A 6-year-old child develops fever, sore throat, and a grayish-white membrane over the tonsils that bleeds on attempted removal. Neck swelling is prominent ('bull neck'). Blood pressure falls over the next few hours. The mechanism responsible for the cardiovascular complications in this disease is:

• A Direct bacterial invasion of the myocardium
• B Type III hypersensitivity immune complex deposition
• C Superantigen-mediated cytokine storm
• D Exotoxin-mediated inhibition of protein synthesis in cardiac cells ✓

Explanation

Diphtheria toxin (produced by Corynebacterium diphtheriae lysogenised by beta-phage) inhibits protein synthesis by ADP-ribosylating elongation factor EF-2. This affects all protein-synthesizing cells; cardiac myocytes are particularly susceptible, causing toxic myocarditis with arrhythmias, heart block, and circulatory collapse. The toxin acts locally and systemically — it does not require direct bacterial invasion. Type III hypersensitivity and superantigen mechanisms are seen in streptococcal/staphylococcal diseases.

Reference: Ghai Essential Pediatrics, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.