Electrocochleography in children with auditory synaptopathy/ neuropathy: Diagnostic findings and characteristic parameters

Introduction: The early diagnosis of AS/AN in children remains challenging because it exclusively relies
on the detection of OAE and/or CM, while ABR are pathologically changed or missing.
The aim of our study was to ensure the diagnosis of AS/AN, demarcate it to an outer hair cell damage
and possibly differentiate between pre- and postsynaptic pathologies.
Methods: We retrospectively evaluated the transtympanic ECochG results of ten children with AS/AN
and compared them to a matched group with SNHL and without any signs of AS/AN. We analyzed the
thresholds, latencies and – as a new parameter – the amplitude ratio between CAP and SP.
Results: CM and SP thresholds were significantly lower than CAP thresholds in AS/AN patients and
significantly lower than SP and CM thresholds in SNHL patients with comparable CAP thresholds. The
CAP/SP ratio of amplitudes in SNHL children was more than three times (significantly) higher than in AS/
AN children. The cutoff value was set at 1.0 in order to differentiate between both groups with a 80–90%
sensitivity and specifity.
It was not possible to differentiate between a pre- and postsynaptic type of AS/AN in our collective.
Summary and conclusion: The ECochG can add valuable information for a precise differential diagnosis of
AS/AN, especially in babyhood. We identified the CAP/SP ratio as a new parameter for differentiation
between AS/AN and SNHL. When the CAP/SP ratio falls below 1.0, patients can be diagnosed AS/AN with
high specificity and sensitivity. Significantly smaller SPL are needed to evoke SP and CM in the AS/AN
group, thus showing the preserved hair cell function.