A man presents with vesicles over external acoustic meatus with ipsilateral facial palsy of LMN type. The cause is
**Core Concept**
The patient's symptoms suggest a diagnosis of Ramsay Hunt syndrome type 2, which is characterized by a herpes zoster infection of the geniculate ganglion, leading to vesicles over the external acoustic meatus and ipsilateral facial nerve palsy.
**Why the Correct Answer is Right**
The herpes zoster virus infects the geniculate ganglion, causing inflammation and damage to the facial nerve (cranial nerve VII). This results in a lower motor neuron (LMN) type facial palsy, characterized by weakness or paralysis of the muscles of facial expression, including the orbicularis oculi, orbicularis oris, and others. The presence of vesicles over the external acoustic meatus is a classic sign of Ramsay Hunt syndrome type 2.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately describe the clinical presentation of Ramsay Hunt syndrome type 2. While herpes zoster can cause facial palsy, it typically occurs in the context of a rash on the face, not vesicles over the external acoustic meatus.
**Option B:** This option is incorrect because it suggests a different diagnosis, such as Bell's palsy, which is an idiopathic facial palsy without a rash or vesicles.
**Option C:** This option is incorrect because it is not a specific diagnosis and does not accurately describe the clinical presentation of Ramsay Hunt syndrome type 2.
**Clinical Pearl / High-Yield Fact**
Ramsay Hunt syndrome type 2 is a classic example of a herpes zoster infection affecting a cranial nerve, and it is essential to consider this diagnosis in patients with facial palsy and a rash over the external acoustic meatus.
**Correct Answer: D. Herpes zoster infection of the geniculate ganglion**