Challenges in Diagnosing Sudden Sensorineural Hearing Loss

Idiopathic sudden sensorineural hearing loss (ISSNHL) is a medical emergency that hearing care professionals frequently encounter. Despite being identified over a century ago, ISSNHL remains a clinical enigma, in terms of both diagnosis and management. Unlike the majority of disorders causing hearing loss in adults, which progress slowly and quietly, ISSNHL is a frightening and mysterious event due to its sudden, often unannounced appearance. ISSNHL is defined as a unilateral acute sensorineural hearing loss of 30 decibels or more over at least three contiguous frequencies, occurring within 72 hours. It has an estimated annual incidence of 5 to 27 per 100,000 persons,¹ which is likely an underestimate because spontaneous hearing recovery may discourage some patients from seeking medical attention. The incidence may vary from country to country possibly due to the different health care systems across the globe.

Figure 1: Proposed ways of managing ISSNHL. Abbreviations: AC, Air Conduction; BC, Bone Conduction; ISSNHL, Idiopathic Sudden Sensorineural Hearing Loss.

Hearing loss in ISSNHL has been linked to damage to the cochlea or auditory nerve, which, if not treated promptly, can leave patients with permanent hearing deficits. It can happen to anyone at any time, regardless of age or previous hearing problems. Although ISSNHL can be caused by a multitude of factors, around 90% of the cases are idiopathic, where no definitive underlying cause can be determined at the time of presentation, and treatment decisions are made even before the cause is determined.² It is regarded as a medical emergency because the hearing can be recovered, often completely, if prompt action is taken. Therefore, the evaluation of the patient should be done as soon as possible since the prognosis is directly proportional to the time taken between onset of symptoms and initiation of treatment.

RECOGNIZING AND DIAGNOSING ISSNHL

Clinical features of ISSNHL include unilateral rapid onset of hearing loss, with or without associated symptoms such as tinnitus, vertigo, and stuffy ear. Evaluation of the patient includes taking a comprehensive history of onset, duration and laterality of hearing loss along with associated symptoms like headache, tinnitus, dizziness, focal neurological deficits, and predisposing factors like infection, trauma, or excessive alcohol consumption. This may help narrow down the differential diagnosis and determine the urgency for a referral as required. The sensation of a stuffy or full ear should not deter the examining physician from suspecting ISSNHL as the underlying condition.

Aural fullness, tinnitus, and muffled hearing are the most common symptoms, which are typically non-specific. As a result, the first step in diagnosis is to determine the type of asymmetrical hearing loss, whether conductive hearing loss (CHL) or sensorineural hearing loss (SNHL). To check for hearing asymmetry in the office, softly whisper simple words or numbers in each ear and ask the patient to repeat them aloud, move the phone from ear to ear, or crumple paper near the ear on each side. To determine whether the hearing asymmetry is due to conductive causes, ask the patient to hum to themselves and report whether the sound is louder in the better or the poorer ear. Sound lateralizes to the poorer ear in CHL, whereas sound lateralizes to the better ear in SNHL.

Clinically, Rinne and Weber tests are used to differentiate between CHL and SNHL. In the case of CHL, the bone conduction is better than air conduction on Rinne, and the sound lateralizes to the poorer ear on Weber, whereas the opposite is true for both tests in SNHL. Therefore, tuning fork tests (TFTs) must be employed as the standard test to differentiate the types of asymmetrical hearing loss clinically. This makes the diagnosis of ISSNHL faster and easier and rules out the common causes of CHL for which it is otherwise mistaken. Once a diagnosis of asymmetrical sudden SNHL is established with TFT, a pure tone audiometry should be performed at the earliest to confirm the diagnosis so treatment can be initiated without much delay.

An early intervention of oral steroid regimen initiated preferably within two weeks of onset of symptoms, with a standard dose of 1 mg/kg/day for 7-10 days followed by tapering, is still the most commonly prescribed therapeutic regimen for ISSNHL around the world. Intratympanic steroid therapy may be recommended in patients with contraindications to systemic steroid therapy, or even as a salvage therapy in patients with no benefit from systemic treatment. Hyperbaric Oxygen therapy is another modality of treatment that has been tried in patients who present within three months of onset of ISSNHL and have severe to profound hearing loss at baseline.³ The efficacy of different treatment modalities are shown to be similar^4,5 so the treatment prescribed depends greatly on the access to the available options.

