# Study Guide: Sudden Hearing Loss Clinical Practice Guideline

This study guide is based on the 2019 Clinical Practice Guideline Update for Sudden Hearing Loss. It is designed to assist in the comprehension of diagnostic criteria, management strategies, and rehabilitative outcomes for adult patients (aged 18 and older) presenting with sudden hearing loss.

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## I. Core Concepts and Definitions

Sudden hearing loss is a frightening symptom that often results in urgent or emergent medical visits. Understanding the specific subsets of this condition is critical for appropriate triage and treatment.

### Classification of Hearing Loss
*   **Sudden Hearing Loss (SHL):** A rapid-onset subjective sensation of hearing impairment in one or both ears. It can be conductive, sensorineural, or mixed.
*   **Sensorineural Hearing Loss (SNHL):** Hearing loss resulting from abnormal functioning of the cochlea, auditory nerve, or higher central auditory perception/processing structures.
*   **Sudden Sensorineural Hearing Loss (SSNHL):** A subset of SHL that is sensorineural, occurs within a 72-hour window, and meets specific audiometric criteria: a decrease in hearing of $\ge$ 30 decibels (dB) affecting at least three consecutive frequencies.
*   **Idiopathic Sudden Sensorineural Hearing Loss (ISSNHL):** SSNHL with no identifiable cause despite adequate investigation. This accounts for approximately 90% of SSNHL cases.
*   **Conductive Hearing Loss (CHL):** Hearing loss resulting from a problem conducting sound waves through the outer ear, tympanic membrane, or middle ear.

### Clinical Statistics
*   **Incidence:** Affects 5 to 27 per 100,000 people annually.
*   **New Cases:** Approximately 66,000 new cases per year in the United States.
*   **Spontaneous Recovery:** Literature suggests 32% to 65% of cases may recover spontaneously, though clinical experience suggests these numbers may be an overestimation.

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## II. Diagnostic Evaluation and Triage

The primary goal of the initial evaluation is to distinguish sensorineural loss from conductive loss and identify rare but serious underlying causes.

### Distinguishing SNHL from CHL (KAS 1)
Clinicians must differentiate these types at presentation because their management strategies differ significantly.
*   **Physical Examination:** Otoscopy should be performed to check for obstructing cerumen, foreign bodies, tympanic membrane perforation, or middle ear fluid.
*   **Tuning Fork Tests:** The Weber and Rinne tests (using 256 or 512 Hz forks) are essential for initial differentiation. 
    *   **Weber Test:** Fork is placed at the midline; sound lateralizes to the ear with CHL or away from the ear with SNHL.
    *   **Rinne Test:** Compares air conduction (AC) to bone conduction (BC). In CHL, BC > AC.
*   **Hum Test:** An alternative to the Weber test; if a patient hears their own hum louder in the affected ear, it suggests CHL.

### Assessment of Modifying Factors (KAS 2)
Clinicians should look for "red flags" that suggest non-idiopathic causes:
*   Bilateral sudden hearing loss.
*   Recurrent episodes or fluctuating hearing loss (may suggest Ménière’s disease).
*   Focal neurologic findings (may suggest stroke or multiple sclerosis).

### Prohibited Routine Tests (KAS 3 & 5)
*   **Routine Head CT:** Should **not** be ordered for presumptive SSNHL. It lacks the resolution for the internal auditory canal and exposes patients to unnecessary radiation.
*   **Routine Laboratory Tests:** Nontargeted "shotgun" blood work is not recommended as it rarely changes management and may lead to false positives.

### Audiometry and Retrocochlear Evaluation (KAS 4 & 6)
*   **Audiometry:** Should be obtained within 14 days of symptom onset to confirm the diagnosis.
*   **Retrocochlear Workup:** All SSNHL patients must be evaluated for pathology such as vestibular schwannoma (acoustic neuroma). 
    *   **MRI:** The gold standard; highly sensitive for small tumors.
    *   **ABR:** An alternative if MRI is unavailable, though it may miss up to 20% of small tumors.

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## III. Treatment Modalities

Treatment is most effective when initiated early. The guideline emphasizes shared decision-making regarding the following options:

### Initial Therapies (Within 2 Weeks)
*   **Corticosteroids (KAS 8):** May be offered as an option.
    *   **Systemic:** Prednisone 1 mg/kg/d (max 60 mg/d) for 10–14 days.
    *   **Intratympanic (IT):** Direct injection into the middle ear; higher perilymph concentrations with fewer systemic side effects.
*   **Hyperbaric Oxygen Therapy (HBOT) (KAS 9a):** May be offered in combination with steroid therapy within 2 weeks of onset.

