1. Introduction
Sudden sensorineural hearing loss (SSNHL) is defined as an acute sensorineural hearing loss occurring within 72 hours and characterized by a hearing loss of 30 dB or greater over in at least three contiguous audiometric frequencies [1]. The incidence of SSNHL varies from 5 to 30 per 100000 people [2,3], and the pathogenesis of SSNHL remains unclear. Autoimmune disorders, viral infection, and microvascular injury have been described as one of the etiologies of SSNHL, but none of them are defined definitely [4,5].
MMP-9 is one of the Matrix metalloproteinases (MMPs), which is a large family of zinc-containing calcium-dependent endopeptidases. MMP-9 is mainly distributed in the extracellular matrix and has a function to degrade multiple extracellular components, such as collagen and elastin [6]. Several studies have shown MMP-9 is involved in the pathogenesis of diseases including tumor, cardiovascular, and autoimmune disease. Intriguingly, the results in different diseases were in contrast. The mean serum concentration of MMP-9 in patients with tumors or cardiovascular diseases was higher than in healthy controls, whereas MMP-9 level in patients with autoimmune diseases such as Systemic Lupus Erythematosus (SLE) was lower than in healthy controls [7-11]. In our previous study, we delineated that the serum level of MMP-9 in patients with SSNHL was lower than in healthy controls, and the result was in line with autoimmune diseases rather than tumors or cardiovascular diseases [12]. Therefore, to further provide evidence that immune disorder was the main pathogenesis of SSNHL, we collected serum from 52 patients with SSNHL prior to and following treatment with detecting the serum concentration of MMP-9 by ELISA. We hypothesized the mean serum concentration of MMP-9 following treatment elevated in treatment responders and the elevation was associated with favorable outcomes of patients with SSNHL.
2. Materials and methods
2.1 Audiometric Evaluation
All the patients received pure-tone audiometry (PTA) before
treatment、following a one-week and two-week treatment. Mean pure-tone
audiograms was defined as the average of air-conduction threshold
measured at 500,1000,2000,4000HZ and was employed to describe outcomes
of patients.
Four types of audiograms were identified according to the initial
pattern of hearing loss with PTA: ascending (the average threshold of
0.25 to 0.5 kHz was 20 dB higher than the average threshold of 4 to 8
kHz.), descending (the average threshold of 4 to 8 kHz was 20 dB higher
than the average threshold of 0.25 to 0.5 kHz), horizontal (Less than
20dB threshold difference observed across all frequency and the mean
hearing threshold of 0.5,1,2 and 4KHZ was no more than 80dB), profound
(similar audiogram shapes to the horizontal group, whereas the average
threshold of 0.5,1,2 and 4KHZ was no less than 81dB).
As indicated in Chinese clinical practice guidelines of SSNHL [13],
patients were stratified into four groups based on their responses to
treatment (criteria were shown in Table. I): Nonrecovery (NR), partial
improvement (PI), marked improvement (MI) and complete recovery (CR).
Patients in the NR group were defined as the treatment non-responders,
while patients in the other three groups were defined as the treatment
responders.