A 27-year-old woman, gravida 1 para 0 at 30 weeks gestation, comes to the office due to increasing difficulty hearing, especially on the right side. She has had no ear pain or discharge. The patient has no prior medical conditions; the pregnancy has been uncomplicated other than an episode of acute cystitis 8 weeks ago, which was treated with antibiotics. She takes no medications aside from a multivitamin. The patient eats a balanced diet and does not use tobacco or alcohol. Vital signs are within normal limits. Bilateral tympanic membranes are normal with no middle ear effusion. A tuning fork held over the middle of the forehead sounds louder in the right ear. Tuning fork sounds are better heard with bone conduction on the right side and with air conduction on the left. The remainder of the neurologic examination shows no abnormalities. Which of the following is the most likely cause of this patient's current symptoms?
Interpretation of Rinne & Weber tests | ||
Rinne result | Weber result | |
Normal | AC > BC in both ears | Midline |
Conductive | BC > AC in affected ear, | Lateralizes to affected ear |
Sensorineural | AC > BC in both ears | Lateralizes to unaffected ear, |
Mixed | BC > AC in affected ear, | Lateralizes to unaffected ear, |
AC = air conduction; BC = bone conduction. | ||
Hearing loss is classified as either conductive (impaired transmission of sound to the inner ear) or sensorineural (involving the cochlea or auditory nerve), which can be distinguished with tuning fork examination. The Rinne test compares air conduction (tuning fork near the ear) versus bone conduction (tuning fork on the mastoid bone). With normal hearing, air-conducted sound is perceived as louder than bone-conducted sound. The Weber test is performed by placing the tuning fork on the middle of the forehead equidistant from both ears. The sound carried by bone conduction in this manner is normally heard equally in both ears; vibration heard louder in one ear is abnormal.
Conductive hearing loss can be caused by disorders of the external auditory canal (eg, cerumen impaction, otitis externa), tympanic membrane (eg, perforation), middle ear space (eg, otitis media, cholesteatoma), or the ossicular chain (eg, otosclerosis).
This young woman with conductive hearing loss and a normal otoscopic examination likely has otosclerosis. Otosclerosis results from an imbalance of bone resorption and deposition that leads to stiffening and ultimately fixation of the stapes, which dampens the transmission of sound energy from the tympanic membrane to the cochlea. Otosclerosis may progress during pregnancy. It is inherited in an autosomal dominant pattern with incomplete penetrance. Treatment involves hearing amplification or surgical reconstruction of the stapes.
(Choice A) Although chronic otitis media may cause conductive hearing loss, it is typically accompanied by ear pain and/or fullness, which were not reported by this patient. Examination of the tympanic membranes would show retraction of the tympanic membrane or fluid in the middle ear.
(Choice B) Aminoglycoside antibiotics can cause sensorineural (rather than conductive) hearing loss. In addition, they are more commonly used in pyelonephritis rather than cystitis.
(Choices C, E, and F) Although Ménière disease (episodic vertigo, fluctuating hearing loss), presbycusis (progressive hearing loss in advanced age), and vestibular schwannoma (CN VIII tumor) would all have normal otoscopic examinations, they would cause sensorineural hearing loss rather than conductive.
Educational objective:
Otosclerosis causes fixation of the stapes, which results in conductive hearing loss. It often presents in young women and may progress during pregnancy.