Diphtheria is caused by toxin-producing strains of Corynebacterium diphtheriae. The bacteria colonize the upper respiratory tract or skin. In respiratory disease, local tissue necrosis and inflammatory exudate produce a thick adherent pseudomembrane. Attempting to remove the membrane can cause bleeding and worsen airway obstruction. The toxin can enter the bloodstream and damage distant tissues, especially the myocardium and peripheral nerves. This is why diphtheria is not just a throat infection; it is a systemic toxin-mediated disease. For NCLEX-RN (Canada), items rarely announce the topic in the first sentence. Anchor to objective data, trajectory, and the safest next step for the role named in the stem before distractors compete. On the exam, writers often pair stable-sounding options with unstable data—notice the mismatch before you commit. If the stem names a license or role, reread that line; scope errors are classic trap answers even when the clinical topic is familiar. Run a 60-second scan: breathing work and oxygenation, perfusion and end organs, neuro baseline, likely infection sources, and devices that can fail quietly. When two answers feel partly right, pick the one...