A detailed audio-vestibular profiling was performed to assess the status of outer, middle, and inner ear. The audio-vestibular test battery comprised of Pure tone audiometry, speech audiometry, tympanometry, acoustic reflexometry, otoacoustic emissions (OAEs), auditory brainstem response (ABR), and vestibular tests (ocular VEMP (oVEMP), cervical (cVEMP), and vestibulogram).

Immittance audiometry

A calibrated immittance equipment (Inventis Clarinet, Inventis Inc., Padova, Italy) was used to evaluate the middle ear functioning. Tympanometry was done bilaterally using a probe tone of 226 Hz. Ipsilateral and contralateral acoustic reflex threshold measurement at 0.5, 1, 2, and 4 kHz was carried out in both the ears. The results revealed ‘As’ type tympanogram [9] with absent acoustic reflexes bilaterally with tympanometric peak pressure of 11 and – 3 daPa, static admittance of 0.30 and 0.31 mmho, ear canal volume of 0.66 and 0.71 cm3 in right and left ear, respectively. This indicated a possible middle ear pathology in both ears.

Pure tone and speech audiometry

Pure tone and speech audiometry were performed in a sound treated room with ambient noise level in adherence to ANSI S3.6-2018. Pure tone threshold, Speech detection/recognition threshold, speech identification score, speech perception in noise and uncomfortable loudness level were estimated using a calibrated audiometer, Inventis Piano (Inventis Inc., Padova, Italy). Air conduction and bone conduction thresholds were determined with Telephonics dynamic supra-aural Headphones-49 (Telephonics, Farmingdale, NY, USA) and Radioear B-71 bone vibrator (RadioEar New Eagle, PA, USA) respectively. The AC and BC thresholds were tracked using modified Hughson-Westlake method [10] at octave frequencies from 0.25 to 8 kHz and 0.25 to 4 kHz respectively. Pure tone thresholds indicated a 4 frequency pure tone averages (0.5, 1, 2, 4 kHz) being 91.25 and 33.75 dB HL in the right and left ear respectively. The degree of hearing loss was inferred from the average of hearing thresholds at 0.5, 1, 2, and 4 kHz and interpreted using Clark classification [11]. The air and bone conduction thresholds across octave frequencies is shown in Fig. 1. Based on the audiometry, child was diagnosed as profound mixed hearing loss in the right ear and mild mixed hearing loss in the left ear. Conductive component seen in both ears in the child can point to unresolved middle ear issues, which were reported at the age of 5 years (discussed in the case history).

Fig. 1
figure 1

Auditory thresholds corresponding to the right ear (A) and left ear (B) in the test of pure tone audiometry

Speech audiometry was carried out using Malayalam wordlist (Spondee wordlist and PB word list) and speech reception threshold (SRT) in the left ear was found to be 40 dB HL. Speech Identification Score (SIS) was found to be 100% in the left ear. Speech perception in noise (SPIN) scores were 68% at 0 dB SNR and 72% at 5 dB SNR in the left ear. Speech detection threshold (SDT) in the right ear was found to be 90 dB HL.

Otoacoustic emissions (OAEs)

Transient evoked otoacoustic emissions (TEOAEs) and Distortion product otoacoustic emissions (DPOAEs) were recorded using Otodynamics ILO V6 DP Echoport (Otodynamics Ltd., Hatfield, Herts, England). TEOAEs were recorded for each ear separately for non-linear click trains presented at 80 dB peak equivalent SPL. On other hand, DPOAE was done across the frequency band of 1000 Hz to 6000 Hz with F2:F1 ratio being 1.22:1 and constant stimulus intensity level of L1 = 65 dB SPL and L2 = 55 dB SPL. For TEOAE’s/DPOAE’s to be considered as present, a signal-to-noise ratio of at least 6 dB at 3 adjacent frequencies with wave reproducibility of > 80% is required. Both TEOAEs and DPOAEs were absent bilaterally across all the frequencies, suggestive of bilateral outer hair cell dysfunction.

Auditory brainstem response (ABR)

Natus Biologic Navigator pro (Natus Medical Incorporated, San Carlos, CA, USA) Auditory Evoked Potentials (AEP) system using Eartone 3A insert phones (Etymotic Research, Elk Grove Village, IL, USA; electrode impedance < 5000 Ω) was used to perform ABR testing. ABR threshold estimation using click stimuli in rarefaction polarity at 11.1 s−1 stimulus rate with 90 dB nHL as the starting intensity level was carried out for threshold estimation. ABR site of lesion was done at 11.1 s−1 and 90.1 s−1 stimulus repetition rate. High pass filter setting of 30 Hz and low pass filter setting of 1500 Hz was preset. To avoid electrical artifacts, a notch filter was kept at 50 Hz. For click evoked ABR, analysis window of 10.1 ms was used. To account for the replicability, at least two recordings of the waveform were recorded.

Waveforms were not traceable in the right ear, indicating severe to profound hearing loss. Waves could be traced up to 50 dB nHL in the left ear indicating mild hearing loss. Absolute latencies of wave I, III, and V were determined in the left ear. At 90 dB nHL, the peak latencies of I, III and V peaks were found to be 1.35, 3.76, and 5.35 ms respectively. The ABR waveforms of both ears are shown in Fig. 2 for the left ear (blue tracings) and right ear (red tracing) respectively, indicative of mild hearing loss in the left ear and severe-profound hearing loss in right ear.

Fig. 2
figure 2

Click evoked auditory brainstem response waveforms of the A left ear (in blue) and B right ear (in red)

Vestibular assessment

Behavioral vestibular tests which included Romberg test, sensitive Romberg test, Fukuda stepping test, Finger to nose test, Diadochokinetic test, bedside head impulse test, head shake nystagmus, and skew deviation were performed [12]. The child could maintain the posture up to 30 s in Romberg test and up to 11 s in sensitive Romberg test. Around 10° angle of deviation with less than 1 m of displacement in forward direction was observed in Fukuda stepping test. No tremors were seen in finger to nose test. The child was able to perform alternate task in DDK test. No nystagmus, saccades and skew deviations were noted.

Objective vestibular tests, cVEMP, and oVEMP were performed with the instrument Neurosoft-Audio (Neurosoft, Ivanovo, Russia) as the child failed in the behavioral vestibular tests and the no responses were noted in both the ears for both cVEMP and oVEMP. The test outcome were suggestive of bilateral sacculo-collic and utriculo-ocular pathway dysfunction.

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