Primarily Obsessional OCD

Primarily cognitive obsessive-compulsive disorder (also commonly called "primarily obsessional OCD", purely obsessional OCD, Pure-O, OCD without overt compulsions or with covert compulsions) is a lesser-known form or manifestation of OCD. For people with primarily obsessional OCD, there are fewer observable compulsions, compared to those commonly seen with the typical form of OCD (checking, counting, hand-washing, etc.). While ritualizing and neutralizing behaviors do take place, they are mostly cognitive in nature, involving mental avoidance and excessive rumination. Primarily obsessional OCD often takes the form of intrusive thoughts of a distressing or violent nature.

Primarily obsessional OCD has been called "one of the most distressing and challenging forms of OCD." People with this form of OCD have "distressing and unwanted thoughts pop into [their] head frequently", and the thoughts "typically center on a fear that you may do something totally uncharacteristic of yourself, something ...potentially fatal...to yourself or others." The thoughts "quite likely, are of an aggressive or sexual nature."

The nature and type of primarily obsessional OCD varies greatly, but the central theme for all sufferers is the emergence of a disturbing intrusive thought or question, an unwanted/inappropriate mental image, or a frightening impulse that causes the person extreme anxiety because it is antithetical to closely held religious beliefs, morals, or societal mores. The fears associated with primarily obsessional OCD tend to be far more personal and terrifying for the sufferer than what the fears of someone with traditional OCD may be. Pure-O fears usually focus on self-devastating scenarios that the sufferer feels would ruin their life or the lives of those around them. An example of this difference could be that someone with traditional OCD is overly concerned or worried about security or cleanliness. While this is still distressing, it is not to the same level as someone with Pure-O, who may be terrified that they have undergone a radical change in their sexuality (i.e.: might be or might have changed into a pedophile), that they might be a murderer or that they might cause any form of harm to a loved one or an innocent person, or to themselves, or that they will go insane.

They will understand that these fears are unlikely or even impossible but the anxiety felt will make the obsession seem real and meaningful. While those without primarily obsessional OCD might instinctively respond to bizarre intrusive thoughts or impulses as insignificant and part of a normal variance in the human mind, someone with Pure-O will respond with profound alarm followed by an intense attempt to neutralize the thought or avoid having the thought again. The person begins to ask themselves constantly "Am I really capable of something like that?" or "Could that really happen?" or "Is that really me?" (even though they usually realize that their fear is irrational, which causes them further distress) and puts tremendous effort into escaping or resolving the unwanted thought. They then end up in a vicious cycle of mentally searching for reassurance and trying to get a definitive answer.

...
Wikipedia