Paralysis of which muscle lead to hyperacusis in Bell’s palsy: September 2008
**Core Concept**
Bell's palsy is a peripheral seventh cranial nerve (facial nerve) palsy that results in unilateral facial paralysis, including weakness or paralysis of the muscles of facial expression. The facial nerve is responsible for motor innervation of the muscles of facial expression, as well as sensory innervation of the external auditory meatus and taste sensation from the anterior two-thirds of the tongue.
**Why the Correct Answer is Right**
Hyperacusis, or an increased sensitivity to sound, is a common symptom of Bell's palsy. This occurs due to paralysis of the stapedius muscle, which is one of the smallest muscles in the human body. The stapedius muscle is innervated by the facial nerve and plays a crucial role in regulating sound by contracting and relaxing to modulate the movement of the stapes bone in the middle ear. When the facial nerve is paralyzed, the stapedius muscle cannot contract, leading to an inability to dampen loud sounds, resulting in hyperacusis.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because paralysis of the orbicularis oculi muscle would lead to difficulty closing the eye, not hyperacusis.
**Option B:** This option is incorrect because paralysis of the platysma muscle would lead to weakness in the anterior neck muscles, not hyperacusis.
**Option C:** This option is incorrect because paralysis of the masseter muscle would lead to weakness in mastication, not hyperacusis.
**Clinical Pearl / High-Yield Fact**
The stapedius muscle is the smallest skeletal muscle in the human body, and its paralysis can lead to significant hearing-related symptoms, such as hyperacusis.
**Correct Answer: C. Masseter muscle paralysis would lead to weakness in mastication, not hyperacusis. However, the correct answer is actually D. Stapedius muscle paralysis.