Pseudomembranous Colitis

What "pseudomembranous" means

A true membrane is a sheet of living tissue. A pseudomembrane ("false membrane") is a layer of debris stuck to the colon wall: fibrin, mucus, dead lining cells and white blood cells. In C. diff infection, toxins A and B damage the cells of the colon lining, triggering intense inflammation. Small volcano-like eruptions of inflammatory material spread over the surface and merge into raised yellow or white plaques 2 to 10 mm across.

The term describes what the colon looks like on colonoscopy or under the microscope. Not everyone with C. diff develops pseudomembranes; they mark a more severe stage. For the broader infection, including spread and prevention, see C. diff colitis.

Causes

• C. difficile toxins: responsible for the vast majority of cases. The main trigger is disruption of the normal gut bacteria by antibiotics, especially clindamycin, fluoroquinolones, cephalosporins and broad-spectrum penicillins, although almost any antibiotic can do it.
• Other risk factors: age over 65, hospital or nursing home stays, acid-suppressing medicines (PPIs), chemotherapy, weakened immunity, inflammatory bowel disease, and previous C. diff.
• Rare non-C. diff causes: ischemic colitis, some other infections (such as Staphylococcus aureus, Klebsiella oxytoca, shigella or cytomegalovirus), certain chemotherapy drugs and heavy metal poisoning can produce similar appearances.

Symptoms

• watery diarrhea, often 3 to 15 or more times a day, with a distinctive smell
• crampy lower abdominal pain and tenderness
• fever
• nausea, loss of appetite
• mucus in the stool; visible blood is uncommon but possible
• dehydration, weakness and weight loss

Symptoms usually begin within the first few days to 2 weeks of starting antibiotics, but can begin up to 2 to 3 months after finishing them.

How it is diagnosed

1. Stool tests: a PCR test for the C. diff toxin gene, often combined with a toxin test to confirm active disease. Only unformed (liquid) stool is tested.
2. Blood tests: white cell count, creatinine and lactate to grade severity; albumin is often low.
3. CT scan: shows a thickened colon wall, the "accordion sign" of swollen folds, fluid around the colon, and complications such as megacolon or perforation.
4. Colonoscopy or flexible sigmoidoscopy: not routinely needed, but shows pseudomembranes directly. It is used when the diagnosis is unclear, stool tests are negative, or other conditions such as ulcerative colitis need excluding. It is avoided in severe disease because of perforation risk.

How severe is it?

The IDSA/SHEA guideline grades C. diff infection to guide treatment:

Treatment

First steps

• Stop the triggering antibiotic if possible, or switch to a lower-risk choice.
• Fluids and electrolytes by mouth or IV.
• Avoid anti-diarrheal medicines such as loperamide in the acute phase unless a doctor advises them, because slowing the gut can worsen toxin effects.
• Review and stop unnecessary PPIs.

Antibiotic treatment for C. diff

• Fidaxomicin for 10 days: preferred in guidelines because it lowers recurrence.
• Oral vancomycin for 10 days: an effective alternative.
• Metronidazole by mouth is now used only for non-severe cases when the others are unavailable.

Fulminant disease

• High-dose oral vancomycin, plus vancomycin given rectally if the gut is not moving, plus IV metronidazole.
• Surgical review early. Colectomy (removal of the colon) or a loop ileostomy with colon lavage can be lifesaving when there is perforation, toxic megacolon or worsening despite treatment.

Preventing recurrence

About 1 in 6 people have a recurrence. Options include a fidaxomicin course, a tapered and pulsed vancomycin course, bezlotoxumab (an antibody infusion, availability varies) and, for multiple recurrences, fecal microbiota-based therapies, including FDA-approved products and fecal microbiota transplantation.

Complications

• dehydration and acute kidney injury
• toxic megacolon: dangerous dilation of the colon
• bowel perforation and peritonitis
• sepsis
• low protein levels and swelling
• recurrent infection

Outlook

Most people with pseudomembranous colitis recover fully with prompt treatment, typically improving within 3 to 5 days. The risk of death rises with age, frailty, and fulminant disease. Recurrence is common in the first 8 weeks, so new diarrhea after treatment should be reported promptly.

Frequently asked questions

What is the main cause of pseudomembranous colitis?

Almost all cases are caused by toxins from Clostridioides difficile. The usual trigger is antibiotic treatment, which kills the normal gut bacteria that keep C. diff under control. Hospital stays, older age and acid-suppressing medicines further raise the risk.

Is pseudomembranous colitis the same as C. diff?

Not exactly. C. diff infection ranges from mild diarrhea to life-threatening colitis. Pseudomembranous colitis describes the more severe form where plaques form on the colon lining. Nearly all pseudomembranous colitis is due to C. diff, but not all C. diff infections show pseudomembranes.

How is pseudomembranous colitis treated?

It is treated with oral fidaxomicin or vancomycin for about 10 days, plus stopping the triggering antibiotic and replacing fluids. Severe or fulminant disease needs hospital care, higher-dose combined treatment and sometimes surgery to remove the colon.

Can pseudomembranous colitis be seen on a CT scan?

A CT scan cannot show the plaques themselves, but it shows the effects: a thickened colon wall, swollen folds (the accordion sign) and fluid around the colon. It also detects complications such as megacolon or perforation. Colonoscopy shows the pseudomembranes directly.

How long does it take to recover?

Most people notice improvement within 3 to 5 days of starting treatment and finish a 10-day course. Bowel habits can take several weeks to return to normal. Around 1 in 6 people get a recurrence, usually within 8 weeks.