Keywords
hearing loss - idiopathic sudden sensorineural hearing loss - metabolic syndrome -
hearing recovery
Introduction
Idiopathic sudden sensorineural hearing loss (ISSHL) is defined as an otologic urgency
with a rapid onset of hearing loss, of at least 30 dB (dB) in 3 or more consecutive
frequencies over 72 hours, disturbing 1 or both ears.[1] The incidence varies between 5 to 30 cases per 100 thousand patients/year.[1]
[2] The vast majority of cases (90%) are idiopathic, without a known etiology, despite
adequate investigation.[1]
[2]
[3] Classically, the most debated causes for this pathology are viral infection[2]
[4] and vascular disorders,[2] such as circulatory disturbance in the area of the anterior inferior cerebellar
artery related to special cochlear vulnerability, vestibular schwannoma, and perilymphatic
fistula.[1]
[2]
[3] Only in the last few years, the link between cardiovascular factors and ISSHL started
to be evaluated, and disorders such as diabetes mellitus (DM), arterial hypertension
(AHT), hyperlipidemia (HYL), ischemic heart disease, and obesity have been shown to
play an important role.[1]
[2]
[5] On the other hand, ISSHL was regarded as a possible sign preceding the development
of ischemic stroke.[5]
[6]
[7] Despite this evidence, it is still controversial if the occurrence of ISSHL and
its recovery should be considered cardiovascular risk biomarkers. The knowledge of
this association would be important for the treatment of ISSHL and to address these
cardiovascular preconditions in ISSHL patients.
In the last decades, a trend towards a change in the metabolic patterns of society
has been well recognized, with metabolic syndrome (MetS) being an increasingly common
condition.[8]
[9]
[10] In 2015, the reported prevalence in Europe was of 24%,[8] with a higher prevalence among women and with an age-associated prevalence increase
in all published cohorts.[8]
[9]
[10] Even more concerning is that this trend is also observed in younger populations,
who present higher obesity rates that necessarily increase the odds of developing
MetS.[8]
[9] Moreover, MetS is a risk factor for stroke, cardiac infarction, and cardiovascular-related
mortality.[8]
[9]
[10] Despite these associations, there are limited studies addressing the impact of MetS
on the level of recovery from ISSHL. Therefore, the present work aims to clarify whether
MetS affects the posttreatment outcomes of ISSHL.
Material and Methods
We designed a retrospective cohort study composed of ISSHL patients admitted for treatment
to a tertiary university hospital from January 2015 to December 2019. The hospital's
ethics committee approved the study, which was conducted from July to November 2020.
Included Patients and ISSHL Treatment Protocol
Initially, 104 consecutive patient records were analyzed, and, after applying the
inclusion/exclusion criteria, a final sample of 81 ISSHL patients were obtained. All
of the patients visited our Otorhinolaryngology Urgency Department and presenting
unilateral ISSHL that developed within 72 hours, with, at least, reduction of 30 dB
at 3 or more consecutive frequencies. Upon admission, all patients were diagnosed
through pure-tone audiometry (at least with assessments of the frequencies of 0.5 kHz,
1 kHz, 2 kHz and 4 kHz) and tympanometry to exclude other middle-ear conditions. Moreover,
we performed: a routine ear, nose, and throat (ENT) examination; collection of a blood
sample for the analysis of the hemogram of the the hepatic and renal functions; a
lipidic panel, including total, high-density lipoprotein (HDL), and low-density lipoprotein
(LDL) lipoprotein cholesterol, as well as triglycerides (TG); glucose screening with
C-reactive protein; an autoimmunity panel (for antinuclear antibodies [ANA], antineutrophil
cytoplasmic antibodies [ANCA], and antibodies to the inner ear antigen [anti-68kD]);
and an infectious panel (for syphilis, lyme disease, herpes I and zoster, Epstein-Barr
virus, toxoplasmosis, and rubella). It is within our protocol to propose to patients
their hospitalization for complete intravenous (IV) treatment for five days, to undergo
