###### Abstract
However, studies using otoacoustic emissions (OAEs) [6] to track changes induced by high amplitude noise exposure [7] and ototoxic medications [8] have shown significant changes in OAEs, often occur prior to changes in audiometric hearing thresholds. Therefore, OAEs may be a useful prognostic predictive factor of hearing improvement in patients with ISSNHL from initial onset of symptoms through recovery. OAEs are a low-level sound emitted by the inner ear either spontaneously or in response to an auditory stimulus as a byproduct of typically active cochlear amplification [6]. OAEs are closely associated with function of cochlear outer hair cells (OHCs) and reflect the integrity of the cochlea. Present OAEs denote that OHC function is normal or near-normal, which is often associated with normal to near-normal peripheral auditory function or hearing. When OAEs are present with known abnormal peripheral auditory function or hearing loss, this means that the OHCs are functioning and are not the main cause of the recorded hearing loss (e.g., inner hair cell loss, auditory neuropathy). Successful measurement of OAEs is also dependent upon a healthy middle ear system; middle ear dysfunction interferes with the measurement of OAEs by reducing the eliciting stimuli amplitude (when evoked) and attenuating the emission travelling through the middle ear to be recorded in the ear canal (see [PERSON] et al. for a review [9]). Distortion product otoacoustic emissions (DPOAEs) are elicited by two simultaneous tones at closely spaced frequencies. DPOAEs may be used to evaluate both passive and active cochlear processing to determine auditory function. Active cochlear amplification is elicited with moderate intensity stimuli (e.g., 65, 55 dB SPL). Passive cochlear amplification is elicited with a stimulus of \(\geq\)70 dB SPL and is not dependent on the somatic motility of the OHC [10]. DPOAEs can be recorded in individuals with a mild to moderate hearing loss (thresholds of 40-50 dB HL), making them clinically useful for monitoring even those with mild to moderate cochlear dysfunction [11; 12]. Transient evoked otoacoustic emissions (TEOAEs) utilize short duration stimuli to evoke a response, such as clicks or tonebursts. They are typically absent if pure tone thresholds exceed 30 dB HL [6], and thus are clinically useful as a screening tool and in conjunction with DPOAE to characterize OHC health. Lastly, and unlike DPOAEs and TEOAEs, spontaneous otoacoustic emissions (SOAEs) are sounds emitted from the ear canal that occur without an evoking external stimulus. There are two main theories behind the origin of SOAEs, the global standing wave theory (GST) and local oscillator theory (LOT) [13]. GST suggests that the traveling wave of the basilar membrane between the stapes and cochlear duct creates reflections coupled to a standing wave; in turn, the standing wave vibrates the stapes and is transmitted into the ear canal via backward transmission [14; 15]; LOT suggests the emission may be a result of instabilities of OHCs generating sinusoidal oscillations, without being coupled to a standing wave [16]. They are measurable in ~80% of ears with clinically normal hearing [17], but their absence is not an indicator of dysfunction. OAEs are highly reproducible, have high test-retest reliability, and have temporal/spectral properties that are unique to each individual [6]. They can be performed non-invasively, rapidly, and without the need for reliable behavioral responses [6]. A systematic review of the literature was undertaken to determine if hearing professionals should routinely include otoacoustic emissions in monitoring protocols for ISSNHL. More specifically, does the presence/absence and/or change in OAE characteristics improve clinicians' ability to predict long-term prognosis, that is, hearing recovery? Given that OAEs can objectively measure cochlear function, we predicted that evidence would support the use of OAE to track ISSNHL disease course and recovery.