pseudomembranous

Pseudomembranous is an adjective used in medicine to describe the formation of a pseudomembrane on a mucosal surface. A pseudomembrane is an adherent layer composed of fibrin, inflammatory cells, necrotic epithelial cells, mucus, and bacteria that sits atop the underlying tissue during certain inflammatory or infectious processes. It most often involves mucous membranes of the gastrointestinal tract or upper airways, but can occur in other sites such as the conjunctiva. The term reflects a false membrane rather than a true, intact tissue layer.

Two widely known contexts are pseudomembranous colitis and diphtheria. Pseudomembranous colitis is most commonly caused by overgrowth of Clostridioides difficile after antibiotic exposure and presents with watery diarrhea, abdominal pain, fever, and leukocytosis; the colon may develop raised, yellowish plaques. Diphtheria produces a thick pseudomembrane on the oropharyngeal or nasopharyngeal mucosa that can cause odynophagia, fever, and potential airway obstruction if extensive.

Diagnosis relies on clinical presentation combined with targeted testing. For suspected pseudomembranous colitis, stool assays for C. difficile toxins and toxins genes, along with clinical correlation, are used; endoscopy may reveal pseudomembranes on affected segments. Diphtheria is diagnosed by throat culture or molecular testing for Corynebacterium diphtheriae, supported by the appearance of the pharyngeal membrane.

Treatment is directed at the underlying cause. Pseudomembranous colitis is managed with stopping the inciting antibiotic and providing targeted anti-C. difficile therapy (for example, oral vancomycin or fidaxomicin) and supportive care. Diphtheria requires antitoxin and appropriate antibiotics, with vaccination to prevent recurrence. The prognosis varies with disease severity and promptness of treatment. Etymology-wise, the term derives from pseudo- meaning false and membrane.