Pseudomembranous Colitis - Diagnosis

Diagnosis

In order to make the diagnosis, it is, of course, essential that the treating physician be aware of any recent antibiotic usage. The disease may occur as late as six months after antibiotic use. Although there is some relationship between dose/duration of antibiotic and the likelihood of developing pseudomembranous colitis, it may occur even after a single dose of antibiotic. In fact, the use of a single-dose prophylactic antibiotic is a common practice in surgical and dental patients to prevent infections associated with a procedure. Hence, even though unlikely to cause pseudomembranous colitis on a per-case basis, single-dose antibiotic treatment, by virtue of the large number of patients receiving such, is an important cause of pseudomembranous colitis. Use of 'proton pump inhibitor' drugs such as omeprazole for gastric reflux, or some forms of asthma inhaler, in fact, all drugs with anticholinergic effects that slow the digestive transit time lead to retention of toxins and exacerbate the effects of broad-spectrum antibiotics.

Prior to the advent of tests to detect Clostridium difficile toxins, the diagnosis was most often made by colonoscopy or sigmoidoscopy. The appearance of "pseudomembranes" on the mucosa of the colon or rectum is diagnostic of the condition. The pseudomembranes are composed of an exudate made of inflammatory debris, white blood cells, etc.

Although colonoscopy and sigmoidoscopy are still employed, stool testing for the presence of Clostridium difficile toxins is now often the first-line diagnostic approach. Usually, only two toxins are tested for - Toxin A and Toxin B - but the organism produces several others. This test is not 100% accurate, and there is a considerable false negative rate even with repeat testing.

Another, more recent two-step approach involves testing for the presence of C. Diff in the stool and then testing for toxin production. The first step is performed by testing for the presence of the C. Diff GDH antigen. If the first step is positive, a second test, a PCR assay targeting the toxin genes, is performed.