Pseudomembranes

Pseudomembranes are adherent, layered accumulations on mucosal surfaces composed chiefly of fibrin, necrotic epithelial cells, inflammatory cells, and mucus, often overlying inflamed tissue. They are called pseudomembranes because, unlike true membranes, they are not a distinct tissue layer but a structured exudate that adheres to the underlying mucosa.

Pseudomembranes form in conditions that cause extensive mucosal injury and inflammatory exudation. They may be seen in the pharynx and larynx, in the colon, or on conjunctival surfaces. Clinically they present as a grayish-white to yellowish membrane that can be peeled away, sometimes with bleeding, with surrounding erythema.

Most well-known examples are infectious: the pharyngeal pseudomembrane of diphtheria, caused by Corynebacterium diphtheriae toxin, and pseudomembranous colitis due to Clostridioides difficile infection following antibiotic use. Other contexts include pseudomembranous conjunctivitis and, less commonly, mucosal lesions from severe inflammatory diseases.

Management focuses on treating the underlying cause and, when appropriate, removing the membrane cautiously to relieve obstruction or bleeding. Diphtheria requires antitoxin and antibiotics; pseudomembranous colitis is treated with targeted antibiotics such as oral vancomycin or fidaxomicin. Diagnosis is clinical supported by culture, toxin testing, or PCR, as indicated.