Voluntary eardrum movement: a marker for tensor tympani contraction?

Hypothesis: Voluntary eardrum movement (VEM) and resultant tympanometric changes reflect tensor tympani (TT) contraction.

Background: TT contraction has been hypothesized to cause symptoms of aural fullness, tinnitus, clicking, and even vertigo despite the lack of understanding of how it functions or what causes it to contract. Identifying tympanometric changes unique to TT contraction can provide a diagnostic tool for identifying its role in pathologic conditions.

Methods: Various tympanometric measurements were performed on human subjects who could voluntarily move their eardrums. These were compared with similar tympanometric measurements performed on cadaveric temporal bones while manually tensing the TT and stapedius muscles individually.

Results: Eight subjects (14 ears) who could cause VEM were identified. Compared with baseline, VEM resulted in significantly decreased middle ear compliance (p < 0.01) and middle ear pressure (p < 0.01) measurements. The compliance changes seen with VEM were larger than those seen with acoustically stimulated stapedius contraction. Finally, the direction of compliance change with VEM was dependent on the pressure applied to the external auditory canal (EAC), with compliance increasing with positive EAC pressure. This was not seen with stapedius contraction. These findings were reproduced using the cadaveric temporal bone model: larger compliance changes with pull on TT as compared with stapedius with neutral EAC probe pressure; change in direction of compliance changes with varying EAC probe pressure with TT pull, not with stapedius pull.

Conclusion: TT contraction produces distinctive tympanometric findings that can be used to support its abnormal contraction in ears with symptoms compatible with TT syndrome.