Stapedius — Acoustic Reflex Atlas
A printable compilation of the condition signatures, glossary and references. For the full narrative chapters, see the individual pages of the atlas.
The conditions at a glance
Otosclerosis
Stapes fixation — reflex absent on the probe side from the start
Decay: Decay testing is usually not interpretable because a reflex cannot be recorded on the affected side.
Audiogram: Right ear: low-frequency conductive loss with an air–bone gap and a Carhart notch around 2 kHz. Left ear normal.
Cochlear Hearing Loss
Sensorineural loss with recruitment — reflex at reduced sensation level
Decay: Reflex decay is normal (absent) in pure cochlear loss; abnormal decay points away from a cochlear site.
Audiogram: Symmetric mild-to-moderate sloping sensorineural loss with no air–bone gap.
Vestibular Schwannoma
Eighth-nerve tumour — elevated or absent reflexes with abnormal decay
Decay: Pathological reflex decay — amplitude falls to 50% or less of its initial value within 10 s at 500 or 1000 Hz — is a classic retrocochlear sign.
Audiogram: Right ear: asymmetric high-frequency sensorineural loss. Asymmetry is the cardinal audiometric clue.
Facial Nerve Palsy
Efferent-limb lesion — reflex absent on the probe side, lesion-dependent
Decay: Where the lesion is proximal to the stapedial branch, no reflex is recordable on the affected side, so decay cannot be assessed.
Audiogram: Hearing is typically normal — facial palsy does not affect the auditory pathway itself.
Intra-axial Brainstem Lesion
Crossed pathway interrupted — diagonal reflex pattern
Decay: Decay may be present and is variable; the crossed/uncrossed dissociation is the more reliable sign.
Audiogram: Hearing is often normal or near-normal — the lesion is central to the cochlea.
Conductive Hearing Loss
Middle-ear pathology — reflex blocked on the probe side
Decay: Not assessable on the affected side because no reflex can be recorded.
Audiogram: Right ear: flat conductive loss with an air–bone gap; bone conduction normal.
Auditory Neuropathy Spectrum Disorder
Dyssynchronous eighth-nerve transmission — reflexes absent, OAEs present
Decay: Reflexes are characteristically absent, so decay cannot be measured.
Audiogram: Variable audiogram — often a mild-to-moderate loss disproportionate to the very poor speech perception.
Ossicular Discontinuity
Disconnected ossicular chain — reflex absent, often a hypermobile tympanogram
Decay: Not assessable on the affected side.
Audiogram: Right ear: large conductive loss, often with a wide air–bone gap exceeding the loss seen in otosclerosis.
Otitis Media with Effusion
Middle-ear fluid — reflex absent on the probe side, type B tympanogram
Decay: Not assessable on the affected side, since a reflex cannot be recorded through an effusion.
Audiogram: Right ear: mild flat conductive loss with an air–bone gap; resolves as the effusion clears.
Tympanic Membrane Perforation
A hole in the eardrum — reflex absent on the probe side, large ear-canal volume
Decay: Not assessable on the affected side.
Audiogram: Right ear: conductive loss, its size depending on the perforation's size and location.
Multiple Sclerosis
Demyelinating brainstem disease — crossed reflexes affected, abnormal decay
Decay: Abnormal reflex decay can occur where demyelination affects the pathway; the crossed/uncrossed dissociation is the more characteristic sign.
Audiogram: Hearing is often normal or near-normal; the reflex abnormality is disproportionate to the audiogram.
Patulous Eustachian Tube
An abnormally open tube — breathing-synchronous admittance fluctuation
Decay: Decay is not the relevant measure here; the diagnostic feature is the breathing-synchronous baseline fluctuation rather than a true reflex abnormality.
Audiogram: Hearing is typically normal; symptoms are dominated by autophony rather than hearing loss.
Cerebellopontine-angle Meningioma
A non-schwannoma CPA mass — afferent compression, often with decay
Decay: Abnormal reflex decay may be present where the eighth nerve is compressed; findings overlap with vestibular schwannoma.
Audiogram: Right ear: asymmetric high-frequency sensorineural loss — asymmetry is again the audiometric clue.
Myasthenia Gravis
Neuromuscular-junction fatigue — a reflex that cannot be sustained
Decay: Fatigable reflex decay is the characteristic finding — the reflex weakens during the sustained tone as the neuromuscular junction fails, and may recover after rest.
Audiogram: Hearing is typically normal — myasthenia affects the muscle's neuromuscular junction, not the auditory pathway.
Hyperacusis
Reduced loudness tolerance — reflexes typically present, sometimes at lower levels
Decay: Decay is normal; hyperacusis is a disorder of loudness perception rather than of reflex sustainability.
Audiogram: Pure-tone hearing is characteristically normal — the difficulty is loudness tolerance, not sensitivity.
Bell's Palsy — Serial Monitoring
Tracking facial nerve recovery — the reflex returns as the nerve recovers
Decay: Once a reflex can again be recorded on the recovering side, decay can be assessed; during the absent phase it cannot.
Audiogram: Hearing is typically normal — the auditory pathway is unaffected.
Glossary
- Acoustic reflex
- The involuntary contraction of the stapedius muscle in response to a moderate-to-loud sound, measured clinically as a transient reduction in middle-ear admittance.
- Acoustic reflex arc
- The neural circuit underpinning the reflex: cochlea, eighth nerve, cochlear nucleus, superior olivary complex, facial nerve nucleus, facial nerve, and stapedius muscle.
