Idiopathic Sudden Sensorineural Hearing Loss (ISSNHL) is defined as a rapid loss of hearing that occurs over a period of less than 72 hours, typically affecting one ear. This condition is characterized by a significant drop in hearing, specifically 30 decibels or more across at least three connected frequency ranges on an audiogram. ISSNHL is considered a medical emergency requiring immediate attention because effective treatment is highly time-sensitive. The term “idiopathic” is used because, in approximately 90% of cases, the underlying cause remains unknown.
Recognizing the Symptoms and Urgency
Patients frequently discover the abrupt hearing loss upon waking or when using the affected ear during a phone call. The onset is usually accompanied by other inner ear symptoms, such as tinnitus, which is described as ringing, buzzing, or roaring sounds. A feeling of fullness or pressure in the ear is also commonly reported.
Because the inner ear manages balance, 30% to 60% of patients may also experience dizziness or vertigo. It is necessary to seek medical care immediately upon noticing these symptoms, as the prognosis is directly linked to the promptness of intervention.
The period immediately following the onset of symptoms is often referred to as the “72-hour window,” which is the most important time for starting treatment. Delaying treatment beyond this initial period can significantly reduce the chances of a complete or substantial recovery, as the delicate hair cells in the cochlea may sustain irreversible damage. Although therapy can still be beneficial up to two to four weeks after onset, the best outcomes are observed when treatment begins within the first few days.
Understanding the “Idiopathic” Nature
The unknown origin of ISSNHL has led researchers to develop several scientific theories to explain the sudden damage to the cochlea or the auditory nerve. These hypotheses guide the initial medical approach and are generally categorized into three main areas: viral infection, vascular compromise, and autoimmune disorders.
The viral theory suggests that a reactivated or new viral infection, such as those caused by the herpes family, may directly inflame or damage inner ear structures. Evidence supporting this includes the moderate prevalence of a recent viral illness in affected patients. However, a direct viral cause is rarely proven, making the evidence largely circumstantial.
The vascular compromise hypothesis proposes that reduced blood flow to the inner ear causes oxygen deprivation, leading to the rapid death of cochlear hair cells. Because the cochlea is supplied by a terminal artery, it is particularly vulnerable to circulatory issues, which aligns with the sudden nature of the hearing loss. Another element is autoimmune inner ear disease, where the body’s immune system mistakenly attacks the inner ear tissues.
Diagnostic Procedures
Diagnosis begins with a physical examination, including otoscopy, to rule out conductive causes of hearing loss like earwax blockage or middle ear fluid. Since ISSNHL is a diagnosis of exclusion, the primary goal is to confirm the sensorineural nature of the loss and eliminate other identifiable pathologies. The definitive test for confirming the hearing loss is pure-tone audiometry, which measures hearing thresholds across different frequencies.
The audiogram must show a loss of at least 30 dB across three consecutive frequencies to meet the formal criteria for sudden sensorineural hearing loss. This test quantifies the severity and pattern of the damage. Further investigation often involves imaging, typically a Magnetic Resonance Imaging (MRI) scan of the internal auditory canal and brain.
The purpose of the MRI is to exclude retrocochlear lesions, such as an acoustic neuroma, which is a benign tumor that can press on the auditory nerve and mimic ISSNHL symptoms. Imaging is a standard part of the diagnostic protocol because these tumors are a treatable cause of sensorineural loss. Blood tests may also be ordered to check for underlying systemic issues, including autoimmune markers, infections, or metabolic disorders.
Primary Treatment Approaches
The standard medical intervention for ISSNHL is the administration of corticosteroids, which are anti-inflammatory medications. Corticosteroids are believed to reduce swelling and inflammation within the cochlea, addressing the presumed inflammatory or immune components of the condition. The success of this treatment is closely tied to how quickly it is initiated following the onset of hearing loss.
There are two primary methods for delivering steroid treatment: oral and intratympanic. Oral steroids, such as prednisone, are taken systemically and are non-invasive. Intratympanic injections involve a specialist injecting the steroid directly into the middle ear space, allowing the medication to diffuse into the inner ear fluid. Intratympanic delivery is often used as a salvage therapy if oral steroids fail, or as a primary option for patients who cannot take oral steroids.
Hyperbaric Oxygen Therapy (HBOT) is sometimes used as an adjunctive therapy, involving breathing 100% oxygen in a pressurized chamber. HBOT is intended to increase the oxygen concentration in the inner ear fluid, potentially reducing damage caused by oxygen deprivation. While some studies suggest HBOT can improve outcomes when combined with steroids, its effectiveness as a stand-alone treatment remains a subject of ongoing debate. Spontaneous recovery can occur in 30% to 60% of cases, and prompt treatment leads to partial or complete hearing recovery for a significant number of patients.