magnetic resonance scan, to exclude stroke and vestibular schwannoma or other cerebellopontine
angle conditions, and, finally, to undergo audiometric evaluations on the third and
fifth (last) days of the IV treatment to monitor their recovery progress. The daily
treatment includes the IV administration of 5 mg of dexamethasone twice a day, the
oral administrations of 5 mg of diazepam and 40 mg of pantoprazole, and insulin when
serum glucose is ≥ 160 mg/dL. The following rescue treatments were offered to all
patients, after informed consent, at the third or last days of hospitalization, in
case of absence of audiometric recovery or of recovery below 50%: 1) intratympanic
(ITY) dexamethasone (4 mg/mL) injection on a weekly basis (maximum of 3 injections),
completed after patient discharge; and 2) hyperbaric oxygen (HBO), planed on the fifth/last
day of the IV treatment. In regular conditions, HBO was started during the second
week of treatment, and it was administered for 20 sessions in an HBO center located
60 km from our medical center. It was possible to simultaneously propose HBO and ITY
dexamethasone. After hospital discharge, all patients were prescribed a slow tapering
of corticosteroid with prednisolone for 15 days. They were followed up weekly on the
first month for audiometric surveillance and, if necessary, repeated ITY dexamethasone.
After that, we requested a monthly visit until the sixth month, and the following
visits were under appointment or patient request, with at least one yearly visit.
The exclusion criteria were age under 18 years, history of head or acoustic trauma,
Ménière disease, exposure to ototoxic agents (such as aminoglycosides), more than
three days of delay following the onset of symptoms to start the treatment protocol,
ipsilateral otologic history (surgical or non-surgical), diagnosis of stroke or vestibular
schwannoma after imaging, evidence of infectious disease, and patient refusal to enroll
in the protocol. From an initial sample of 104 patients, 10 were excluded due to viral
infection (all of the cases caused by varicella zoster, diagnosed after blood sample
analysis according to the protocol), 4, due to anterior inferior cerebellar artery
(AICA)/cerebellum stroke, 4, due to posthead trauma hearing loss, 3, due to vestibular
schwannoma, 1, due to age > 18 years, and 1, due to refusal to enroll in the protocol.
Audiometric Assessment and Hearing Recovery Criteria
All patients underwent pure-tone average (PTA) audiometry and acoustic immittance
(tympanometry) evaluations according the standards of the American Academy of Audiology.
The PTA threshold was obtained from the calculated mean of four frequencies (0.5 kHz,
1 kHz, 2 kHz, and 4 kHz). The PTA threshold recognition was set at 120 dB HL. The
normal hearing threshold, following international standards, was considered to be
20 dB HL. To classify hearing recovery, our primary outcome, we used the Siegel[11] criteria ([Table 1]). The audiometric assessment was performed upon admission, and on the third and
last IV administration and hospitalization days, prior to any ITY dexamethasone injections,
during HBO, and, to all patients, in the sixth months of follow-up.
Table 1
Siegel[11] criteria of hearing improvement
|
Type of recovery
|
Hearing recovery
|
|
I – Complete
|
Patients whose final hearing level (pure-tone average) is better than 25 dB regardless
of the amount of the gain
|
|
II – Partial
|
Patients who show > 15 dB of gain and whose final hearing level (pure-tone average)
is between 25 dB and 45 dB
|
|
III – Slight
|
Patients who show > 15 dB of gain and whose final hearing level (pure-tone average)
is poorer than 45 dB
|
|
IV – No improvement
|
Patients who show < 15 dB of gain
|
Note: The higher the level, the worse the outcome.
Assessement of Medical History and MetS Definition
When hospitalized, all patients had their medical history taken, including DM, AHT,
HYL, concomitant active medications for these conditions, and smoking habits. The
anthropometric parameters of weight, height and body mass index (BMI) were assessed
by a nursing team on day one.
