The Test That Detects Hearing Loss Missed by Doctors

Imagine facing challenges in understanding conversations in a bustling restaurant or staying on track in a busy office, only to be informed by a doctor that your hearing is normal. This is the frustrating situation for individuals with cochlear synaptopathy, also known as hidden hearing loss.

According to the Hearing Health Forum EU, approximately 34 million adults in the EU experience disabling hearing loss. However, the actual magnitude of the issue is likely much larger, as standard hearing tests cannot identify cochlear synaptopathy.

This condition lacks a clinical diagnosis and an approved treatment, leaving many with genuine hearing challenges without assistance.

Hidden hearing loss can be debilitating, as explained by Professor Ingeborg Dhooge, head of the Ear, Nose, and Throat department at Ghent University Hospital in Belgium. Dhooge was a clinical consultant for a research initiative called EarDiTech, which studied the condition from 2022 to 2026.

The project received funding from the European Innovation Council, which supports transforming bold scientific ideas into practical solutions.

“Everywhere you go, there is always noise,” Dhooge said. “When shopping, there is noise, music playing. At work, open plan offices create background noise, affecting patients’ productivity.”

Current options involve training people to lip read and focus on speech sounds. However, the EarDiTech researchers developed a test to detect hidden hearing loss and are working on innovative software for hearing aids.

The Mechanism of Hearing Impairment

In the inner ear, sound is detected by tiny hair cells that transform vibrations into neural signals, which travel to the brain via synaptic connections between hair cells and the auditory nerve.

It was previously believed that age-related hearing loss begins with damaged hair cells.

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To some extent, hearing aids can help, but it’s difficult because with them everything becomes louder, but not necessarily clearer.

“We now know that the first damage to auditory structures is not the hair cells, but actually the synapses connecting hair cells to the brain,” explained Professor Sarah Verhulst, head of the Hearing Technology lab at Ghent University.

This distinction is crucial, emphasized Verhulst, as the EarDiTech research coordinator. One synapse per hair cell is sufficient to detect sound, but multiple synapses are needed to interpret speech in noisy environments.

The audiogram is the standard tool for assessing hearing, where patients respond to tones at various pitches and volumes. It assesses hair cell performance but does not reveal the number of working synapses, thus missing the difficulties of those with cochlear synaptopathy.

Assessing Synapses

The EarDiTech test combines electrodes placed on the forehead and earlobes with a specially designed audio stimulus, developed through years of auditory system modeling research.

“We built computer models of the hair cells and synapses,” Verhulst said. “We can simulate auditory nerve responses or synapse responses in the whole cochlear model. Using this method, we identify the audio stimulus that best triggers all synapses simultaneously.”

The test aims to elicit the strongest synaptic response. When someone with healthy synapses hears the stimulus, electrodes detect a significant spike in neural activity. In individuals with synapse loss, the response is smaller.

“By comparing the size of a patient’s response to a normal hearing response, we estimate the degree of cochlear synaptopathy,” Verhulst said.

The researchers have miniaturized the technology into a compact, portable device. Clinical trials at Ghent University demonstrate its ability to identify cochlear synaptopathy across various age groups.

The test is simple and non-invasive, easily integrated into everyday clinical practice, providing audiologists and ENT specialists with a previously unavailable tool.

The next step is obtaining CE marking