The body dysmorphic disorder (BDD) is a hell of a condition. Essentially, your perception of yourself is twisted because of some neurological or psychological reason, so no matter what you do, you always feel "wrong". Like with other delusions, it's not about what you think but HOW you think: the thought process itself becomes distorted so that any facts and logic always leads to the same conclusions internally.
The trap is that body modification is a gradual process, and the person can feel some temporary gain from getting more and more cosmetic surgeries done, but eventually they reach the point where it starts to go obviously wrong, or they can't continue because it would kill them, so they hit a the wall and still don't feel any better. The only thing that keeps them happy is the constant change.
Dennis may well have found that becoming a tiger wasn't making him happy anymore, so the problem must have been something else. The body dysmorphia is still there - it just changes targets - so he probably attempted to change his gender as well, with predictable results when you take hormones that affect your mood.