The criteria used to diagnose MetS were those of the United States National Cholesterol
Education Program Adult Treatment Panel III (NCEP ATP III),[12] with one adapted criterion for abdominal obesity, because waist circumference was
not routinely assessed. Therefore, MetS was considered the presence of 3 or more of
the following elements: 1) blood pressure > 130/85 mmHg or drug treatment for elevated
blood pressure; 2) fasting TG level > 150 mg/dL, or drug treatment for hypertriglyceridemia;
3) HDL level < 40 mg/dL in males, and < 50 mg/dL in females; 4) fasting plasma glucose
level ≥ 100 mg/dL, or drug treatment for hyperglycemia, for patients who had DM; 5)
adapted criteria for abdominal obesity, with BMI > 25 Kg/m2 in both males and females. After this methodological approach, we divided the 81
patients into 2 groups: 48 without MetS (nMetS), and 33 with MetS.
Statistical Analyses
All statistical analyses were performed using the STATA (StataCorp LLC, College Station,
TX, US) software, version 14.1. The continuous variables are presented as means and
standard deviations or medians and interquartile ranges, after the distribution analysis,
and the categorical and ordinal variables, as frequencies and percentages. Associations
between groups were tested for categorical variables with the Chi-squared and Fisher
exact tests. To compare the continuous variables, we used the independent t-test, or, in case of continuous non-normally distributed or ordinal variables, the
Wilcoxon rank-sum test. A multivariate analysis was performed to assess the predictors
of our primary outcome – hearing recovery according to the Siegel[11] criteria – using binary logistic and ordinal regression models to estimate its odds
ratio (OR) and 95% confidence interval (95%CI). Interactions between MetS and other
variables were tested, namely age, gender, and initial PTA. Statistical significance
was set at p < 0.05.
Results
Demographic Characterization of the Study Groups
Overall, we included 81 patients. The nMetS group was composed of 48 patients, and
the MetS group, of 33 patients. [Table 2] summarizes all the relevant demographic and clinical aspects of our sample. Both
groups were similar concerning gender distribution, the affected ear, accompanying
symptoms, smoking habits, and autoimmune profile. On the other hand, nMets patients
were significantly younger than MetS patients (mean age of 46 years versus 60 years
respectively; p < 0.05).
Table 2
Demographic and clinical characteristics of the study sample
|
|
nMetS
(n = 48)
|
MetS
(n = 33)
|
p-value
|
|
Gender – n (%)
|
Female
|
28 (58.3%)
|
17 (51.5%)
|
0.54
|
|
Age (years)
|
Mean ± standard deviation
|
46 ± 15
|
60 ± 10
|
< 0.001*
|
|
Affected ear – n (%)
|
Right ear
|
23 (47.9%)
|
11 (33.3%)
|
0.19
|
|
Accompanying symptoms – n (%)
|
Tinnitus
|
37 (77.1%)
|
21 (63.6%)
|
0.18
|
|
Vertigo
|
15 (31.3%)
|
12 (36.4%)
|
0.63
|
|
Initial pure-tone average (dB)
|
Median (interquartile range)
|
63 (40–103)
|
78 (60–114)
|
0.029*
|
|
Audiogram loss pattern – n (%)
|
Pantonal without cophosis
|
13 (27.1%)
|
16 (48.4%)
|
0.053
|
|
Cophosis
|
15 (31.3%)
|
11 (33.3%)
|
|
Low frenquecies
|
14 (29.2%)
|
2 (6.1%)
|
|
High frequencies
|
4 (8.3%)
|
2 (6.1%)
|
|
Preserved intermedium frequencies
|
1 (2.1%)
|
2 (6.1%)
|
|
Lost intermedium frequencies
|
1 (2.1%)
|
0
|
|
Rescue treatment – n (%)
|
Intratympanic dexamethasone
|
23 (47.9%)
|
25 (75.8%)
|
0.016*
|
|
Number of intratympanic dexamethasone: median (interquartile range)
|
3 (2–3)
|
3 (2–3)
|
0.78
|
|
Hyperbaric oxygen
|
4 (8.3%)
|
4 (12.1%)
|
0.71
|
|
Smoking habits – n (%)
|
Active
|
9 (18.8%)
