Non-Organic Hearing Loss: Practical Strategies for the Retail Hearing Care Professional

The majority of articles (80.7%) favoured using PTA as a basis for measuring hearing threshold levels, which was unsurprising given its long history. The Hughson–Westlake method is a widely used method of assessing hearing threshold levels to produce an audiogram. It consists of a series of puretones presented one at a time unilaterally in a descending–ascending manner which relies on the positive or negative responses from the client before proceeding to the next presentation. The main issue that an HCP may encounter using this method, is the high reliance on the client’s subjective input and their ability to manipulate loudness perception and adjust responses accordingly. Thompson’s study showed the two most used strategies in ‘malingering participants’ (2017, p. 2). One was maintaining a consistent interval between responses and the second was comparing the tones to the participant’s perception of what was ordinarily a soft, average and loud sound. A modified ascending technique instead of the Hughson–Westlake method, improved thresholds between 34.5–36dB (Balatsouras et al., 2003). Where there is a difference between ascending and descending technique results in the puretone average of 5dB or more, consider NOHL (Martin et al., 2000; Musat et al., 2013).

When performing audiometry with a NOHL client, try ‘jumping’ between traditional frequency sequencing to limit anticipation and familiarity (ASHA, n.d). In some cases, it may be helpful to start at a different frequency, use a warble stimulus, change between ears regularly or even put a low level of masking in one ear intermittently during the test. Lengthening the duration of tone stimulus and increasing the interval times between presentations assisted in improving thresholds (Balatsouras et al., 2003; Martin & Clark, 2015).

This useful test can be performed relatively easily in a retail audiology clinic because of the accessibility to standard equipment. The majority of articles (73%) mentioned the usefulness of ARTs. Psarommatis et al. (2009, p. 1860) cautioned against “relying on this for threshold determination” because of physiological variances, which was strongly supported by Al-dujaily (2015). The bilateral reflex occurs at high intensities essentially increasing acoustic impedance. The ART is generally 70–95dB above the 3 Frequency Average Hearing Level (3FAHL) or ‘puretone average’ in normal hearing ears (Al-dujaily, 2015; Musat et al., 2013; Zhao et al., 2008) although it can be “absent in a small number” of this population (Mistry et al., 2016, p. 6). It can also be limited in the presence of an organic sensorineural hearing component due to cochlear recruitment (Balatsouras et al., 2003; Martin & Clark, 2015). The difference between ipsilateral and contralateral acoustic reflex thresholds are between 5–10dB.

Physiology of ART. The physiology enabling this reflex is controlled primarily by the lateral superior olivary which determines the relative intensity of sound stimulus. It controls efferent fibres to the olivary cochlear bundle triggering prestin in the outer hair cells lengthening the cell and reducing the action potentials, to protect against loud sounds. The reticular formation activates the facial and trigeminal nerves which lead to the middle ear via efferent pathways. The facial nerve enervates the stapedial muscle that is connected to the stapes. This muscle contraction restricts the movement of the stapes on the oval window (Feeney & Schairer, 2015). The trigeminal nerve leads to the tensor tympani, attached to the medial part of the malleus, contracting the muscle thus tightening the tympanic membrane, dampening sound stimulus by stiffening the ossicular chain. The contractions result in a change in compliance of the tympanic membrane indicating the loud stimulus was processed by the auditory system (Lin & Staecker, 2006).

A reflex is not usually present with hearing losses greater than the moderately–severe degree, if it is, this test further supports the possibility of NOHL. If the reflex is present within 5–10dB sensation level below (louder) the hearing threshold, it can indicate NOHL (Lin & Staecker, 2006; Martin & Clark, 2015). If the ART is elicited above (softer) the purported hearing threshold, it should be taken as a strong indication of NOHL (Al-dujaily, 2015; Thiagarajan, 2012).

OAEs are low–intensity sounds generated by the stereocilia in the outer hair cells of the cochlea which are measured in the external auditory meatus (Balatsouras et al., 2003; Lin & Staecker, 2006; Prieve & Fitzgerald, 2015). Hearing loss caused by damage to the outer hair cells results in a reduction in or absence of OAEs (Al-dujaily, 2015). OAEs do not evaluate the integrity of the inner hair cells or neural transmission (Durmaz et al., 2009; Lin & Staecker, 2003) nor are they a substitution for puretone audiometry as they do not provide hearing loss degree or type (Rasetshwane, Fultz, Kopun, Gorga, & Neely, 2015).

This electrophysiological test is objective and non–invasive, which broadly assesses cochlear function in the absence of middle ear pathology or ear canal obstruction. Two common evoked OAEs are Distortion Product Otoacoustic Emissions (DPOAEs) and Transient Evoked Otoacoustic Emissions (TEOAEs). Both are expected to provide results where the hearing thresholds are 30dBHL or better. The majority of authors (18 / 26 or 69.2%) supported using OAEs (with 6 / 18 indicating a preference for TEOAEs and 3 / 18 for DPOAEs). These are relatively uncontroversial and have had the benefit of years of testing so enjoy a high acceptance within the clinical community. Rasetshwane et al. (2016) contended that both methods provide reliability and high sensitivity in normal hearing ears, however it is dependent on the stimulus level and frequency.

TEOAEs. Uses a short click or tone–burst wideband stimulus between 1–4kHz, measuring emissions between the clicks, which stimulates a greater area of the basilar membrane of the cochlea (Rasetshwane et al., 2015). TEOAEs are not usually present in hearing losses greater than 30–40dBHL and provide a weaker correlation to the puretone audiometry results (Al-dujaily, 2015: Morita et al., 2010; Rasetshwane et al., 2015).