CHALLENGE(S) IN DIAGNOSIS

ISSNHL patients may report to an emergency physician, a family physician, a nurse practitioner, an audiologist, or an otolaryngologist, depending upon the health care system followed in their place of residence. In countries with private health care systems, patients may present to an otolaryngologist directly and prompt treatment may be initiated without much delay, increasing the likelihood of therapeutic success. In universal health care systems, the patient commonly presents to the family physician or nurse practitioner, who would be the patient’s primary care provider. Prompt recognition of ISSNHL by the primary care provider (PCP) greatly influences the speed at which treatment is initiated, thereby having direct impact on the recovery of hearing. As a result, it is critical that any PCP having first contact with these patients should be familiar with the clinical practice guidelines,¹ and thus play a critical role in identifying potential cases and expediting the most effective management.

The PCPs serve as “gatekeepers,” regulating access to more expensive procedures or to specialists. The most common issue in ISSNHL is a delay in diagnosis, or misdiagnosis, because patients and clinicians frequently attribute ear fullness, dizziness, and tinnitus to cerumen impaction, or upper respiratory infection and allergies with fluid accumulation in the middle ear, resulting in a delay in diagnosis of ISSNHL. Evidence suggests that the degree of hearing recovery in ISSNHL is directly proportional to the time interval between onset of symptoms and initiation of treatment; therefore, it is imperative to diagnose the condition promptly and initiate treatment at the earliest.

TFT is one of the most reliable tests in differentiating CHL and SNHL. The majority of patients with alternative diagnoses routinely considered, like cerumen impaction, Eustachian tube dysfunction, or otitis media, will have CHL. Weber test has proven to be highly sensitive in detecting the affected ear in individuals with ISSNHL, thereby making it possible to differentiate between CHL and SNHL. Also, the gold standard audiometric testing with adequate masking is frequently unavailable in primary care settings, requiring the patient to travel elsewhere for urgent audiometry, delaying diagnosis and treatment initiation, so clinical diagnosis becomes critical. A recent study revealed that the TFTs are underutilized among PCP for distinguishing CHL and SNHL, owing to the lack of confidence in administering and interpreting the results.⁶ PCPs should use TFTs, in conjunction with otoscopy and thorough case history, to promptly diagnose and treat ISSNHL and determine management decisions like the initiation of corticosteroid therapy.

EFFECTIVE MANAGEMENT OF ISSNHL

Audiology and otolaryngology groups should provide PCPs with education addressing the importance of TFTs in early diagnosis and treatment initiation in ISSNHL to improve patient outcomes. The local professional bodies should disseminate the clinical practice guidelines to the primary care physicians, as the majority of patients with ISSNHL report to them. The clinicians who are the first point of contact for the patient should be aware to refer them to an audiologist immediately so delay in diagnosis and treatment may be avoided. If access to an otolaryngologist is possible right after confirmation of the diagnosis by an audiologist, formatted letters designed to bring the urgency of the matter to the attention of the ENT office would greatly improve the manner in which these cases are dealt with. These letters can be sent either by the audiologist or the primary care physicians to the ENT office, and should be designed in a way that is easily interpreted by the office administrators working with the ENTs. If access to a specialist is not readily available, the PCPs should be well equipped to diagnose and treat ISSNHL without much delay. In this situation, oral steroid therapy is preferred due to ease of prescription of the same. Fig. 1 shows the proposed ways for managing ISSNHL.

The means by which awareness on this condition among the general population may be increased include:

• Displaying information in the form of a flowchart or brochures/pamphlets on ISSNHL in all primary health care professionals’ offices;
• Creating awareness on ISSNHL among professionals who are the first point of contact for most patients, e.g., nurse practitioners, physician assistants, and office administrative officers;
• Forming self-help groups online; and
• Creating a sudden hearing loss support website.

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