|
6 (18.2%)
|
0.91
|
|
Body Mass Index (Kg/m2)
|
Mean ± standard deviation
|
24.8 ± 3.8
|
28.8 ± 3.5
|
< 0.001*
|
|
Arterial hypertension – n (%)
|
Known/Active medication
|
12 (25.0%)
|
23 (69.7%)
|
< 0.001*
|
|
Hyperlipidemia – n (%)
|
Known/Active medication
|
19 (39.6%)
|
31 (93.9%)
|
< 0.001*
|
|
HDL (mg/dL)
|
Median (interquartile range)
|
Male 58
(42–80)
|
Female 72
(55–78)
|
Male 46
(35–58)
|
Female 56
(50–66)
|
Male patients: 0.038*
|
Female patients: 0.08
|
|
High-density lipoprotein cholesterol (mg/dL) – global
|
Median (interquartile range)
|
60 (50–79)
|
52 (43–64)
|
0.008*
|
|
Tryglicerides (mg/dL)
|
Median (interquartile range)
|
92 (60–120)
|
111 (106–175)
|
< 0.001*
|
|
Diabetes mellitus – n (%)
|
Known/Active medication
|
0
|
12 (36.4%)
|
< 0.001*
|
|
Fasting glucose blood level (mg/dL)
|
Median (interquartile range)
|
94 (85–101)
|
111 (100–136)
|
< 0.001*
|
|
MetS components – n (%)
|
0
|
19 (39.6%)
|
|
|
|
1
|
19 (39.6%)
|
|
|
|
2
|
10 (20.8%)
|
|
|
|
3
|
|
26 (78.8%)
|
|
|
4
|
|
5 (15.2%)
|
|
|
5
|
|
2 (6.1%)
|
|
|
Serum autoantibodies – n (%)
|
Overall
|
8 (16.7%)
|
8 (24.2%)
|
0.55
|
|
ANA
|
7 (14.6%)
|
7 (21.2%)
|
0.58
|
|
ANCA
|
1 (2.1%)
|
1 (3%)
|
0.69
|
|
Anti-68 kD
|
0
|
0
|
|
Abbreviations: ANA, antinuclear antibodies; ANCA, antineutrophil cytoplasmic antibodies;
anti-68 kD, antibodies to the inner ear antigen; MetS, with metabolic syndrome; nMetS,
without metabolic syndrome.
Note: In the nMets and MetS column, the numbers in bold represents the central tendency
or equivalent. In the last column the numbers in bold are highlighted when there is
any statical significance.
The most common hearing loss pattern on the audiogram was both pantonal loss without
total hearing loss, and total hearing loss. The MetS patients required rescue treatment
with ITY dexamethasone more often than the nMetS group (76% versus 48% respectively;
p = 0.016), and, in the vast majority of the cases, 3 injections were administered.
Both groups recurred to HBO, with a slight preponderance of the MetS group (12% versus
8%; p > 0.05).
As expected, the metabolic and cardiovascular profiles of the MetS group were significantly
worse, with a higher prevalence of AHT, HYL, DM (the latter only present in the MetS
group). Additionally, the mean BMI was of 29 Kg/m2 (borderline class-I obesity), and 79% had the diagnosis of MetS based on the presence
of at least 3 of the aforementioned criteria for it. The TG and HDL serum values were
globally worse in MetS patients. Moreover, the MetS group had more female patients
with a higher mean age (60 years old), which is in line with a 2017 report by Moore
et al.[9]
Hearing Recovery Outcomes
As depicted in [Fig. 1], we found that the nMetS group had an overall better evolution and a significant
improvement in hearing gain compared to the MetS group (20.6 dB versus 8.8 dB respectively;
p = 0.008). However, the nMetS group had a significantly better initial PTA than the
MetS group (62.5 dB versus 77.5 dB respectively; p = 0.029), and, at the end of the follow-up, the nMetS group had a significantly better
median PTA threshold than the MetS group (30.6 dB versus 62.5 dB respectively; p = 0.001). On the other hand, the recovery evolution in the MetS group was less pronounced
and with a lower dB increment. It should be highlighted that despite the fact that
the nMetS group had a better initial PTA, the final gain was significantly higher
in the nMetS group, and even higher than the initial difference between the two groups,
which demonstrates that the results obtained do not just depend on the better starting
point of nMetS patients.