- Acoustic reflex threshold (ART)
- The lowest stimulus level that produces a criterion admittance change (commonly 0.02 mmho). Normal tonal ARTs lie roughly 70–100 dB HL.
- Admittance
- A measure of how readily acoustic energy flows into the middle ear. Stapedius contraction reduces admittance; the recorded dip is the acoustic reflex.
- Afferent limb
- The incoming part of the reflex arc — cochlea and eighth nerve carrying the signal to the brainstem. A lesion here produces a stimulus-ear pattern.
- Crossed (contralateral) pathway
- Reflex pathways that cross the brainstem midline drive the contralateral reflex; uncrossed pathways drive the ipsilateral reflex. The distinction localises brainstem lesions.
- Diagonal pattern
- Crossed (contralateral) reflexes abnormal with uncrossed (ipsilateral) reflexes preserved. The signature of an intra-axial brainstem lesion.
- Efferent limb
- The outgoing part of the reflex arc — facial nerve carrying the motor command to the stapedius. A lesion here produces a probe-ear pattern.
- Metz test
- A reflex threshold appearing within 60 dB of the pure-tone threshold (reduced sensation level) indicates loudness recruitment and supports a cochlear site of lesion.
- Ossicular chain
- The malleus, incus and stapes, which transmit sound from the eardrum to the cochlea. Stapedius contraction stiffens this chain.
- Probe-ear pattern
- Reflexes absent for both conditions recorded with the probe in one ear. Points to a lesion of that probe ear — conductive or efferent (facial nerve).
- Recruitment
- An abnormally rapid growth of loudness with increasing intensity, typical of cochlear hearing loss. It underlies the reduced sensation level of the reflex in cochlear ears.
- Reflex decay
- Weakening of the reflex during a sustained 10-second tone. A drop to 50% or less of the initial amplitude at 500 or 1000 Hz is a positive (abnormal) result suggesting a retrocochlear lesion.
- Retrocochlear
- Relating to a site of lesion central to the cochlea — typically the eighth nerve or brainstem. Reflex decay and the stimulus-ear pattern are retrocochlear signs.
- Sensation level (SL)
- The level of a sound expressed in dB above an individual's threshold for that sound. Reflex decay is tested at 10 dB SL re: the reflex threshold.
- Stapedius muscle
- The smallest skeletal muscle in the body, attaching to the neck of the stapes. Its contraction stiffens the ossicular chain. Innervated by the stapedial branch of the facial nerve.
- Stimulus-ear pattern
- Reflexes abnormal whenever one ear is the stimulus, regardless of probe position. Points to an afferent-limb (cochlear or eighth-nerve) lesion.
- Tympanometry
- Measurement of middle-ear admittance as ear-canal pressure is varied. The companion immittance test to the acoustic reflex; type Ad is hypermobile, type As shallow, type B flat.
References
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- Møller AR (1962). Acoustic reflex in man. Journal of the Acoustical Society of America, 34(9), 1524–1534.
- Jerger S, Jerger J (1977). Diagnostic value of crossed versus uncrossed acoustic reflexes: Eighth nerve and brainstem disorders. Archives of Otolaryngology, 103(8), 445–453.
- Jerger J, Jerger S, Hall JW (1979). A new acoustic reflex pattern. Archives of Otolaryngology, 105(1), 24–28.
- Silman S, Gelfand SA (1981). The relationship between magnitude of hearing loss and acoustic reflex threshold levels. Journal of Speech and Hearing Disorders, 46(3), 312–316.
- Gelfand SA, Schwander T, Silman S (1990). Acoustic reflex thresholds in normal and cochlear-impaired ears: Effects of no-response rates on 90th percentiles in a large sample. Journal of Speech and Hearing Disorders, 55(2), 198–205.
- Anderson H, Barr B, Wedenberg E (1970). Early diagnosis of eighth-nerve tumours by acoustic reflex tests. Acta Oto-Laryngologica, Suppl. 263, 232–237.
- Hall JW (2014). Introduction to Audiology Today. Pearson, Boston.
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- Musiek FE, Baran JA (2007). The Auditory System: Anatomy, Physiology and Clinical Correlates. Pearson, Allyn & Bacon, Boston.
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- Metz O (1952). Threshold of reflex contractions of muscles of middle ear and recruitment of loudness. Archives of Otolaryngology, 55(5), 536–543.
- Hannley M, Jerger JF, Rivera VM (1983). Relationships among auditory brainstem responses, masking level differences and the acoustic reflex in multiple sclerosis. Audiology, 22(1), 20–33.
- Fowler CG, Wilson RH (1985). Adaptation of the acoustic reflex. Ear and Hearing, 6(5), 263–268.
- Gelfand SA (2009). Essentials of Audiology. Thieme, 3rd edition.
- Henry DF, DiBartolomeo JR (1993). Patulous Eustachian tube identification using tympanometry. Journal of the American Academy of Audiology, 4(1), 53–57.
- Blevins NH, Karmody CS (2003). Chronic myringitis: prevalence, presentation, and natural history. Otology & Neurotology, 24(1), 3–10.
- Warren RL, Gutmann L, Cody RC, Flowers P, Segal AT (1977). Stapedius reflex decay in myasthenia gravis. Archives of Neurology, 34(8), 496–497.
- Baguley DM (2003). Hyperacusis. Journal of the Royal Society of Medicine, 96(12), 582–585.
- Mangham CA, Carberry PH, Brackmann DE (1980). Management of intratemporal vascular tumors and the acoustic reflex in facial nerve disorders. Laryngoscope, 90(11), 1813–1819.