Neurology electrophysiology · Patient guide
Brainstem auditory evoked potentials, the neurological BAEP — testing brainstem conduction in MS, coma and posterior fossa disease.
The BAEP records the electrical response of the auditory brainstem pathway to click stimuli. Used in neurology to assess brainstem conduction — multiple sclerosis, brainstem lesions, coma prognosis and intra-operative monitoring in posterior-fossa surgery.
Key facts
- 01
Definition
A neurology-clinic electrophysiological test of the brainstem auditory pathway, recorded from the scalp in response to click stimuli.
- 02
Same technique as ABR
The recording is identical to an audiology ABR — but interpreted neurologically, framed around brainstem conduction rather than hearing threshold.
- 03
Waves I to V
Wave I reflects the cochlear nerve; waves II–V track conduction up through pons and mid-brainstem to the inferior colliculus.
- 04
Prolonged interpeak intervals
A widened I–III or I–V interval suggests demyelination — a classic finding in multiple sclerosis.
- 05
Absent later waves
Absence of wave V (with wave I preserved) points to a lesion of the auditory brainstem pathway.
- 06
Intra-operative monitoring
Used in real time during vestibular schwannoma resection and posterior-fossa surgery to protect the auditory brainstem.
Preparation and procedure
What a BAEP appointment actually looks like — in order.
A relaxed, quiet recording — around 30 minutes on the couch, with a written report from a consultant clinical neurophysiologist to follow.
- 01
Before
Neurology consultation
A consultant neurologist reviews history, examination and imaging, and specifies the clinical question the BAEP is being asked to answer.
- 02
On the day
Skin prepared with gel
The scalp and mastoid areas are lightly abraded and cleaned with electrolyte gel to bring impedance down for a clean trace.
- 03
On the day
Surface electrodes applied
Small surface electrodes are placed on the vertex and on each mastoid — no needles, no discomfort.
- 04
On the day
Click stimuli via headphones
Brief click stimuli are delivered through insert earphones at a defined intensity and rate.
- 05
On the day
Left and right ears tested
Each ear is tested independently. Averaged responses are recorded to isolate the brainstem signal from background EEG.
- 06
On the day
Recording in a quiet room
You lie still and relaxed in a quiet, low-light room. The recording itself takes around 30 minutes.
- 07
After
Neurophysiology reporting
A consultant clinical neurophysiologist measures wave latencies and interpeak intervals, and issues a written neurological report.
What it shows
When a neurological BAEP is the right test.
BAEP answers a specific question — is the auditory brainstem pathway conducting normally, and if not, where and how badly. These are the presentations where it earns its place.
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Multiple sclerosis
Delayed I–V interpeak interval is a classic supportive finding for demyelinating disease in the brainstem.
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Brainstem lesion
Absent wave V with a preserved wave I localises to the auditory brainstem pathway above the cochlear nerve.
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Vestibular schwannoma
Asymmetric I–III interpeak intervals raise suspicion of a retrocochlear lesion — prompts MRI internal auditory meatus.
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Coma prognosis
Bilaterally absent wave V after cardiac arrest is a strong predictor of poor neurological outcome.
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Intra-operative monitoring
Real-time BAEP during posterior-fossa surgery gives the surgeon early warning of brainstem or VIII-nerve compromise.
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Ototoxicity screen
Serial BAEPs monitor for auditory pathway injury from platinum chemotherapy, aminoglycosides and other ototoxic drugs.
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Concussion and TBI monitoring
Adjunctive assessment of brainstem integrity after traumatic brain injury or repeated concussion.
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Red flag: bilaterally absent waves post-cardiac arrest
A poor prognostic sign — requires MDT discussion, not a stand-alone bedside decision.
After the report
What typically happens next.
BAEP rarely acts alone — the report feeds into a wider neurological pathway. These are the routes patients most often take.
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Neurology follow-up
The BAEP is one thread in the diagnosis — the consultant neurologist integrates it with history, examination and imaging.
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MRI brain / IAM
A confirmed abnormality is followed by MRI brain and dedicated internal auditory meatus sequences for structural correlation.
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Demyelinating-disease work-up
When MS is suspected, work-up extends to full MRI, CSF oligoclonal bands and visual evoked potentials.
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Neurosurgical referral
A space-occupying lesion — vestibular schwannoma, brainstem tumour, Chiari malformation — is referred to skull-base neurosurgery.
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ITU MDT for coma prognosis
Post-cardiac-arrest BAEPs are discussed within a multi-modal ITU prognostication MDT, never in isolation.
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Rehabilitation input
Neuro-rehabilitation is arranged where deficits are established, with input from PT, OT and SLT as needed.
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Auditory rehabilitation
Hearing aids and auditory rehabilitation are considered where cochlear or retrocochlear hearing loss is confirmed.
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Serial BAEPs
Follow-up recordings track progression in demyelinating disease, post-op recovery, or ototoxic drug exposure.
