A 34-year-old man comes to the clinic with a 3-week history of difficulty hearing. He finds it increasingly difficult to tolerate everyday sounds. He also complains of ear pain and often avoids public places as a result. The patient has no past medical history and takes no medications. Injury to which of the following cranial nerves is most likely responsible for his condition?

Question

A 34-year-old man comes to the clinic with a 3-week history of difficulty hearing.  He finds it increasingly difficult to tolerate everyday sounds.  He also complains of ear pain and often avoids public places as a result.  The patient has no past medical history and takes no medications.  Injury to which of the following cranial nerves is most likely responsible for his condition?

Quizplus · Accepted Answer

11ec160b_35aa_308e_9249_a50bd9f864e0_MD0001_00 The middle ear cavity contains 3 auditory ossicles (malleus, incus, and stapes) and 2 skeletal muscles (tensor tympani and stapedius) that participate in the transmission of sound from the tympanic membrane to the cochlea. The stapedius muscle arises from the wall of the tympanic cavity and inserts on the neck of the stapes. It is innervated by the stapedius nerve, a branch of the facial nerve (CN VII). The stapedius muscle functions to stabilize the stapes; paralysis of the muscle (secondary to an injury or lesion to the facial nerve) causes the stapes to oscillate more widely, producing hyperacusis. Patients will typically complain of increased sensitivity to everyday sounds (eg, shutting doors, ringing phones, traffic) and will often withdraw socially as a result. Treatment consists of retraining (or sound) therapy using broadband noise (eg, "white noise"). The tensor tympani muscle arises from the cartilaginous portion of the auditory tube and the adjoining part of the sphenoid bone and inserts into the malleus. It functions to contract the tympanic membrane medially, thereby increasing its tension and dampening sound transmission. It is innervated by the mandibular branch of the trigeminal nerve (CN V₃). Ipsilateral hyperacusis is a common finding associated with Bell's palsy (unilateral/peripheral facial paralysis). (Choices A, C, D, and E) The accessory (CN XI), glossopharyngeal (CN IX), hypoglossal (CN XII), and vagus (CN X) nerves are not associated with hyperacusis. Educational objective: The stapedius muscle is innervated by the stapedius nerve (a branch of the facial nerve). Paralysis of the stapedius muscle results in hyperacusis (eg, increased sensitivity to sound).

A 34-Year-Old Man Comes to the Clinic with a 3-Week