Stapedius Reflex Measurement

Stapedius reflex measurement is a non-invasive (non-penetrating into the body) ear, nose and throat medicine procedure for objective functional diagnosis of the conductive apparatus. Together with tympanometry (middle ear pressure measurement), it is a part of impedance change measurement. Due to the impedance (acoustic resistance) of the eardrum and middle ear, part of the sound energy supplied from the outside is not transmitted to the inner ear, but is reflected at the eardrum. The measurement procedure detects changes in impedance caused, among other things, by the stapedius reflex. The stapedius muscle contracts reflexively at high volumes, thereby stiffening the ossicular chain to protect the inner ear. Many diseases of the middle and inner ear as well as the reflex arc lead to deviating impedance values and are thus diagnosed with the help of the measurement. Because the procedure does not rely on patient compliance (in this case, cooperative behavior), it is ideally suited for neonatal/infant examination.

Indications (areas of application)

As a method of hearing assessment:

  • Objective hearing test method: to be used in children and non-cooperative patients. In the case of high-grade hearing loss of the insonated ear, the reflex remains absent because the reflex threshold is not reached.
  • Newborn screening
  • Fitting of hearing aids in childhood

If there is a question about conductive disorders (dysfunction of the middle ear):

  • Fixation of the ossicular chain in the case of:
  • Disruptions of the ossicular chain in:
    • Anvil dislocation (uncoupling) e.g. after fracture of petrous bone no stapedius reflex is detectable.

When asked about sound sensation disorders:

  • V. a. METZ recruitment: in the healthy ear, the outer hair cells act sound amplifying at low sound intensities and attenuating at high ones. In the case of sensory hearing loss (sensory cell dysfunction), both sound amplification and attenuation are lost. The result is, on the one hand, a hearing loss and, on the other hand, a disproportionately strong increase in loudness perception at sound levels above the hearing threshold (recruitment). When measured, the stapedius reflex threshold is pathologically (pathologically) close to the hearing threshold (eg 30 dB).
  • V. a. retrocochlear hearing loss (located behind the cochlea): if there is damage to the retrocochlear structures (eg, the auditory nerve), the stapedius reflex remains absent or the distance between hearing and reflex threshold increases.
  • V. a. Auditory fatigue: The afferent (feeding) limb of the auditory pathway is damaged. With continuous exposure to sound, one can thus observe a decrease in the stapedius reflex, which is called “reflex decay”.

Neurological issues (relating to neurology):

  • Facial paresis (paralysis of the facial nerve): it can be inferred the localization of the nerve damage. The stapedius reflex is absent when the facial interruption is anterior to the branch of the stapedius nerve (stapes nerve).
  • Central lesions (damage): brain tumors or cerebral hemorrhage can interrupt the central reflex arc, causing the stapedius reflex to fail.

Contraindications

  • Acute sensorineural hearing loss/tinnitus (ringing in the ears).
  • Tympanic membrane perforation: impedance measurement is not possible if the tympanic membrane is defective.
  • Malformations of the external auditory canal: Strongly deviating shapes of the external auditory canal can lead to the fact that a complete seal of the measuring probe becomes impossible and thus no correct values can be measured.

The procedure

The stapedius reflex leads to a movement of the eardrum (TMD = Tympanic Membrane Displacement) due to the stiffening of the ossicular chain. This movement can be registered as a change in volume in the external auditory canal by a measuring probe. Various diseases influence the occurrence of the reflex, so that diagnostic conclusions can be drawn about the integrity of the inner ear, the function of the central auditory pathway and the reflex arc as well as the condition of the ossicular chain. Examination Technique

  • Impedance change measurement is performed without direct eardrum contact and is therefore not considered painful or uncomfortable by most patients. In children, the measurement can also be performed during sleep.
  • The ear canal is closed absolutely airtight with a plug, which also contains a small speaker, a microphone and a tube for air supply/pressure adjustment. Since the stapedius reflex causes only a very small change in impedance of the eardrum, it is necessary to perform the measurement in the most optimal vibration range of the eardrum. Therefore, in most cases, tympanometry is performed beforehand to determine the point of maximum eardrum mobility. This is a concrete value of the air pressure in the external auditory canal, which is preset for the subsequent stapedius reflex measurement.
  • Sound stimuli of various frequencies (500 Hz, 1 kHz, 2 kHz, 4 kHz, broadband noise) are directed into the ear via the loudspeaker. At sufficient volume, the reflex response can be measured as TMD (Tympanic Membrane Displacement) with a latency of about 10 ms.
  • Furthermore, it should be noted that the stapedius reflex is consensual, i.e., it can always be registered in both ears, even if only one ear is stimulated. For convenience, one ear is usually sonicated using headphones and the stapedius reflex is measured in the contralateral ear (opposite ear). However, in some central lesions, it is inevitable to measure the ipsilateral (same-side) reflex, so that stimulation and conduction occur in the same ear.
  • During evaluation, attention is paid to the bilateral presence of the stapedius reflex or to the level of the stapedius reflex threshold. This is the minimum loudness required to elicit the reflex and should be 70-100 dB for normal findings. The results are usually presented graphically as impedance or compliance (here: compliance of the eardrum).

Possible complications

  • Patients with acute sensorineural hearing loss or acute tinnitus should not undergo stapedius reflex measurement because of the risk of additional inner ear damage from the high sound pressures.