A 28-year-old patient comes to the office for evaluation of a rash. At first there was only one large patch, but then more lesions erupted suddenly on the back and torso; the lesions itch. On physical examination, you note that the pattern of eruption is like a Christmas tree and that there are a variety of erythematous papules and macules on the cleavage lines of the back. Based on this description, what is the most likely diagnosis?
Correct Answer: A
Rationale: The correct answer is A: Pityriasis rosea. The key features that point towards this diagnosis include the sudden eruption of lesions in a Christmas tree pattern on the back and torso, along with itching. Pityriasis rosea commonly presents with a single large patch followed by smaller lesions in a distinct pattern. Other choices can be ruled out based on the description provided. Tinea versicolor typically presents with hypo- or hyperpigmented patches, not the erythematous papules and macules described. Psoriasis usually presents with thick, silvery scales, not erythematous lesions in a Christmas tree pattern. Atopic eczema may present with erythematous papules, but the Christmas tree pattern and acute onset described are not typical.