Characteristics in SP and AP measured by EcochG in normal-hearing adults: significance for auditory degeneration and hidden hearing loss detection

BACKGROUND: Age-related and hidden hearing loss (HHL) can develop despite normal audiometric thresholds, reflecting neural degeneration undetectable by standard tests. Electrocochleography (ECochG) enables direct assessment of cochlear and neural function. OBJECTIVE: To investigate age-related changes in ECochG waveform components, specifically the summating potential (SP) and compound action potential (AP), in individuals with normal hearing thresholds, and to evaluate their significance in identifying auditory degeneration and HHL. MATERIAL AND METHODS: Sixty-four participants (128 ears) aged 10-69 years with normal hearing (≤25 dB HL, 0.5-4 kHz) underwent transtympanic ECochG using 80 dB nHL click stimuli. SP and AP latencies, amplitudes, SP/AP ratio, and AP-SP amplitude were analyzed using Spearman correlation and Kruskal-Wallis tests. RESULTS: SP and AP amplitudes and AP-SP amplitude decreased significantly with age (p < 0.05), while AP latency increased (p < 0.05). SP latency and SP/AP ratio showed no significant age-related changes. The 60-69-year group demonstrated the greatest declines. CONCLUSIONS AND SIGNIFICANCE: ECochG detects age-related reductions in cochlear and auditory nerve responses in normal-hearing individuals, supporting its utility as a sensitive electrophysiological marker of early auditory neural degeneration and HHL.