### Salvage Therapies (After 2 Weeks)
*   **Intratympanic (IT) Steroids (KAS 10):** Should be offered if there is incomplete recovery 2 to 6 weeks after symptom onset.
*   **HBOT Salvage (KAS 9b):** May be offered within one month of onset as an adjunct to steroids.

### Recommendations Against (KAS 11)
Clinicians should **not** routinely prescribe:
*   Antivirals.
*   Thrombolytics.
*   Vasodilators or vasoactive substances.

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## IV. Short-Answer Practice Questions

**1. What is the "standard" audiometric definition of SSNHL?**
*Answer: A decrease in hearing of $\ge$ 30 decibels (dB) affecting at least three consecutive frequencies occurring within a 72-hour window.*

**2. Why is routine computed tomography (CT) of the head discouraged in SSNHL evaluation?**
*Answer: It does not provide adequate resolution of the internal auditory canal (IAC) to detect small tumors, exposes the patient to radiation and contrast risks, and is often ordered unnecessarily in emergency settings.*

**3. What is the recommended dosage for oral prednisone in the treatment of SSNHL?**
*Answer: 1 mg/kg/day in a single dose, with a usual maximum of 60 mg daily, for 10 to 14 days.*

**4. When should follow-up audiometry be obtained?**
*Answer: At the conclusion of treatment and again within 6 months of the completion of treatment.*

**5. Name three serious non-idiopathic causes of SSNHL that must be ruled out.**
*Answer: Vestibular schwannoma (acoustic neuroma), stroke (particularly AICA occlusion), and malignancy.*

**6. What are the potential complications of intratympanic steroid injections?**
*Answer: Pain, transient dizziness, infection, and persistent tympanic membrane perforation.*

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## V. Essay Prompts for Deeper Exploration

1.  **The Role of Shared Decision-Making:** Discuss the ethical and clinical importance of shared decision-making in the context of ISSNHL. Why is patient education regarding the "natural history" of the disease particularly vital when discussing treatment options like corticosteroids or HBOT?
2.  **Diagnostic Discrepancies:** Compare the utility and limitations of MRI versus Auditory Brainstem Response (ABR) in identifying retrocochlear pathology. Under what specific patient circumstances might a clinician choose ABR over the gold-standard MRI?
3.  **The Challenge of Idiopathic Diagnosis:** 90% of SSNHL cases are labeled "idiopathic." Analyze the proposed pathophysiological mechanisms (viral, vascular, autoimmune) and explain how these theories influence current (though often unproven) pharmacologic interventions.
4.  **Rehabilitative Outlook:** Beyond medical recovery, explore the psychosocial and functional burdens of residual hearing loss and tinnitus. How does audiologic rehabilitation (hearing aids, cochlear implants, counseling) impact a patient’s long-term quality of life?

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## VI. Glossary of Important Terms

| Term | Definition |
| :--- | :--- |
| **AICA** | Anterior Inferior Cerebellar Artery; occlusion can lead to stroke-related hearing loss and vertigo. |
| **ABR** | Auditory Brainstem Response; an electrophysiological test of the auditory nerve and brainstem pathways. |
| **Audiometry** | The testing of a person's ability to hear various sound frequencies. |
| **Cochlea** | The spiral-shaped part of the inner ear responsible for translating sound waves into nerve impulses. |
| **HBOT** | Hyperbaric Oxygen Therapy; treatment involving 100% oxygen at pressures > 1 atmosphere. |
| **Intratympanic (IT)** | Administration of medication by injection through the tympanic membrane into the middle ear. |
| **Mixed Hearing Loss** | A combination of both sensorineural and conductive hearing loss in the same ear. |
| **OAE** | Otoacoustic Emissions; sounds generated by the outer hair cells of the cochlea used to assess cochlear function. |
| **Retrocochlear** | Referring to the area "behind the cochlea," including the auditory nerve and central nervous system. |
| **Salvage Therapy** | Treatment offered after 2 weeks from symptom onset, typically after initial therapy has failed. |
| **Tinnitus** | The perception of noise or ringing in the ears; a frequent comorbidity of SSNHL. |
| **Vestibular Schwannoma** | A benign tumor on the vestibular nerve (8th cranial nerve) that can cause SSNHL; also called an acoustic neuroma. |
| **WRS** | Word Recognition Score; a measure of speech understanding, usually expressed as a percentage. |