One of the "crossover" diagnostic groups that doesn't get much press is the crossovers between Giftedness (especially profound giftedness) and both ADD and the Autism Spectrum Disorders.
For a concrete example, check out these articles:
Notice that both mention "He is soooo sensitive and feels other people’s pain as his own."
It turns out that a lot of the things people noticed about Caleb that they labeled either ADD/ADHD or Asperger's Syndrome are also things that are part of the diagnostic criteria for gifted kids (like hypersensitivity, a tendency to get overstimulated, a slight-to-massive disconnect with age-peers, a tendency to get fixated on something, an over-attention to some details but inability to see others, etc).
It MAY BE that those things cross over because giftedness includes disorders. But Fibromyalgia doesn't include ADD necessarily.
We could compare it to an itch. Say I have an overwhelming urge to scratch my arm. You could say, "You have a mosquito bite." And, in fact, I might. But I also might have a healing sunburn, chicken pox, a cancerous mole, a spider bite, poison ivy, eczema, an allergy to strawberries, a random itchy spot, dry skin, sympathy pains for someone who is itchy, been exposed to itching powder, or any number of other things.
And while many of these might be relieved temporarily by hydrocortisone cream, some respond better to benadryl, and some to calamine, and some to scratching! Treating them all the same is not only a mistake, it can be counter-productive or even harmful.
It's a mistake to attribute all similar symptoms to one disorder.
Also, suppose, for example, that Asperger's syndrome has been inappropriately grouped with the Autism Spectrum disorders...suppose it actually belongs on a "Giftedness spectrum". Would we consider it differently? Would we treat it differently? Would we give Aspie's different respect and "breaks" in the world? You bet. The reality is that every "disorder" is just an extreme expression of a normal "order". So if you make "giftedness" a spectrum of order, isn't it possible that at some point you might move so far down that spectrum that it becomes a disorder, meaning it disrupts your ability to function in your world? And isn't it possible that the disruptions might express themselves in the same way that other disruptions do (like in an overfocus/inability to focus cycle of interest/boredom)?
Part of the problem here is that society has defined "gifted" as a desirable thing, and so they refuse to/cannot see what challenges are associated with it, and if you try to do research or talk about it, the common response is either that you're bragging, or that you should "stop whining because you have what I want" (kind of the same response you might have if a self-made billionaire complained about the outlandish taxes he has to pay, or the unrealistic social expectations, or his struggles to maintain privacy and safety--you would have very little sympathy because he has something considered highly desirable in our society; like if a supermodel complains about the beauty regimen she has to go through. Tough beans, right?). The idea is "it's tough being perfect, isn't it"
There is very little research on these things--we either want to label a person "normal" (like me), "handicapped" ("not as good as me, even if they have a gift for financial genius") or "gifted" (superior than me so obviously their challenges are just them whining or grandstanding) without being able to see the whole picture accurately.
I guess if a "disorder" is defined by the diagnostic criteria, then gifted people DO have ADD, Asperger's, or whatever. But if a "disorder" is defined by its cause, even if the treatments cross over...then we have things pretty messed up.
So is it appropriate to treat some giftedness disruptions? I suppose so--if ritalin helps the profoundly gifted brain finish projects and not say inappropriate things, is that helpful? SURE. But wouldn't it be MORE helpful if we first properly identify what's going on first?
So, some links to peruse if this interests you: