Mycobacterium marinum infection
Well, since I asked for the classic story to go with such a presentation, I hoped most of you would hone in on the appearance, location and classic nature of the lesion. This is violaceous, on the dorsal hand, multicentric (which implies infection) and does not involve the entire dorsal hand, which shoots down PCT and its imitators. In my experience, pyoderma gangrenosum is more deep purple, is ulcerated and necrotic.
So, what's the classic story? She was cleaning her fish tank, (or working on her boat or scraping barnacles off her dock, etc. ) and got an abrasion; didn't think anything of it and a few weeks later she got these nodules on her hand.
Now, what's THIS lady's story? She doesn't remember anything at all. No trauma, no fish tank, no barnacles. But, she grew M. marinum, so who knows? Trust your eyes, not your ears!