Characteristics and prognostic assessment of acute low-frequency sensorineural hearing loss: a retrospective analysis of 546 cases

Abstract

Background/Objectives

The incidence of acute low-frequency hearing loss has gradually increased in recent years. However, its specific etiology and pathophysiology remain largely unclear. Therefore, the aim of this study was to investigate the prognostic factors of acute low-frequency sensorineural hearing loss.

Patients and methods

Patients were grouped based on post-treatment pure-tone hearing thresholds: complete, marked, and slight recovery, or no change. We analyzed correlations between prognosis and age, sex, affected side, pathogenesis, underlying diseases, onset days, dizziness, degree of hearing loss, vestibular function, electrocochleography results, and gadolinium-enhanced inner ear MRI. Correlational analyses were completed using univariate and multivariate logistic regression. A p-value < 0.05 was considered statistically significant.

Results

Overall 546 patients with acute low-frequency sensorineural hearing loss were included. Univariate analysis revealed significant differences among groups regarding age, onset days, degree of hearing loss, cochlear hydrops on gadolinium-enhanced inner ear magnetic resonance imaging, and abnormal electrocochleography (all p < 0.001), and in caloric and head impulse test results (all p < 0.05). Multivariate logistic regression analysis showed that age, severe hearing loss, and abnormal electrocochleography results were significantly associated with prognosis. Age (p < 0.001) and electrocochleography results (p < 0.05) were significantly associated with complete recovery; degree of hearing loss was significantly associated with obvious effects (p < 0.01).

Conclusions

Advancing age, abnormal electrocochleography, and degree of hearing loss were independently associated with poor prognosis of ALHL . With further study, these results could drive the development of improved clinical diagnostic guidelines to ultimately impact patient outcomes.

KEY MESSAGES

1. This retrospective analysis of 546 cases elucidated the characteristics and prognostic assessment of acute low-frequency sensorineural hearing loss.

2. Results showed that age, onset, degree, hydrops, electrocochleography, and caloric/head impulse impact prognosis and that combining gadolinium-enhanced MRI and electrocochleography may be useful in complex cases.

3. Youth and normal electrocochleography were positive predictors for hearing recovery.

Introduction

Acute low-frequency sensorineural hearing loss (ALHL), first defined by Abe in 1982 [1], refers to hearing loss primarily due to low-frequency impairment with preserved medium and high-frequency hearing. Previously, ALHL was considered a distinct form of sudden sensorineural hearing loss characterized by a high cure rate, high recurrence rate, and clinical features that can progress to Meniere’s disease [2–4].

The etiology and pathophysiological mechanisms of ALHL remain unclear. The most widely recognized causes include endolymphatic hydrops and autoimmune reactions [5]. Electrocochleography and gadolinium-enhanced inner ear magnetic resonance imaging (MRI) can be performed to diagnose endolymphatic hydrops. A 3.0-T MRI with intravenous gadolinium contrast can directly visualize the location of hydrops [6]. Corticosteroid treatment is effective with a high cure rate; however, relapses are common, and the condition can progress to Meniere’s disease. In recent years, the incidence of ALHL has gradually increased. In addition, the early stages of Meniere’s disease present with clinical symptoms similar to those of ALHL, making differential diagnosis challenging. The pathogenesis and prognostic factors of ALHL have been investigated and analyzed; however, no authoritative clinical diagnostic or treatment guidelines have been established.

In this study, we summarized and analyzed factors associated with prognosis in patients with ALHL at initial onset, including age, sex, affected side, pathogenesis, underlying diseases, onset days, dizziness, degree of hearing loss, vestibular function, electrocochleography, and gadolinium-enhanced inner ear MRI (to determine the presence of cochlear and/or vestibular hydrops).

Patients/material and methods

Case data

A retrospective analysis was performed on adult patients with unilateral ALHL at our hospital between January 2018 and April 2023.

Inclusion criteria were as follows: (1) acute onset of sensorineural hearing loss within 72 h, with an average threshold (125, 250, 500 Hz) ≥ 30 decibels hearing level (dB HL) and a high-frequency average (2, 4, 8 kHz) ≤ 20 dB HL (Figure 1) [7]; (2) age between 18 and 70 years, with unilateral hearing loss; and (3) no previous history of dizziness, vertigo, migraine, or dizziness associated with hearing loss, tinnitus, or ear fullness during treatment.

Figure 1.

Audiometry of a 23-year-old male with a six-day sensorineural hearing loss in the right ear. The dotted line represents the air conduction hearing after treatment, and the solid line represents the air conduction hearing before treatment. dB, decibels; Hz, hertz.

Exclusion criteria were as follows: (1) middle ear disease, retrocochlear space-occupying lesions, Meniere’s disease, auditory neuropathy, and other diseases causing hearing loss; and (2) pregnant women and individuals with contraindications to corticosteroid use.

Procedures

Audiological examination

Before treatment, all patients underwent pure-tone threshold audiometry, acoustic immittance testing, distortion product otoacoustic emission testing, auditory brainstem response testing, and additional tests to exclude related lesions and determine the baseline hearing level. The treatment outcome was evaluated based on the results of pure-tone audiometry conducted 3 months after treatment.

Vestibular function examination

This examination included the caloric test (Ulmer VNG, v.1.4; SYNAPSYS, Marseille, France), vestibular evoked myogenic potential (VEMP) test (Neurosoft LTD, Ivanov, Russia), video head impulse test (HIT) (Ulmer, SYNAPSIS), and vestibular autorotation test (VAT) (Western Systems Research, Pasadena, CA, USA).

The degree of hearing loss and recovery or therapeutic effects refer to those included in the Chinese Guidelines for the Diagnosis and Treatment of Sudden Deafness (2015) [8]. Recovery (therapeutic effect) was classified as follows: (1) complete recovery, hearing thresholds at the affected frequencies returned to normal, matched those of the contralateral ear, or returned to pre-onset levels; (2) marked recovery, average hearing improved by >30 dB; (3) slight recovery, average hearing improved by 15–30 dB; and (4) no recovery, average hearing improvement was <15 dB.

Examination of hydrops in the membranous labyrinth

All patients were evaluated for endolymphatic hydrops using either gadolinium-enhanced inner ear MRI or electrocochleography (ECoG), based on their clinical status and willingness to undergo the examination. The electrocochleography (GSI Audera Auditory Evoked Potentiometer) showed a positive summating potential/action potential ratio > 0.4. An enhanced 3.0-T MRI of the inner ear was performed with an intravenous injection of the contrast agent gadolinium diammonium at a dose of 0.2 mL/kg. The scan was performed 6 h after the injection, and the report was issued by two senior radiologists. The results were classified as either normal MRI of the inner ear or cochlear and/or vestibular hydrops (Figure 2 shows an abnormal MRI in a patient with mild left ALHL and cochlear and vestibular hydrops).

Figure 2.

Delayed gadolinium-enhanced inner ear magnetic resonance image shows grade II cochlear and grade II vestibular hydrops in the left ear (red arrows).

Treatment methods

All patients received a standardized 7-day treatment course using the same medication regimen. The treatment methods aimed to improve blood circulation using medications, including Ginkgo biloba extract (87.5 mg/day, intravenous drip) and methylprednisolone sodium succinate (40 mg, intravenous drip once daily or postotic injection every other day).

Statistical analysis

Statistical analyses were performed using SPSS version 22 and R software version 4.3.2 (IBM, Armonk, NY, USA). Univariate and multivariate logistic regression analyses were used for correlation analysis. Univariate analyses were first performed to examine factors associated with the degree of hearing recovery. For categorical variables, differences among groups were assessed using the chi-square test. For continuous variables, one-way analysis of variance (ANOVA) was used for normally distributed variables, whereas the Kruskal–Wallis test was used for non-normally distributed variables. Variables that were statistically significant in the univariate analyses were subsequently included in a multivariable multinomial logistic regression model. Using the no recovery group as the reference category, the slight recovery, marked recovery, and complete recovery groups were compared with the reference group to identify factors independently associated with different levels of hearing recovery. A p value < 0.05 was considered statistically significant.

Ethical considerations

This research was conducted in accordance with the principles stated in the Declaration of Helsinki. The study design was approved by the Medical Ethics Committee of Shandong Provincial Second People’s Hospital (No. 2023-006-01). Written informed consent was obtained from all participants for study participation. Consent included participation in the research and approval of the publication of this article. Each patient provided consent for use of their images and/or information for the purpose of education and research.