Fig. 1
Evolution of Hearing Recovery among the study sample. The lower, the better, except for the gain. Comparison of the median PTA between
the nMets and Mets groups and overall median dB gain. Abbreviations: ISSHL, idiopathic
sudden sensorineural hearing loss; IV, intravenous; MetS – with metabolic syndrome;
nMetS – without metabolic syndrome.
Regarding the analysis of the primary outcome – hearing recovery accroding to the
Siegel[11] criteria – ([Fig. 2], [Table 3]) the nMetS group obtained better results (p = 0.001), with complete recovery (Siegel I) in almost 50% of the patients.
Fig. 2
Siegel Recovery Outcome. The higher the level, the worse the outcome.The nMetS group had significantly better
outcomes (p = 0.001). Abbreviations: MetS – with metabolic syndrome; nMetS – without metabolic
syndrome.
Table 3
Hearing recovery outcomes after 6 months of follow-up
|
nMetS
(n = 48)
|
MetS
(n = 33)
|
p-value
|
|
RECOVERY
Siegel I and II – n (%)
|
31 (64.6%)
|
9 (27.3%)
|
0.001 *
|
|
NO RECOVERY
Siegel III and IV – n (%)
|
17 (35.4%)
|
24 (72.7%)
|
|
Siegel I – n (%)
|
21 (43.8%)
|
2 (6.1%)
|
0.001 *
|
|
Siegel II – n (%)
|
10 (20.8%)
|
7 (21.2%)
|
|
Siegel III – n (%)
|
4 (8.3%)
|
5 (15.2%)
|
|
Siegel IV – n (%)
|
13 (27.1%)
|
19 (57.6%)
|
|
Subjective improvement (reported by the patient) – n (%)
|
36 (75%)
|
15 (45.5%)
|
0.007 *
|
Abbreviations: MetS, with metabolic syndrome; nMetS, without metabolic syndrome.
The MetS group presented worse outcomes. In fact, when an improvement occurred, it
was rarely complete, and the majority of these patients (73%) did not recover (Siegel
IV) or had a slight recovery (Siegel III).
Overall, ours results showed a clear trend linking MetS to worse outcomes.
Establishing Predictors – Multivariate Analysis
We intended to establish predictors for our hearing recovery outcome, focusing on
our binary recovery variable (explained in [Table 4], [Fig. 3]) and the Siegel recovery ordinal variable, controlling for potential confounders such as age, gender, and
autoimmunity. Every additional 20 dB in the PTA threshold at diagnosis was revealed
to be a predictor of a worse Siegel score in all analyzed models (any level of recovery – OR = 0.64; 95%CI: 0.45–0.93; partial hearing recovery – OR = 0.42; 95%CI: 0.26–0.67; complete hearing recovery – OR = 0.49; 95%CI: 0.29–0.83; and Siegel outcome – OR = 0.54; 95%CI: 0.39–0.76).
