Disorders of Hearing and Audiologic Assessment
Types and configurations
Conductive loss involves outer/middle ear; sensorineural involves cochlea or retrocochlear pathway; mixed combines both. Air-bone gaps indicate conductive components. Asymmetry, poor word recognition, and rollover suggest retrocochlear pathology. Presbycusis is typically bilateral, high-frequency, sensorineural.
Assessment tools
Pure-tone audiometry establishes thresholds; speech audiometry measures recognition and the speech recognition threshold. Tympanometry classifies middle-ear status (Type A normal, B flat/effusion or perforation, C negative pressure). Acoustic reflexes assess the reflex arc (afferent cochlea → brainstem → efferent facial nerve). Otoacoustic emissions reflect outer hair cell function and are absent with significant sensorineural loss (>~30 dB HL). Auditory brainstem response evaluates retrocochlear integrity and estimates thresholds in difficult-to-test patients.
Traps
A common trap: assuming OAEs are present in all normal ears - they can be absent with even mild loss. Another: misreading tympanometry types. Also watch for confusing the speech recognition threshold (50% correct) with most comfortable level or uncomfortable level.
Rule of thumb
Air-bone gap >10 dB suggests conductive component; present OAEs imply cochlear outer hair cell function better than ~30 dB HL.