Results

Clinical characteristics

A total of 546 patients with ALHL (mean age: 40.8 ± 12.7 years) were enrolled. The male-to-female ratio was 0.51:1, the left-to-right affected-side ratio was 1.45:1, and the median disease duration was 12.0 (Q1, Q3: 5.0, 24.75). Triggering factors were identified in 228 patients, including sleep disorders, mood swings, alcohol consumption, respiratory tract infections, fatigue, and noise exposure. A total of 93 patients had underlying diseases, including hypertension, diabetes, coronary heart disease, and hyperlipidemia, with some patients having multiple conditions. Dizziness was reported in 253 patients.

Degree of hearing loss and therapeutic grouping

Mild, moderate, and severe hearing loss were observed in 311, 224, and 11 patients, respectively. Owing to the small number of severe cases, moderate and severe hearing loss were combined in the statistical analysis and referred to as the moderate–severe group. Patients were categorized into four treatment outcome groups: complete recovery group (n = 276), marked recovery group (n = 35), slight recovery group (n = 84), and no change group (n = 151). The distribution of mild to moderate–severe hearing impairment is shown in Table 1. Univariate analysis revealed statistically significant differences in hearing prognosis (p < 0.001).

Table 1.

Univariate analysis of hearing outcomes by clinical features.

Variables		Auditory efficacy				p-Value
		no change	slight recovery	marked recovery	complete recovery
Age* (y, M (Q1, Q3))		44.0 (34.5, 52.0)	38.0 (32.0, 52.0)	46.0 (39.0, 53.0)	35.5 (30.0, 45.0)	<0.001
Sex	Male	59	32	13	81	.159
	Female	92	52	22	195
Side	Left	91	56	20	156	.409
	Right	60	28	15	120
Onset days *(d, M (Q1, Q3))		20.0 (13.5, 36.0)	15.0 (7.0, 30.0)	13.0 (5.5, 22.0)	6.0 (3.0, 15.0)	<0.001
Inducement	Yes	51	37	14	113	.410
Underlying diseases	Yes	31	13	9	40	.275
Dizziness	Yes	61	39	16	137	.340
Degree of hearing loss*	Mild	83	34	6	188	<0.001
	Moderate severe	68	50	29	88
Gadolinium MRI cochlea*	EH	45	19	17	39	<0.001
Gadolinium MRI vestibule	EH	32	18	9	57	.946
Electrocochleography*	Positive	19	4	7	14	<0.001
Caloric test*	Abnormal	85	39	22	121	.016
cVEMP	Unilateral Abnormal	49	28	8	82	.345
	Bilateral Abnormal	33	18	6	35
oVEMP	Unilateral Abnormal	38	28	9	71	.213
	Bilateral Abnormal	40	22	8	41
HIT*	Unilateral Abnormal	18	6	4	11	.007
	Bilateral Abnormal	10	4	5	9
VAT	Abnormal	38	56	22	132	.901

*p < 0.05; M, median; IQR, interquartile range; MRI, magnetic resonance imaging; EH, endolymphatic hydrops; cVEMP, cervical vestibular evoked myogenic potential; oVEMP, ocular vestibular evoked myogenic potential; HIT, head impulse test; VAT, vestibular autorotation test.

Vestibular function examination

All patients underwent routine vestibular function testing, including bithermal caloric testing and the head impulse test (HIT); however, some patients did not complete these tests because of refusal or inability to cooperate. Bithermal caloric testing was completed in 526 patients, whereas 20 patients did not complete the test. The HIT was completed in 459 patients, whereas 87 patients did not complete the test. A univariate correlation analysis was conducted to examine the association between vestibular function and hearing loss outcomes. Among the vestibular tests, only abnormalities detected in the caloric test and HIT were significantly correlated with different hearing outcome grades (all p < 0.05; Table 1).

Endolymphatic hydrops

Univariate analysis of hearing outcomes, positive electrocochleography results, and gadolinium-enhanced inner ear MRI showed a significant correlation with cochlear hydrops (all p < 0.001).

Correlation analysis of hearing efficacy

Univariate analysis showed that age, onset days, degree of hearing loss, cochlear hydrops revealed by gadolinium-enhanced inner ear MRI, abnormal electrocochleography, abnormal caloric test, and abnormal HIT were statistically significantly different across the four therapeutic groups (all p < 0.05), as shown in Table 1. Multivariate logistic regression analysis showed that age, severe hearing loss, and abnormal electrocochleography were significantly correlated with an ineffective prognosis. Age (p < 0.001) and electrocochleography results (p < 0.05) were significantly associated with the prognosis of hearing recovery, and the degree of hearing loss was associated with the obvious effect (p < 0.01), as shown in Table 2. Due to the limited sample size, the cell counts in the cross-tabulation of cochlear hydrops on gadolinium-enhanced inner ear MRI and electrocochleography results were too low, resulting in complete separation during the interaction analysis. To maintain the stability of the statistical model, the interaction term was therefore excluded from the model.