Red flags
When a BAEP finding demands escalation.
Some findings shift a BAEP from a diagnostic input into a trigger for urgent multidisciplinary review. These are the ones every neurophysiology report flags.
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Bilaterally absent waves post-cardiac arrest
Strongly associated with poor neurological outcome — requires urgent ITU MDT input.
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Rapid progression in MS
A sudden interval prolongation on serial BAEPs warrants urgent neurology review and MRI.
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Post-op brainstem stroke
New loss of waves after posterior-fossa surgery raises suspicion of brainstem infarction — urgent imaging.
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Ototoxic drug injury
New wave I abnormality on a monitoring BAEP is an early sign of ototoxicity — flag to oncology / pharmacy.
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Vestibular schwannoma with hearing loss
Asymmetric BAEP with sensorineural loss demands MRI IAM and skull-base referral.
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Chiari malformation with brainstem compression
Abnormal conduction in a symptomatic Chiari patient is a neurosurgical trigger.
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Central pontine myelinolysis
Rapid pontine wave loss in the right clinical context is a red flag for osmotic demyelination.
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Post-anoxic brain injury
Loss of later waves after hypoxic insult carries prognostic weight — MDT interpretation only.
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Locked-in syndrome differential
BAEPs help separate locked-in syndrome (waves preserved) from severe brainstem injury (waves lost).
Frequently asked
The questions patients ask about BAEP.
Quick answers on how BAEP differs from an audiology ABR, what it tells the neurologist, and how it reads in coma and MS.
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What is the difference between a BAEP and an ABR?
They are essentially the same recording — click stimuli, scalp electrodes, averaged auditory brainstem response. The audiology ABR is interpreted around hearing threshold; the neurology BAEP is interpreted around brainstem conduction — latencies, interpeak intervals and wave morphology in the context of MS, brainstem lesions and coma prognosis.
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Does a BAEP diagnose multiple sclerosis on its own?
No. A prolonged I–V interpeak interval is supportive of a demyelinating brainstem lesion, but the diagnosis of MS is made by a neurologist using clinical criteria, MRI and — where needed — CSF analysis. BAEP is one piece of that picture.
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Is the test painful?
No. Surface electrodes and click stimuli through headphones — no needles, no radiation, no discomfort. The main requirement is to lie still and relaxed in a quiet room for around half an hour.
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Why is BAEP used in coma?
The brainstem is anatomically deep and hard to examine at the bedside. BAEP provides an objective measure of brainstem conduction. Bilaterally absent wave V after cardiac arrest, alongside other multi-modal signals, is one of the strongest predictors of poor neurological outcome.
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What does intra-operative BAEP monitoring do?
During vestibular schwannoma resection or other posterior-fossa surgery, continuous BAEP gives the surgeon real-time warning if the auditory brainstem pathway is under mechanical or vascular stress — so surgical strategy can be adjusted before injury becomes permanent.
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How long does it take to get a report?
The written neurophysiology report is typically issued within a few working days. Urgent inpatient and ITU cases — coma prognostication, post-op monitoring — are reported the same day.
Sources
Guidelines and professional bodies.
This patient guide draws on standards from the leading UK, European and US clinical neurophysiology bodies. Next review 2027-07-30.
Related tests
Looking for a different test?
-
Auditory brainstem response (ABR)
The audiology-clinic version of the same recording — read for hearing threshold rather than brainstem conduction.
Learn more -
MRI brain
The structural gold standard for demyelination, brainstem lesions and posterior-fossa pathology.
Learn more -
Acoustic reflex threshold
A middle-ear reflex test that complements BAEP in localising auditory pathway disease.
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In practice, in London
How brainstem auditory evoked potentials tends to unfold when you go private
With brainstem auditory evoked potentials, the London question is usually about report turnaround and the radiologist reading it — not whether the scan is available. The wait for brainstem auditory evoked potentials on the NHS depends heavily on where you live and how urgently the referral is graded. Central and West London private clinics can normally book within a week, with imaging or a procedure slot to follow shortly after. It’s worth being honest about the reason for going private: usually it’s time, not a fundamentally different test.
Once you’re in the private system for brainstem auditory evoked potentials, the pace picks up noticeably. Consultant slots run to time, imaging is usually available in the same building or a short walk away, and the report comes back typed and detailed. It’s the coordination that tends to feel different — one person on the other end of the phone, not a switchboard. For brainstem auditory evoked potentials specifically, the difference between a routine report and a sub-speciality read is where private care earns its keep.
Fit matters more than people expect. For brainstem auditory evoked potentials, the right consultant depends on what you actually need — a second opinion, a definitive diagnosis, a bridge into treatment, or reassurance that nothing’s being missed. We match on that, not on who has the biggest brochure. If a test isn’t the right next step, we’ll say so before you book anything.
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