This girl has odd bumps on her arm, what's your diagnosis?
A 12 year old girl developed a few violet colored bumps on her upper, outer arm. Over several months, she developed more, in a linear pattern, moving down her arm. After about 1 year, the original bumps were starting to disappear, and it appeared that they were resolving in the order that they had appeared. They were mildly pruritic. The girl was otherwise healthy. No other family history of similar rashes.
What is your diagnosis?