8Sudden sensorineural hearing loss
An acute SNHL of at least 30 dB over three consecutive frequencies, developing within 72 hours. Of the patients in front of you, 71–90% will be idiopathic — and ECochG's role in distinguishing the rest is now small.
Adjunct only. The 2019 AAO-HNSF guideline recommends MRI or ABR (not ECochG) to evaluate for retrocochlear pathology; ECochG may help when atypical features raise specific hypotheses (hydrops, third window) but is not part of the standard workup.[2019]
FClinical presentation
The AAO-HNSF defines SSNHL as a sensorineural loss of ≥ 30 dB over three contiguous audiometric frequencies, developing in 72 hours or less.[2019]Incidence is 5–27 per 100,000 per year; bilateral involvement < 2%. Vertigo accompanies 30–60% of cases at presentation. Most patients (71–90%) end up labelled idiopathic SSNHL (ISSNHL) — no identifiable cause emerges from a reasonable workup.[2012]
Nonidiopathic causes that must not be missed include:
- Vestibular schwannoma — present in approximately 1–5% of SSNHL referrals; MRI essential.
- Stroke (AICA territory) — almost always with focal neurology; a small subset present with isolated audiovestibular symptoms.
- Autoimmune inner ear disease — bilateral or rapidly progressive courses raise suspicion.
- Lyme disease, syphilis, HIV, COVID-19 — geography and risk factors guide selection.[2012]
- Ototoxic exposure, recent barotrauma (consider perilymph fistula), trauma.
TWhat ECochG might add
In a typical SSNHL presentation, ECochG shows the expected effect of cochlear damage: reduced AP amplitude proportional to the threshold elevation, prolonged AP latency (a function of where on the audiogram you cross threshold — see Module 4's latency-intensity function), and a variable SP. The pattern looks like a generic cochlear lesion rather than pointing at any specific aetiology.
Two situations in which ECochG can occasionally add diagnostic value:
- Suspected hydropic SSNHL.Some patients present with an SSNHL that turns out to be the first episode of Ménière's disease. An elevated SP/AP ratio supports an underlying hydropic process and may guide longitudinal management. The hit rate is low because most SSNHL is not hydropic, and the test is non-specific.
- Suspected third-window phenomenon. A patient with simultaneous-onset symptoms that overlap with SCD (autophony, sound-induced vertigo, low-frequency air–bone gap), where the question is whether a baseline ECochG is consistent with a third window. Module 6 covers this in more detail.
The 2019 AAO-HNSF guideline is explicit: clinicians should obtain MRI or ABR to evaluate for retrocochlear pathology in patients with SSNHL.[2019] ECochG is not mentioned in the diagnostic recommendations. The reasoning is straightforward — the most consequential miss in SSNHL is a vestibular schwannoma, and gadolinium-enhanced MRI directly visualises the tumour with near-100% sensitivity. ECochG cannot replace that role: as Module 10 covers, ECochG is insensitive to retrocochlear pathology because the AP generator is distal to most schwannomas.
FThe modern SSNHL workup
| Step | Test | Purpose |
|---|---|---|
| 1 | Pure-tone audiometry within 14 days | Confirm the diagnosis; document the configuration and severity. |
| 2 | History and exam — focal neurology, otoscopy | Identify CHL vs SNHL; flag urgent neurological referral if focal signs present. |
| 3 | MRI with gadolinium (or ABR if MRI contraindicated) | Rule out vestibular schwannoma and other retrocochlear pathology.[2019] |
| 4 | Targeted serology only if indicated | Routine lab panels are not recommended per the 2019 guideline; specific tests where history justifies them. |
| 5 | ECochG (optional) | Only when atypical features raise specific hypotheses (hydropic onset, third window). |
FCase 8.1 — abrupt unilateral SNHL
What is the most appropriate next test according to the 2019 AAO-HNSF guideline?