Table 2.

Multivariate logistic regression analysis of hearing outcomes.

Variables	Slight recovery group		Marked recovery group		Complete recovery group
	p-Value	OR (95% CI)	p-Value	OR (95% CI)	p-Value	OR (95% CI)
Age	0.024	0.96 (0.93–1.00)	0.067	0.96 (0.92–1.00)	<0.001	0.94 (0.91–0.97)
Initial (reference: mild)
Moderate severe	0.086	2.00 (0.91–4.43)	0.003	10.60 (2.19–51.36)	0.889	1.05 (0.52–2.11)
Electrocochleography (reference: normal)
Positive	0.040	0.28 (0.08–0.94)	0.760	1.22 (0.34–4.40)	0.023	0.33 (0.13–0.86)
Constant	0.182		0.833		<0.001

The three therapeutic groups were compared with the group with no final therapeutic effect. OR, odds ratio; CI, confidence interval. Statistical significance considered at p < 0.05.

Discussion

ALHL is a distinct subtype of sudden sensorineural hearing loss. The primary symptoms include tinnitus, a sensation of ear fullness, and heightened self-hearing, with or without dizziness. Compared with other types of sudden deafness, its short-term prognosis is favorable; however, hearing loss may recur [9]. Most studies of ALHL have reported post-treatment hearing recoveries in approximately 80% of the affected ears [10,11]. Some researchers/clinicians consider ALHL to be the early stage of Meniere’s disease. Hearing recovery in ALHL is superior to that in Meniere’s disease (67.7% vs. 54.5%) [12]. ALHL tends to resolve spontaneously, with 50%–70% of untreated patients experiencing recovery [10]. Many patients who undergo short-term treatment experience the return of normal hearing. However, approximately one-third of patients do not fully recover within a short period of treatment [13]. Therefore, we aimed to explore the factors influencing the prognosis of ALHL.

The pathogenesis of sudden hearing loss in ALHL remains unclear; however, widely recognized mechanisms include inner ear vascular spasm, stria vascularis dysfunction, vascular embolism or thrombosis, hydrops of the membranous labyrinth, and hair cell injury. Among these, the low-frequency hearing loss is primarily attributed to hydrops of the membranous labyrinth [11]. Numerous factors influence the prognosis of sudden sensorineural hearing loss. According to previous studies, the prognostic factors in patients with sudden sensorineural hearing loss include onset days, vertigo and tinnitus, type of hearing loss, and degree of early hearing loss [14].

The present study involved a retrospective analysis of factors that may influence the prognosis of ALHL. The clinical data of 546 patients with ALHL were analyzed to assess the effects of age, sex, affected side, pathogenesis, underlying disease, dizziness, degree of hearing loss, onset days, hydrops (evaluated via gadolinium-enhanced inner ear MRI and electrocochleography), and vestibular function on hearing prognosis. Additionally, gadolinium-enhanced inner ear MRI results were further classified into cochlear and vestibular hydrops. Vestibular functional subdivisions and the effect of unilateral or bilateral abnormalities on hearing outcomes were also examined. A univariate analysis was performed for these outcome groups. The results showed that age, onset days, degree of hearing loss, cochlear hydrops detected by gadolinium-enhanced inner ear MRI, and abnormal electrocochleography, caloric test, and HIT were significantly associated with the therapeutic outcome groups (all p < 0.05). A study by Shin et al. also reported that youth, mild hearing loss, early treatment, and female sex are favorable prognostic factors [15]. Additionally, Sato et al. identified female sex as a unique predictor of favorable prognosis in ALHL [16]. In the present study, the proportion of women in each treatment outcome group was higher than that of men. Diao T et al. also reported a higher prevalence of ALHL among female patients [17]; however, the difference was not statistically significant .This may have been due to the relatively small sample size or the age distribution within the inclusion criteria.

