A 63-year-old male presents with a crusting vesicular rash on the right side of his face that does not cross the midline, along with limited mobility of facial muscles and tinnitus on the affected side. The diagnosis is Ramsay Hunt syndrome. Which nerve is most likely affected?

Correct answer: D. Facial nerve (CN VII)

• A. The trigeminal nerve (CN V) mediates facial sensation. While Ramsay Hunt syndrome can occasionally affect CN V (causing facial pain/neuralgia), it is not the primary nerve responsible for the facial muscle paralysis and vesicular eruption pattern described. The hallmark is facial motor involvement.
• B. The vestibulocochlear nerve (CN VIII) explains the tinnitus component of Ramsay Hunt syndrome, but it is the facial nerve (CN VII) that is PRIMARILY affected and responsible for the defining facial paralysis and vesicular eruption in this condition.
• C. The hypoglossal nerve (CN XII) controls tongue movement. It is not involved in Ramsay Hunt syndrome and does not explain facial paralysis or vesicular rash.
• D. CORRECT. Ramsay Hunt syndrome is caused by varicella-zoster virus (VZV) reactivation in the geniculate ganglion of the facial nerve (CN VII). This causes: (1) ipsilateral facial muscle paralysis/paresis (loss of facial movement), (2) vesicular eruption on the ear/face in the CN VII distribution, and (3) ipsilateral ear pain. Tinnitus and hearing loss can co-occur due to the proximity of CN VII and CN VIII at the geniculate ganglion.