SSNHL: Etiological Factors, Diagnosis, and Treatment

Sudden sensorineural hearing loss (SSNHL) requires prompt attention, as early diagnosis and treatment significantly impact recovery. It often appears without warning and can be distressing, making it a critical concern in audiology and otolaryngology. While some cases resolve spontaneously, others may lead to permanent impairment if not properly managed.

Understanding the causes, diagnostic tools, and treatments is essential for healthcare providers and patients.

Clinical Presentation

SSNHL manifests as an abrupt decline in hearing, typically in one ear, over less than 72 hours. The severity varies from mild difficulty distinguishing sounds to profound deafness. Many patients first notice the change upon waking or when using the phone. This rapid onset differentiates SSNHL from other types of hearing loss, which develop gradually.

A common symptom is ear fullness, often mistaken for congestion or fluid buildup, leading to delayed medical evaluation. Tinnitus, affecting up to 70% of cases, presents as ringing, buzzing, or hissing, with intensity ranging from mild background noise to intrusive sounds that disrupt concentration and sleep.

Vertigo occurs in 30-40% of cases, indicating possible vestibular involvement. Severe dizziness can impair balance, cause nausea, and interfere with daily activities. The presence of vertigo alongside hearing loss suggests a broader inner ear disturbance, influencing prognosis and treatment. Some patients also report distorted sound perception, where voices or music seem muffled, distant, or abnormally high-pitched.

Etiological Factors

The causes of SSNHL vary, with multiple mechanisms potentially contributing to auditory dysfunction. While many cases remain idiopathic, research points to infectious agents, autoimmune conditions, and vascular disturbances as possible triggers.

Infectious

Viral infections are frequently linked to SSNHL, with evidence suggesting that certain pathogens directly damage the inner ear or trigger inflammation. Herpes simplex virus (HSV), varicella-zoster virus (VZV), and cytomegalovirus (CMV) have all been associated with sudden hearing loss. Reactivation of latent VZV can lead to Ramsay Hunt syndrome, which presents with SSNHL, facial paralysis, and vesicular eruptions.

Bacterial infections, though less common, can also contribute to SSNHL. Bacterial meningitis, particularly from Streptococcus pneumoniae or Neisseria meningitidis, can cause permanent cochlear damage due to inflammation and fibrosis. Lyme disease, caused by Borrelia burgdorferi, has been reported in some SSNHL cases, especially in endemic regions. Identifying an infectious cause is crucial, as early antiviral or antibiotic therapy may improve outcomes.

Autoimmune

Autoimmune inner ear disease (AIED) is an immune-mediated attack on cochlear structures, occurring in isolation or as part of systemic conditions like lupus, rheumatoid arthritis, or granulomatosis with polyangiitis. Immune cells target inner ear antigens, leading to inflammation and vascular compromise.

Autoimmune-related SSNHL often presents with fluctuating hearing loss, sometimes affecting both ears. Systemic symptoms such as joint pain, skin rashes, or fatigue may indicate an underlying autoimmune disorder. Laboratory tests like antinuclear antibodies (ANA) and erythrocyte sedimentation rate (ESR) aid in diagnosis, though response to corticosteroids is often the key indicator. Early immunosuppressive treatment may help preserve hearing.

Vascular

Vascular insufficiency is a possible mechanism for SSNHL, with disruptions in cochlear blood flow leading to sudden auditory impairment. The inner ear is highly sensitive to ischemic events due to its limited collateral circulation. Studies link SSNHL to cardiovascular risk factors like hypertension, diabetes, and hyperlipidemia, which contribute to endothelial dysfunction and reduced cochlear oxygenation.

Thromboembolic events, including small-vessel occlusions, may also play a role. Research suggests a higher prevalence of prothrombotic conditions, such as antiphospholipid syndrome or elevated fibrinogen levels, in SSNHL patients. Vertebrobasilar insufficiency, which affects blood supply to auditory pathways, has been implicated in cases where SSNHL occurs with dizziness or neurological symptoms. Managing cardiovascular conditions may be relevant in these cases.

Diagnostic Methods

Evaluating SSNHL begins with a detailed medical history and physical examination to distinguish it from conductive hearing loss. Patients are asked about symptom onset, recent infections, medication use, and medical history. Otoscopic examination helps rule out external or middle ear pathology, such as cerumen impaction or otitis media.

Pure-tone audiometry is the primary diagnostic tool, confirming sensorineural involvement if there is a reduction of at least 30 decibels across three consecutive frequencies within 72 hours. This test also helps predict recovery potential. Speech discrimination scores provide additional insight, as poorer word recognition suggests more extensive cochlear or neural damage. Otoacoustic emissions (OAE) testing can assess cochlear hair cell function when audiometry results are inconclusive.

Magnetic resonance imaging (MRI) with contrast is often recommended to rule out structural anomalies, particularly vestibular schwannoma, which can mimic SSNHL. MRI can also detect ischemic changes, demyelinating lesions, or inflammatory processes affecting the auditory pathway. Computed tomography (CT) may be considered if temporal bone fractures or congenital abnormalities are suspected.

Laboratory testing is selectively used based on clinical suspicion. Tests for systemic inflammation (ESR, C-reactive protein) and infections like syphilis or Lyme disease may be performed when relevant. Coagulation studies and lipid panels are considered for patients with cardiovascular risk factors. While no single test definitively diagnoses SSNHL, targeted testing can identify underlying conditions that influence treatment.

Therapeutic Measures

Timely intervention is crucial, as delayed treatment reduces the likelihood of recovery. Corticosteroids are the primary therapy, with oral prednisone or methylprednisolone typically prescribed within two weeks of symptom onset. These medications reduce cochlear inflammation and oxidative stress. A common regimen involves a high initial dose, such as 1 mg/kg per day of prednisone, followed by a gradual taper over 10 to 14 days. Intratympanic steroid injections are an alternative for patients who cannot tolerate systemic corticosteroids or do not respond to oral therapy. This localized approach delivers higher drug concentrations to the inner ear while minimizing systemic side effects.

Hyperbaric oxygen therapy (HBOT) has gained attention as an adjunctive treatment, particularly for severe cases. The inner ear depends on oxygen supply, and HBOT enhances cochlear oxygenation by increasing plasma oxygen levels. Studies suggest that patients receiving HBOT within two weeks of symptom onset experience better recovery than those treated with steroids alone. However, access to HBOT is limited, and its effectiveness diminishes when started later.

Prognostic Indicators

Recovery in SSNHL varies, with multiple factors influencing outcomes. While some patients regain full hearing, others experience only partial improvement or permanent loss. The severity of initial hearing loss is a key prognostic factor, with those having mild to moderate impairment more likely to recover than those with profound deficits. Studies indicate that patients with hearing thresholds better than 70 dB at presentation have a higher probability of recovery. Early improvement within the first two weeks is a positive sign, whereas persistent hearing loss beyond this period suggests a poorer prognosis.

The pattern of hearing loss also affects recovery potential. Low-frequency SSNHL has better outcomes than high-frequency or flat-pattern losses, possibly due to differences in cochlear sensitivity. Accompanying symptoms, such as severe tinnitus or vertigo, refine prognostic expectations. Persistent vertigo suggests more extensive vestibular involvement and is associated with worse recovery, while tinnitus without vertigo is less predictive of long-term impairment.