Table 4
Results of the multivariate analysis
|
Regression model and outcome
|
Predictors
|
Odds ratio
|
95% confidence interval
|
p-value
|
|
4.1 Any level of hearing recovery
|
Binary logistic regression
Outcome:
1. Any recovery (Siegel I, II, II)
versus
0. No recovery at all
(Siegel IV)
|
With metabolic syndrome
|
0.38
|
0.12–1.24
|
0.10
|
|
Per 20 dB of increment in initial pure-tone average
|
0.64
|
0.45–0.93
|
0.018*
|
|
Female
|
2.46
|
0.88–6.92
|
0.09
|
|
Per 10 years of increment in age
|
0.97
|
0.65–1.44
|
0.87
|
|
Serum autoantibodies
|
0.85
|
0.25–2.86
|
0.79
|
|
4.2 At least partial hearing recovery
|
Binary logistic regression
Outcome:
1. Recovery
(Siegel I, II)
versus
0. No recovery (Siegel III, IV)
|
With metabolic syndrome
|
0.33
|
0.09–1.23
|
0.10
|
|
Per 20 dB of increment in initial pure-tone average
|
0.42
|
0.26–0.67
|
< 0.001*
|
|
Female
|
3.16
|
0.97–10.26
|
0.06
|
|
Per 10 years of increment in age
|
0.87
|
0.56–1.36
|
0.54
|
|
Serum autoantibodies
|
1.13
|
0.31–4.15
|
0.86
|
|
4.3 Complete hearing recovery
|
Binary logistic regression
Outcome:
1. Complete recovery (Siegel I)
versus
0. Without complete recovery
(Siegel II, III, IV)
|
With metabolic syndrome
|
0.22
|
0.04–1.32
|
0.10
|
|
Per 20 dB of increment in initial pure-tone average
|
0.49
|
0.29–0.83
|
0.008 *
|
|
Female
|
1.94
|
0.54–7.04
|
0.31
|
|
Per 10 years of increment in age
|
0.64
|
0.38–1.08
|
0.10
|
|
Serum autoantibodies
|
1.54
|
0.34–7.07
|
0.97
|
|
4.4 Better Siegel outcome
|
Ordinal logistic regression
Outcome:
Ordinal Siegel hearing recovery level
|
With metabolic syndrome
|
0.30
|
0.10–0.85
|
0.023*
|
|
Per 20 dB of increment in initial pure-tone average
|
0.54
|
0.39–0.76
|
< 0.001*
|
|
Female
|
2.40
|
0.96–5.99
|
0.06
|
|
Per 10 years of increment in age
|
0.86
|
0.62–1.21
|
0.40
|
|
Serum autoantibodies
|
1.02
|
0.34–3.08
|
0.97
|
Fig. 3 Better Siegel outcome 4.4 regression model – odds ratio plots.
Concerning the impact of MetS on the prognosis of recovery from ISSHL, only the 4.4
regression model ([Table 4]) showed evidence that it was a risk factor for a worse hearing outcome (OR = 0.30;
95%CI: 0.10–0.85), controlling for age, gender, initial PTA, and autoimmunity. So,
in this model, a MetS patient has a 70% decrease in the odds of a better outcome.
Of all the tested regression models, we emphasize the “4.4,” ([Table 4]) since it is more comprehensive, inclusive, and covers all possible hearing recovery
outcomes. The test of the interaction among variables, namely MetS and age, gender
and initial PTA, did not reveal significant results (all p-values > 0.20). Therefore, having MetS and a higher initial PTA threshold are predictors
of a worse outcome. We also noted a trend, although not significant, towards better
outcomes among women.
Discussion
The interest in the relationship between MetS and ISSHL is recent, and only in 2015[13] it was first reported. Although the diagnosis of ISSHL as an audiometric entity
does not generate discussion, the true causes underlying ISSHL are still unknown.[1]
[2] This awareness arose when it was noticed that not all patients developed a similar
pattern of symptoms, and, in this cohort, regardless of MetS concomitancy, more than
60% of patients end up having tinnitus, which itself may be the manifestation of hypoacusis.[14] Even when analyzing the initial ISSHL audiometric curve, the authors14 did not identify a typical one. So, even though it is clear when patients have sudden
hearing loss, it is still intriguing if they all really have the same underlying condition.
For many years, it was believed that the etiology of ISSHL would be closely linked
to viral and even vascular causes.[1]
[2]
[14] Therefore, there is still a long path to identify the etiopathogenesis of sudden
hearing loss, at least in the cases referred to as idiopathic. In the present study,
the cases were identified as idiopathic taking into account our exhaustive protocol,
which excludes classic viral/infectious, vascular, autoimmune, and oncological causes.
