Q:  I have ADHD the combined type and Bipolar One the manic type. Why is there no information about these comorbid diseases as a single pathology?

That, Jeff, is an outstanding question.  I think you're way ahead of most psychiatrists I've heard speak on this; in fact I've never heard anyone wonder aloud about whether these two diagnoses are actually one thing in some way, at least in some people.  At minimum I can tell you that several patients of mine had "ADD" diagnoses and were on stimulants, but after treatment for their mood instability they did not seem to need stimulants anymore.  However, several others (and I can't see what makes one of these folks different from the others) whose stimulants I stopped out of a concern about creating more mood instability did not do as well in terms of concentration until I put the stimulant back in.  On the other hand, this is a very small number of folks and I'm still not convinced it's really safe to take a stimulant for focus and concentration if you have bipolar disorder. 

There are probably some ADD specialists out there who would not appreciate hearing me talk like that.  On the other hand, there's Fredrick Goodwin, former head of NIMH, who said (paraphrasing) "I'd much rather call someone bipolar and be wrong than call someone ADD and be wrong, treat them with stimulants, and risk making their bipolar disorder worse" -- so at least that well-known authority shares my concerns. 

Anyway, the question about "co-morbidity" versus "a single pathology" is definitely a wise one, but I've not seen any writing on this either.  It's frustrating to me too to hear people continue to speak about "co-morbidity" as though the division between the two entities is a foregone conclusion (anxiety in bipolar disorder is exactly the same story, and even "OCD" sometimes merits the same kind of wondering).  

In my view, the bottom line is that we don't really know what causes these various illnesses anyway -- so dividing them is arbitrary until we know more, and if we forget that we have arbitrarily divided them, we have forgotten something important.  Of course there are some clear benefits in trying to divide these things so we can classify them better and try to understand them better. 

Here's one quote you might like though.  Paraphrasing again: when it comes to flowers and such, there are botanists and there are gardeners.  The gardeners are content to look at "all blue flowers" together as a group, regardless of genus/species/etc.  (Here's the direct quote part) "The DSM is for gardeners". 

Thanks for the opportunity for that soapbox. 

Dr. Phelps