A 58-year-old man visited his doctor concerned about a painful rash that developed over his neck and chest earlier that day. The patient mentioned that he was doing yard work and landscaping during the most sun-intense hours that day. On examination, violaceous, fine, scaly plaques in a photodistributed fashion were visible over his anterior neck and upper chest. When asked about medication history, he noted that he was currently on sulfamethoxazole and trimethoprim as treatment for urinary tract infections. The patient was otherwise well with no systemic symptoms.
What’s the diagnosis?
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