Though my primary flavor of OCD is contamination/washer I have occasional bouts of Pure O (obsession without external obvious compulsions), which sucks. And while I don’t think one form of OCD is any worse then another, having Pure O on top of contamination stuff is rather hellish. I suspect that since Pure O is much easier to hide from others that folks that have this as their primary manifestation tend to not get help for even longer times then is usual and probably as a result tend to feel even more isolated. Not to mention that the content of the Pure O obsessions can be very disturbing and folks with it can be very reluctant to share it with others for fear of repercussions.
This is an excellent article on Pure O by a person with that form of OCD