Table 1

Characteristics and findings of the eligible studies that performed vestibular-specific assessments

First author, year, country	Study design	N	N with hearing loss (HL)*	Age (mean)†	Mode of vestibular assessment	STROBE quality	Vision assessment	Findings
Bernard, 2015, France20	R Cohort	22 ScCMV 30 AcCMV	48 (18 ears with MI/MO HL; 68 ears with SE/PR) CI use not reported	34.7 months	Caloric EVAR HIT OVAR CVEMP	Low	Not assessed	90.4% (47) had canal dysfunction (caloric, EVAR, HIT) and 86.5% had otolith dysfunction (OVAR, cVEMP). 30.8% (16) had bilateral areflexia (lack of response) to all tests, 40.4% (21) had partial bilateral dysfunction and 21.1% (11) had unilateral dysfunction. 50% (7 out of 14) had progressive deterioration in vestibular function a mean follow-up period of 26.3 months.
Dhondt, 2019, Belgium23	Case Series	4 ScCMV 1 AcCMV	5 SE/PR (3 using CI)	2–7.3 years	vHIT Rotatory test Caloric CVEMP OVEMP	Low	Not assessed	80% (4) had peripheral vestibular dysfunction (2 unilateral, 2 bilateral) 2 had vestibular deficit established before cochlear implant surgery Vestibular function can fluctuate; vestibular symptoms are episodic.
Dhondt, 2021, Belgium19	P Cohort	41 ScCMV 52 AcCMV	3 AcCMV (1 MO, 2 SE/PR) 14 ScCMV (1 MO, 13 SE/PR) ≥3 using CI	7.2 months	vHIT Rotatory Test cVEMP	Moderate-low	Funduscopy	22% (9) ScCMV and 8% (4) AcCMV had vestibular loss (7 unilateral, 6 bilateral) 10% (6 out of 61) had deterioration in vestibular function over mean follow-up period of 10.2 months. 3.8% (2) AcCMV and 2.3% (1) ScCMV had abnormal funduscopy.
Inoue, 2013, Japan17	P Cohort	8 cCMV	8 PR (pre-CI)	38 months	Damped Rotatory test Caloric cVEMP	Moderate-low	Not assessed	40% (2 out of 5) had abnormal rotation test (1 unilateral, 1 bilateral). 33% (2 out of 6) had abnormal caloric response (1 unilateral, 1 bilateral). 67% (4 out of 6) had abnormal VEMP response (1 unilateral, 3 bilateral). 13% (1) had delayed head control and 25% (2) had delayed independent walking.
Karltorp, 2014, Sweden22	Case–control	6 ScCMV 20 AcCMV 13 Controls (Cx26)	26 SE (post-CI) cCMV 13 SE (post-CI) controls	7.8 years	Movement ABC-2 Caloric vHIT cVEMP	Moderate-Low	Visual acuity Ocular alignment Funduscopy	88% (23 out of 26) had balance disturbance. 90% (9 out of 10) had abnormal caloric response (five unilateral, 4 bilateral). 20% (5) had unilateral ocular pathology (mainly chorioretinal scars).
Laccourreye, 2015, France18	R Cohort	15 cCMV	15 PR (pre-CI)	14–36 months	Caloric	Moderate-low	Investigation not specified	80% (12) had areflexia (4 unilateral, 8 bilateral). 20% (3) had ophthalmic abnormality. No further details reported.
Maes, 2017, Belgium21	Cross-sectional	16 ScCMV 8 AcCMV 8 cCMV negative controls 8 Cx26	8 ScCMV (R ear 80 dB SD 27; L ear 68.8 SD 39.3)* 0 using CI	6.7 months	cVEMP	Moderate	Visual-motor integration (Peasbody Developmental Motor Scale)	57% (4 out of 7) ScCMV with HL had no cVEMP response (1 unilateral, 3 bilateral). 14% (1 out of 7) ScCMV with NH had no cVEMP response (1 unilateral). 100% (8) AcCMV had normal cVEMP response. ScCMV with HL had significantly gross lower motor scores compared with all other groups.
Pappas, 1983, USA24	Case–control	19 AcCMV 17 cCMV negative controls	14 (1 MI, 1 MO, 12 SE/PR) CI use not reported	41 months	Caloric	Moderate–low	Not assessed	80% (4 out of 5) AcCMV with normal hearing had hypoactive/absent caloric responses (3× unilateral, 1× bilateral). 50% (3 out of 6) AcCMV with HL had hypoactive/absent caloric responses (1× unilateral, 2× bilateral). 8 patients could not have vestibular function confirmed.
Paul, 2017, France16	R Cohort	3 ScCMV 5 AcCMV	8 (2 MO, 6 PR/total HL) CI use not reported	18 months	Canal and otolithic tests	Moderate-low	Not reported	25% (2) had vestibular dysfunction. Ophthalmological examination findings not reported. No further details available.
Pinninti, 2021, USA11	Case–control	40 AcCMV 33 cCMV negative controls	7 (2 MI, 2 MO/SE, 2 PR, 1 not reported) CI use not reported	7.52 years	Rotatory test SVV cDVA cVEMP SOT BOT-2	Moderate	Vestibulo-visual tract Gaze stability	44.8% (13/29) had low VOR on rotatory chair testing. 44.7% (17 out of 38) had a diminished or absent cVEMP response (10 unilateral, 7 bilateral). 48.7% (19 out of 39) had difficulty maintaining stable vision during head movement. Up to 50% had difficulties maintaining balance.
Strauss, 1985, USA9	P Cohort	6 ScCMV 5 AcCMV	3 ScCMV (SE) CI use not reported	22 months–8.5 years	Caloric	Low	Not assessed	50% (3) ScCMV normal neurodevelopment. 50% (3) ScCMV with HL had abnormal vestibular responses to caloric test (2 unilateral, 1 bilateral).
Zagólski 2007, Poland10	Case–control	10 ScCMV 16 AcCMV 40 cCMV negative controls	8 ScCMV ears (SE/PR) CI use not reported	3 months	Caloric cVEMP	Moderate	Not assessed	60% (12/20) ScCMV ears had no cVEMP response. 12.5% (4/32) AcCMV ears had absent caloric response. 60% (12/20) ScCMV ears had absent caloric response. No pathological finding on clinical examination.

Study design: R=retrospective; P=prospective.
Hearing loss=severity reported where available.
For mode of vestibular assessment, please see appendix A for glossary of vestibular and balance investigations.
Findings: (n)=number of cCMV cases out of N, where number of children tested is different to N, (n out of….) is reported.
*Where only mean decibel (dB) hearing threshold was reported, this can be interpreted as: <20 dB=normal; 21–40 dB=mild; 41–70 dB=moderate; 71–90 dB=severe; 91–119 dB=profound (Bernard, 2015).
†Range (where mean not reported).
ABC, assessment battery for children; AcCMV, asymptomatic cCMV; BOT-2, bruininks-oseretsky test of motor proficiency, second edition (BOT-2); cDVA, clinical dynamic visual acuity; CI, cochlear implant; cVEMP, cervical vestibular myogenic evoked potential; Cx26, connexin 26 mutation; EVAR, earth vertical axis rotation; HL, hearing loss; MI, mild; MO, moderate; N, number of cCMV cases; NH, normal hearing; OVAR, off vertical axis rotation; oVEMP, ocular vestibular myogenic evoked potential; P, prospective; PR, profound; R, retrospective; ScCMV, symptomatic CMV; SE, severe; SOT, sensory organisation test; SVV, subjective visual vertical; vHIT, video head impulse testing ; VOR, vestibulo-ocular reflex.