DPOAEs. Presents two puretones simultaneously between 1–10kHz (equipment dependent) and the emissions are measured during the stimulus presentation and are not usually present in hearing losses greater than 40–50dBHL (Durmaz et al., 2009; Rasetshwane et al., 2015). DPOAEs provide better frequency–specific indications above 1kHz and have a stronger correlation to the puretone audiometry results (Balatsouras et al., 2003; Rasetshwane et al., 2016).

A speech test assesses the ability of a person to understand and discriminate speech. There are two important factors involved with the intensity of a speech signal and the listener’s ability to both detect and understand (Schlauch & Nelson, 2015). The Speech Reception Threshold (SRT) is the lowest intensity that a person can understand and detect 50% of spondaic words correctly. It is used to cross–validate the audiogram and a person with normal hearing should score close to 50% correct at 30dBHL (Lin & Staecker, 2006; McArdle & Hnath-Chisolm, 2015). Half of the reviewed authors favoured this test. In NOHL cases, the SRT is typically better than the 3FAHL, indicating disparity. Thompson’s study (2017) supported this assertion with over 86% of participants having a significantly better SRT than 3FAHL.

          Agreement with Puretone Average. The 3FAHL, or puretone average, is calculated as the average of the air–conduction thresholds at 500Hz, 1kHz and 2kHz for each ear. The 3FAHL should agree closely with the SRT (Al-dujaily, 2015). Kreisman et al. (2015, p. 120) recommended using a two-frequency hearing level average for sharply sloping or rising audiograms, to prevent SRT being better than PTA.

          Acceptable Variance. The literature revealed a small variance of acceptable limits between the 3FAHL and SRT, of 10–20dB. Georgescu et al. (2014) stated the puretone average should be within 10dB, whereas Schlauch et al. supported 12dB (2015), Lin and Staecker (2006) and Holenweg and Kompis (2010) accepted 15dB of the SRT. Drouillard et al. (2014) allowed a 20dB difference which was the largest variance found in the literature. The majority however, applied 10dB.

The majority of authors favoured the Stenger test, which can be used in asymmetrical losses (of no less than 10dB–40dB) or unilateral losses (Durmaz et al., 2009; Martin & Clark, 2015; Norrix et al., 2017). The combined reliability of sensitivity, specificity and predictive value was reported to be between 70–99.4% (Durmaz et al., 2009; Georgescu et al., 2014). It is an effective, useful test for NOHL, yet seems to be underused in this country. When two sounds of the same frequency but at different intensities are presented simultaneously, the brain perceives one central sound as a result of “binaural fusion” which localises to the better ear (Lin & Staecker, 2006, p. 322; Martin & Clark, 2015, p. 617; Norrix et al., 2017, p. 1). It can be performed using tuning forks, but the contemporary method is via a two–channel audiometer under headphones or inserts.  

Positive or Negative Stenger. The literature revealed a small variance of the initial presentation level. Authors recommended between 5–20dB (Durmaz et al., 2009; Musat et al., 2013). In a screening Stenger, the first presentation level is generally 5–20dB softer than the purported threshold in the poorer ear and 5–20dB louder than the threshold in the better ear. Both tones are suprathreshold—the tone is louder than the true threshold of the poorer ear which prevents the better ear from hearing the tone (Martin & Clark, 2015; Norrix et al., 2017). Usually, the NOHL client will not respond, because they are trying to maintain that they have a poorer hearing ear (Norrix et al., 2017).

A ‘positive Stenger’ means the client did not respond, which indicates the tone was heard in the poorer ear, because the tone lateralised to the best ear. A ‘negative Stenger’ is obtained when the client acknowledges the tone, indicating it was perceived in the better ear and is considered an appropriate response. The Stenger test can use either puretones or speech and the same principles apply to speech as to tonal stimuli (Martin & Clark, 2015).

The greatest limitation of the Stenger test is that it cannot be used in symmetrical hearing losses. Rowan, Morris, Adewale and Millgate (2012) studied a Tone–in–Noise (TIN) test which can be used in bilateral NOHL. It compares PTA under ipsilateral narrowband masking, i.e., the tone and masking is presented in the same ear. The concept was that ‘supra–threshold noise would interfere with a subject’s judgement when feigning’ (Rowan et al., 2012, pp. 179, 182). A limitation here is the potential of the masking to cause a threshold shift. A simple test similar to the TIN that can be used in bilateral symmetric losses, would be helpful for the HCPs toolkit. Further research in this area would be highly beneficial in identifying NOHL.

Although only 38.4% of the articles mentioned tympanometry, it was included given its close association to the ART and the equipment that is used. Tympanometry is a commonly used test in retail audiology clinics. It is an objective, physiological measure of acoustic admittance and impedance of the middle ear which is graphically depicted. The pressure variance causes the tympanic membrane and ossicles to flex and stiffen, demonstrating increased and decreased admittance to sound energy. Peak admittance is greatest when middle ear pressure is equal to the atmospheric pressure. Tympanometry is an indicator of middle ear pathology which might impact the PTA results. The HCP can be more informed about this possibility before proceeding to PTA and better able to account for its involvement. There are longstanding accepted types and norms for tympanometry which are associated with various middle ear conditions (Hunter & Sanford, 2015).