My husband grew this from a package of tomato seeds, is confused by it looking like Frankenstein's monster, and wants to know if it is even a tomato and why it looks like this.
My guess is that it's a genetic dud, with how the lower stem is swelling significantly in the center and there is no proper growth tip forming. There is energy going up but it can't extend. I see stuff like this occasionally too, its usually pretty random. Some times two starter leaves grow and nothing forms between them, I see it in beans as well as toms. I would tend to think the seedling is perishing because its simply unable to grow with those genetics.