evaluations.

  The presence of otoacoustic emissions in both the ear and the absence of ABR in the left ear at both levels cleared the diagnostic picture.Also, prolonged Cochlear Microphonics was observed at moderate to higher presentation levels in the left ear ABR recordings (Figure 3), stimulus artifacts were ruled out by pitching the tube of the transducer.The child was diagnosed with unilateral auditory neuropathy secondary to TBI.Additionally, the absence of left contralateral reflexes was suggestive of mild retrocochlear pathology on the right side. The speech and language evaluations revealed a delay of 3 months in receptive and expressive language on the Receptive-Expressive Emergent Language test (REEL).The parents were counseled about regular monthly follow-up and speech and language stimulation therapy at the center.

Visit 2:In the second session, after two months, it was observed that the ipsilateral reflexes were present in both ears.However, contralateral reflexes remained absent.Similarly, ABR screening revealed pass in the left ear at 60 dB nHL and fail at 35 dB nHL. Rest all the test findings remained unchanged on the second visit.Parents were asked to continue speech therapy and follow up in the next month for audiological evaluations.

Visit 3: The child has completed seven months of age and the mother reported that the child has started to smile when spoken to and tracks the speaker.On repeating detailed audiological evaluation it was found that the entire test findings came within normal limits.Along with, diagnostic ABR evaluation demonstrated the presence of wave V till 10 dB nHL in both ears (Figure 4).During these visits, the child was attending speech therapy and physiotherapy (neurodevelopmental therapy) once a week at the clinic and was on medications given by the neurologist.

Discussion

  The absence of ABR in the left ear can be attributed to the bilateral diffuse cortical gliosis as reported in the MRI (Figure 1 and 2).The recovery observed in six months from the trauma can be attributed to two components; first, the activity-dependent neuroplasticity, as summarized by Ganguly and Poo[22] a specific task-oriented behavior could redistribute the cortical nerve allocation.This could be due to regular auditory input facilitated by intense language stimulation.The observation made by Scheibel, Newsome[23] seconds the above finding, reporting over activation of the brain to partially improve cognitive functioning.Secondly, the spontaneous drainage of neurotoxic subdural accumulation in the brain added to the recovery.Psarommatis, Riga[21] tested 177 neonates and reported spontaneous recovery of auditory neuropathy in 13 out of 20 infants on follow-up.They concluded that one should wait for six months before making any amplification decisions in the clinics based on the high-risk register and clinical findings.

  Dewan, Rattani[2] found that reactive astrocytes can increase excitatory synaptic strength.Other authors have also found that reactive astrocytes maintain the homeostatic synaptic plasticity required to obtain effective brain circuit functioning.This modulation in the firing of neurons was reported to be regulated by the production of α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptor and cytokine TNFα[24,25].It was also explained by Burda, Bernstein[26] that Astrocytes are responsible for post-traumatic tissue repair and demonstrate good potential in speeding recovery.

Conclusion

  The present study reported the audiological profile of a child who acquired auditory dyssynchrony after TBI.The child also presented with marked damage in the functioning of the visual nerve and hemiparesis on the right side as diagnosed by the respective members of the medical team.The subsequent follow-up revealed complete audiological recovery from auditory dyssynchrony pattern.Hence, the current study supports the inference drawn by Psarommatis, Riga[21] to rest the intervention till the child diagnosed with ANSD, who otherwise demonstrates normal hearing unilaterally on the behavioral and electrophysiological auditory test, attains six months of age.

  The parents were asked to follow up once in three months for regular audiological and speech and language developmental screening.Further research is required to support the probable cause of the recovery.The limitation of the current study is that child’s hearing evaluations were not done before the traumatic injury and hence the presence of congenital auditory spectrum disorder cannot be ruled out.However, the unilateral paresis was not present since birth and was reported after the trauma.

Acknowledgements

  The authors would like to thank the parents of the infant for their co-operation.

Funding

  No funding sources.

Conflict of Interest

  The author declares no conflict of interest in the present study.

Ethical Approval

  Not required.