Accordingly, other studies[2]
[5]
[6]
[7]
[13]
[15] were published, which attempted to correlate ISSHL with other potential risk factors
such as cardiovascular, metabolic, or autoimmune conditions. One of the factors that
will definitely help to explain the pathophysiological mechanism, and even refine
the diagnosis of sudden hearing loss, is the improvement in imaging exams, namely
high-field magnetic resonance imaging of the inner ear.[16]
[17]
In the present article, our hypothesis focused on the possible relationship between
the prevalence of MetS and worse hearing recovery outcomes after ISSHL, since MetS
has an increasing incidence worldwide,[9] in Europe,[8] and particularly in Portugal[10] (with prevalence rates very close to those of the the United States: ∼ 23%). Supporting
our hypothesis, Zhang et al.,[15] in 2019, published a study with a robust sample size, and concluded that MetS had
a negative effect on hearing recovery. However, this study was based on an Asian population
with characteristics different from those of the sample of the present study, particularly
younger patients (42 to 44 years old), and the multivariate analysis was performed
only from the point of view of recovery as a binary outcome. In the present study, we decided to complete this analysis considering
all stages of the Siegel outcomes. We reinforce this, since a binary-outcome analysis
of recovery (Siegel I, II) versus no recovery (Siegel III, IV) would lose the discriminatory power of the best recovery cases (Siegel
I). This is precisely what was observed in the present study: recovery – nMets: 65%; MetS: 27% versus Siegel I – nMets: 44%; MetS: 6% ([Table 3], [Fig. 2]), with clear overestimation of the success of the MetS group in the first binary-outcome
analysis. Additionally, Zhang et al.[15] did not mention neither controlled for autoimmunity.
The mechanism underlying worse outcomes among MetS patients is still speculative.
For instance, insulin resistance and the consequent hyperglycemia, as well as hyperlipidemia
and prothrombotic/proinflammatory states,[12] which are characteristics of MetS, can lead to endothelial changes in small vessels
that can be harmful to the cochlea and the microcirculatory vessels of the Corti organ,[12]
[13]
[15] potentially leading to worse outcomes. Diabetes mellitus is consistently associated
with a worse recovery after ISSHL,[5] and, even in the sample of the present study, 8 out of the 12 DM patients presented
no recovery, and 6 of these, Siegel IV. In summary, in addition to observing that
the sum of each MetS diagnostic criteria was negatively associated with worse outcomes
in terms of hearing recovery, we conclude, based on our sample, that these patients
will require more rescue treatments, despite the burden of their own morbidity.[13]
[15]
[18] Thus, the rescue treatments (ITY dexamethasone and HBO) offered since the beginning
of the treatment might be a potential intervention of choice in these patients.
As we would expect, the initial PTA threshold appears crucial for the success of the
recovery, as demonstrated in other studies.[2]
[13]
[15] This is likely due to the size of injured cochlear area (hair cells), which would
be linked to a worsening of the initial PTA.[19]
The main limitations of the present work were the retrospective methodology and the
fact that the exact time of exposure to MetS was not properly recorded or corrected
for each patient. Even though the BMI calculation was an alternative and valid metric
for the waist circumference to consider as a MetS diagnostic criterion, we believe
it was a fair approach. Finally, we acknowledge that the fact that the HBO center
was not located within our facilities may have led some patients to refuse this option,
with the aggravating factor that this could not always be performed in the first 14
days, as recommended.[1]
[2]
Conclusion
We highlight, as a clear answer to our research question, that MetS is a risk factor
for a worse outcome in terms of hearing recovery after ISSHL, regardless of age, gender,
initial PTA and autoimmunity. We emphasize that all patients diagnosed with ISSHL
should be actively inquired about elements that may underlie a possible case of MetS,
since this can affect the prognosis of the patients.
