A 40-year-old woman presents with painful vesicular lesions distributed on one side of her body. What is the most probable diagnosis?

Explanation

The patient's unilateral painful vesicular rash is characteristic of herpes zoster, which results from reactivation of the varicella-zoster virus. Chickenpox typically causes a generalized vesicular rash. Recurrent herpes simplex infections usually affect mucocutaneous areas rather than a dermatomal pattern. Infectious mononucleosis does not present with vesicular eruptions.