From the Guidelines
Sudden sensorineural hearing loss (SSNHL) is primarily caused by vascular compromise, viral infections, or autoimmune processes, with the exact cause often remaining unknown or uncertain at the time of presentation 1. The pathophysiology of SSNHL involves rapid hearing deterioration occurring over 72 hours or less, affecting the inner ear or neural pathways.
- Vascular causes include microcirculation disturbances, thrombosis, or embolism affecting the cochlear blood supply, particularly the labyrinthine artery which lacks collateral circulation.
- Viral infections may directly damage cochlear hair cells or trigger inflammatory responses that impair inner ear function, with herpes viruses commonly implicated.
- Autoimmune mechanisms involve antibodies attacking inner ear structures, disrupting normal hearing function. Additional mechanisms include inner ear membrane ruptures, causing endolymph and perilymph mixing that alters the electrochemical environment necessary for sound transduction.
- Metabolic stress from these processes leads to oxidative damage and apoptosis of hair cells and spiral ganglion neurons. The cochlea's limited regenerative capacity means that damage often results in permanent hearing loss. Treatment typically involves corticosteroids (oral prednisone 60mg daily for 7-14 days or intratympanic dexamethasone 10-24mg/ml) started promptly, as delays beyond 2-4 weeks significantly reduce recovery chances due to irreversible neural degeneration 1. It is essential to approach these idiopathic cases in a common way, understanding that the underlying etiologies may be very dissimilar, and a "team approach" to the overall management of these patients is encouraged 1. Prompt recognition and management of SSNHL may improve hearing recovery and patient quality of life, and clinicians should be aware of the psychological response to the sudden loss of a primary sense, including anxiety, depression, and social isolation 1.
From the Research
Pathophysiology of Sudden Sensorineural Hearing Loss (SSNHL)
The pathophysiology of SSNHL is complex and multifactorial, involving various mechanisms that affect the cochlear microenvironment or its nervous component. Some of the key factors that contribute to the development of SSNHL include:
- Inflammatory changes: Studies have shown that inflammatory markers such as interleukins (IL) and tumor necrosis factor α (TNF-α) play a role in the pathogenesis of SSNHL 2.
- Metabolic changes: Metabolic factors such as lipid and glycemic profiles, as well as concentration of creatinine, uric acid, and fructosamine, may also contribute to the development of SSNHL 2.
- Atherosclerosis and microthrombosis: These factors may also be involved in the etiology of SSNHL, particularly in patients with comorbidities such as cardiovascular disease 3.
- Immune system dysfunction: The immune system may also play a role in the development of SSNHL, with some studies suggesting that autoimmune disorders may be a contributing factor 3.
- Viral infections: Some studies have suggested that viral infections may be a cause of SSNHL, although the exact mechanism is not fully understood 3.
Etiology of SSNHL
The etiology of SSNHL is still not fully understood, but it is thought to be a multifactorial disease. Some of the possible causes of SSNHL include:
- Idiopathic factors: In many cases, the cause of SSNHL is unknown, and it is classified as idiopathic 4.
- Comorbidities: Certain comorbidities, such as cardiovascular disease, diabetes, and autoimmune disorders, may increase the risk of developing SSNHL 3.
- Viral infections: As mentioned earlier, viral infections may be a cause of SSNHL, although the exact mechanism is not fully understood 3.
Systemic Parameters and Hearing Recovery
Studies have shown that certain systemic parameters, such as cytokine levels, may be associated with hearing recovery in patients with SSNHL. For example, one study found that TNF-α levels decreased significantly in patients who achieved complete and significant recovery 2. These findings suggest that systemic changes may be related to improvements in hearing, and that certain biomarkers may be useful in predicting hearing recovery.