AIIMS May 2007 MCQ ENT Answer 1

The Correct Answer is C

Otosclerosis is a primary disease of the otic capsule and the ossicles. It is not known to occur outside the human temporal bone. It is characterized by a progressive hearing loss that may be conductive, sensorineural, or mixed. Histologically, it is seen as abnormal resorption and then deposition of bone in the labyrinthine capsule and middle ear. Otosclerosis is an important cause of auditory and, to a lesser extent, vestibular symptoms, and both can be treated effectively in most cases.

The patient with otosclerosis typically presents with a history of slowly progressive hearing loss that is often bilateral and asymmetric. The hearing loss usually presents between the ages of 15 and 45. It occurs approximately twice as often in women than in men. In 70% of patients there is a family history of deafness. Younger patients often have a more rapid progression of the hearing loss. It is often rapidly progressive during pregnancy and in women on estrogen therapy.

Audiology

The key test in the diagnosis of otosclerosis remains the audiogram. The audiological manifestations of otosclerosis are as distinctive as they are varied. Characteristic abnormalities appear on tympanometry, acoustic reflexes, and the pure-tone audiogram.

The tympanogram is a graphic representation of the change in acceptance of sound energy through the middle ear as a function of air pressure.

• The most typical case is the presence of a normal, type A typanogram. As the disease progresses the height of the peak decreases and you can eventually obtain a type
  

  As

  tympanogram.

Acoustic reflex morphology is a very sensitive indicator of otosclerosis. In contrast to the normal configuration in which middle ear compliance is reduced for the duration of a stimulus, in otosclerois there is a characteristic diphasic response or “on-off” phenomenon. With this response there is an increase in compliance at both the onset and termination (“offset”) of the sound stimulus. Forty percent of the normal population can have a brief compliance increase at the onset of a stimulus but the offset increase (at the termination of the signal) is virtually pathognomonic of early stapedial fixation. It is often seen in the first 5 years of disease progression but is rarely seen in otosclerosis of 10 years or longer. This “on-off” response can often be seen prior to the development of a detectable air-bone gap. Advancing stapedial fixation affects both the ipsilateral and contralateral acoustic reflexes.

Pure tone audiometry is always a part of the assessment and a gradually progressive low-frequency conductive hearing loss is first seen. As the sclerosis worsens and the footplate becomes fixed, a mass effect is added to the audiogram. This results in a stabilization of low-frequency thresholds, with worsening in the high frequencies and a gradual widening of the air-bone gap. The configuration changes from upward sloping to flat. Complete stapes fixation will give a maximum conductive hearing loss of 60 to 65 dB HL as long as there is not progression of the disease to involve the cochlea. Usually though, there is development of cochlear otosclerosis, and the loss becomes mixed or sensorineural. High frequencies are more severely affected at this point.

The audiometric hallmark of stapes fixation is the Carhart notch, characterized by elevation of bone conduction thresholds of approximately 5 dB at 500 Hz, 10 dB at 1,000 Hz, 15 dB at 2,000 Hz, and 5 dB at 4,000 Hz. It is important to realize that the Carhart notch is a mechanical artifact, not a true representation of cochlear reserve. Commonly, one can obtain “overclosure” of the air-bone gap after stapedectomy with postoperative air-conduction thresholds lower than preoperative bone-conduction thresholds.

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