Is colitis difficult to diagnose? i had a colonscopy done by one doctor. he said i have colitis. i went to another doctor for a second opinion. he looked at pathology report and declared there is no colitis. who can i believe?

Different interpretation from different information. One doc actually looked up your colon and saw irritation- which is a basic definition of colitis. The other looked at a pathology report, I assume describing a sample taken during the test & decided the sample did not support HIS definition of colitis. I can see where both were right. The 2nd just doesn't think it is bad enough to label colitis

Yes, relatively common, the initial diagnosis was formulated on symptoms and exam suggesting inflammation ( visual changes), while the actual microscopic exam might have not supported the clinical diagnosis. The decider would be your symptoms at the time, if consistent with colitis or not, the actual cause or etiology might remain unclear due to non diagnostic findings on pathology.