a 40-year-old man presents with a 3-day history of right-sided chest pain. it is gradually increasing in intensity, burning in character, and like a band across his mid-chest and mid-back on the right side. today, he noticed a light rash in this area; out of concern, he visited his doctor. he has no fever, but he is experiencing fatigue and malaise. his past medical history includes gerd, for which he is on lansoprazole daily; asthma, for which he uses albuterol inhaler daily; and knee arthritis, for which he uses over-the-counter low dose naproxen as needed. family history is noncontributory. on examination, he is afebrile with a bp of 128/80 mm hg and a pulse of 70 bpm. oral exam is unremarkable. lungs are clear, and the abdomen is benign. on the right side of his chest, there are small vesicles with surrounding erythema in the mid region. the skin is excruciatingly tender in a dermatomal fashion along the affected area. question: what is the most likely diagnosis?
