<s>[INST] context: A painful vesicular rash in a dermatomal distribution strongly suggests herpes zoster, although other viral pathogens may also cause vesicles. Herpes zoster may involve the eyelid when the first or second branch of the fifth cranial nerve is affected. Prompt treatment with an antiviral such as acyclovir, valacyclovir, or famciclovir shortens symptomatic illness and decreases the chance of post-zoster neuralgia. Impetigo is a cellulitis caused by group A-hemolytic streptococci. It often involves the face and can occur after an abrasion of the skin. Its distribution is not dermatomal, and it rarely causes severe pain. Chickenpox produces vesicles in various stages of development that are diffuse and produce more pruritus than pain. Coxsackievirus can produce a morbilliform vesiculopustular rash, often with a haemorrhagic component and with lesions of the throat, palms, and soles. Herpes simplex virus (HSV) causes lesions of the lip (herpes labialis) but does not spread in a dermatomal pattern. [/INST] question: An 80-year-old female patient complains of a 3-day history of a painful rash extending over the right half of her forehead and down to her right eyelid. There are weeping vesicular lesions on physical examination. Which of the following is the most likely diagnosis? | options: A: Impetigo B: Adult chickenpox C: Herpes zoster D: Coxsackie A virus | answer: C </s>