Previous studies have identified dizziness as a factor associated with poor prognosis in ALHL [9]. However, no statistically significant difference was observed for this factor in the univariate analysis of hearing outcomes in the present study. In the vestibular function assessments, abnormal results in both the caloric test and HIT were significantly correlated. Upon refining the results of the vestibular function tests, we found that functional abnormalities could occur in both the affected and contralateral ears. As discussed previously in the text, ALHL may be associated with an autoimmune reaction in the inner ear. Song et al. explained the pathogenesis of common vestibular diseases from an immunological perspective, suggesting that immune responses can alter vestibular function, leading to both hearing and balance disorders [18]. Therefore, when the body mounts an immune response, the function of the affected ear may be impaired, and in severe cases, both ears may be affected. Vestibular dysfunction may also be present in individuals without dizziness symptoms. Clinically, attention should be given to vestibular function, particularly via caloric testing and HIT, to ensure appropriate treatment and rehabilitation measures.

Previous studies have shown a potential correlation between ALHL and hydrops of the membranous labyrinth, suggesting that ALHL may be related to endolymphatic edema caused by an autoimmune reaction in the endolymphatic sac [19,20]. Studies by Seo et al. and Shimono et al. found that cochlear hydrops on the affected side of ALHL were significantly more prevalent than those on the opposite side. Their studies found no statistically significant difference between the incidence of vestibular hydrops and its contralateral ratio, indicating that cochlear hydrops play a role in the pathogenesis of ALHL [5,21]. Electrocochleography and gadolinium-enhanced inner ear MRI are commonly used methods to detect inner ear hydrops, offering ease of use. For patients who are claustrophobic, allergic to contrast media, or have metal implants, electrocochleography can detect inner ear hydrops, provided the eardrum is intact without perforations, congestion, or thinning. However, false negatives can occur with electrocochleography. Compared with electrocochleography, gadolinium-enhanced inner ear MRI is more accurate, more sensitive, and can locate and grade inner ear fluid (cochlear and/or vestibular). To improve the detection rate of hydrops in the membranous labyrinth and confirm their presence in the cochlea and/or vestibule, we combined electrocochleography with intravenous gadolinium MRI to detect inner ear hydrops. Our results showed that prognosis was significantly associated with positive electrocochleography results, a finding confirmed by Jiang et al. and Inui et al. [13,22]. Patients with cochlear fluid (with or without vestibular fluid) had poorer hearing recovery. Multivariate analysis of different prognostic categories showed that age, severe hearing loss, and abnormal electrocochleography were significantly associated with prognosis, whereas youth and normal electrocochleography were positive predictors for recovery. In actual clinical applications, the cost of MRI examinations and limited equipment availability must also be considered. Nevertheless, in some complex or poorly prognosed cases, clinicians could consider combining cochlear electrocochleography and gadolinium-enhanced inner ear MRI to assess patient prognosis.

The strengths of this study lie in the broad range of variables that were considered and investigated. Furthermore, the study categorized endolymphatic hydrops into cochlear and/or vestibular hydrops. Analyses also detailed the vestibular function and the impact of unilateral or bilateral abnormalities on hearing, which hold significant guidance value for future clinical work. However, this study had some limitations. The study was retrospective, and potential bias may have occurred. The primary efficacy outcome of this study was assessed at 3 months after treatment and therefore mainly reflected short-term hearing recovery rather than long-term prognosis. Acute low-tone hearing loss (ALHL) is characterized by fluctuating hearing loss and recurrence, and some patients may further progress to subsequently develop Ménière’s disease. Therefore, the 3-month follow-up in this study cannot fully reflect the long-term outcomes of the disease. Future longitudinal studies with longer follow-up are warranted to clarify the natural history, recurrence patterns, and risk of progression to Ménière’s disease. The single-center design and the relatively small sample size of the severe cases may limit generalizability. Future prospective studies with larger sample sizes are needed to further validate these results.

Conclusions

Overall, univariate analysis in the present study identified age, disease duration, degree of hearing loss, cochlear hydrops on gadolinium‑enhanced inner‑ear MRI, abnormal electrocochleography, abnormal bithermal caloric test, and abnormal head‑impulse test as potential prognostic factors for ALHL. However, subsequent multivariate logistic regression analysis demonstrated that only advancing age, abnormal electrocochleography, and degree of hearing loss were independently associated with poor prognosis in patients with ALHL.With further study, these findings may inform clinical decision making in the diagnosis and management of patients with ALHL.

Funding Statement

This work was supported by the Shandong Provincial Natural Science Foundation under Grant number ZR2023MH287.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The data that support the findings of this study are available from the corresponding author [MW] upon reasonable request.