An ECOG test (electrocochleography) is a 30-minute hearing test that measures the electrical activity of your inner ear and auditory nerve. It’s most commonly used to help diagnose Ménière’s disease and a related condition called endolymphatic hydrops, where excess fluid builds up inside the inner ear. Unlike a standard hearing test that checks what you can and can’t hear, an ECOG looks at how your inner ear generates electrical signals in response to sound.
Why Doctors Order an ECOG Test
The most common reason for an ECOG is suspected Ménière’s disease, a condition defined by four hallmark symptoms: fluctuating hearing loss, ringing in the ears (tinnitus), a feeling of pressure or fullness in the ear, and episodes of vertigo. These symptoms overlap with many other conditions, which makes Ménière’s difficult to diagnose on its own. The ECOG gives your doctor an objective measurement to work with rather than relying solely on your description of symptoms.
Specifically, the test looks for signs of endolymphatic hydrops, the excess fluid buildup that is thought to drive Ménière’s symptoms. In a survey of ear specialists who use the test, nearly 90% said their primary reason for ordering it was to determine whether hydrops is present. ECOG is also used during cochlear implant surgery to monitor inner ear function in real time as the electrode is being inserted.
What the Test Measures
The ECOG captures three main electrical signals produced by your inner ear when it receives sound:
- Cochlear microphonic (CM): An electrical signal generated by the tiny hair cells inside the cochlea. Its waveform mirrors the sound stimulus itself, almost like the ear producing an electrical copy of the incoming sound.
- Summating potential (SP): A steady electrical shift created by the vibration of the basilar membrane, a structure deep inside the cochlea that sorts sound by frequency.
- Action potential (AP): The combined firing of auditory nerve fibers as they respond to the sound. This represents the point where the signal leaves the inner ear and heads toward the brain.
The key number your audiologist looks at is the ratio between the summating potential and the action potential, called the SP/AP ratio. In a healthy ear, this ratio typically stays below about 0.35. When the ratio rises above that threshold, it suggests abnormal fluid pressure inside the cochlea, pointing toward endolymphatic hydrops.
What Happens During the Test
The test takes roughly 30 minutes. You’ll have small electrodes placed on your scalp and in or near your ear canal. There are two main approaches to electrode placement, and which one you experience depends on your clinic.
The more common version, called extratympanic, places the electrode on the skin of the ear canal or on the eardrum’s surface. This is noninvasive and painless, though you may feel mild pressure. The other approach, called transtympanic, passes a thin needle electrode through the eardrum to sit closer to the cochlea. This version produces stronger, cleaner signals but is more uncomfortable and less widely used outside of specialized centers.
Both methods produce reliable threshold measurements. Research comparing the two in the same ears found that while the transtympanic approach picks up larger signal amplitudes, both techniques detect the same thresholds and produce similar patterns. For most diagnostic purposes, the noninvasive version works well.
Once the electrodes are in place, you’ll hear a series of clicks or tone bursts through an earphone. You don’t need to press any buttons or respond. The equipment records your inner ear’s electrical responses automatically. You simply sit or lie still and stay as relaxed as possible, since muscle movement can interfere with the recording.
Understanding Your Results
The central finding on an ECOG report is the SP/AP amplitude ratio. Normal values in one large normative study ranged from about 0.08 to 0.36, with the upper cutoff at the 95th percentile set at 0.356. A ratio above that range is considered abnormal and suggests endolymphatic hydrops.
Your audiologist may also look at the SP/AP area ratio, which measures the same relationship but accounts for the full shape of the waveforms rather than just their peak heights. Normal area ratios run higher, up to about 1.67. Results exceeding either threshold are flagged as abnormal.
An abnormal result doesn’t automatically mean you have Ménière’s disease. The ECOG is one piece of a larger diagnostic picture that includes your symptom history, standard hearing tests, and sometimes imaging. Similarly, a normal ECOG doesn’t completely rule out Ménière’s, because the fluid buildup can fluctuate. If your test was done during a quiet period between episodes, the results may appear normal even though hydrops is present at other times. Some clinicians will repeat the test or order it specifically when symptoms are active to improve its accuracy.
ECOG vs. Other Hearing Tests
A standard audiogram measures the quietest sounds you can hear across different frequencies. It tells your doctor what your hearing loss looks like but not why it’s happening. An ECOG goes deeper, measuring the electrical behavior of the structures that produce hearing in the first place.
Another test you may encounter alongside ECOG is the auditory brainstem response (ABR), which tracks electrical signals as they travel from the ear up through the brainstem. While ABR is useful for diagnosing nerve-related hearing problems and acoustic neuromas, it doesn’t capture the cochlear-level detail that ECOG provides. For suspected Ménière’s or hydrops, ECOG is the more targeted tool.
Your doctor may order several of these tests together to build a complete picture. Each one examines a different part of the hearing pathway, from the fluid-filled cochlea to the auditory nerve to the brainstem relay stations that process sound before it reaches your brain.