This is also routinely misdiagnosed until the patient is in really bad shape. Happened to a friend of mine. He was having constipation, cramps, the whole nine yards. He went to his doctor, who prescribed some kind of laxative, which, of course, didn't help much.
He made another trip or two, and then finally ended up in the ER. They thought he had appendicitis, and scheduled him for surgery.
Finally, a doctor saw him who apparently had some sense and sent him for an ultrasound and a CT scan, which of course, showed the distension. He was treated for the distended colon and made a full recovery, but I shudder to think what would have happened if he had been opened up and the surgeon couldn't find a hot appendix, but found a very bloated colon.