Late complication of diphtheria:
**Core Concept**
Diphtheria is a bacterial infection caused by Corynebacterium diphtheriae, leading to the production of a toxin that can cause local and systemic complications. The toxin interferes with protein synthesis and can cause damage to various organs, including the heart, kidneys, and nervous system.
**Why the Correct Answer is Right**
The late complication of diphtheria is myocarditis, which occurs due to the toxin's effect on the heart muscle. The toxin can cause inflammation and damage to the myocardium, leading to impaired heart function, arrhythmias, and even cardiac failure. This is a result of the toxin's ability to inhibit protein synthesis, leading to the disruption of normal myocardial function.
**Why Each Wrong Option is Incorrect**
**Option A:** Myocarditis is not a rare complication of diphtheria, making it the most likely answer. Other complications, such as neurological manifestations, may occur but are not as common or well-documented as myocarditis.
**Option B:** While neurological manifestations can occur in diphtheria, they are not typically considered a late complication.
**Option C:** Renal failure can occur in diphtheria, but it is not the most well-known or common late complication.
**Clinical Pearl / High-Yield Fact**
Remember that the toxin produced by Corynebacterium diphtheriae can cause damage to various organs, and myocarditis is a well-documented late complication of the disease.
**Correct Answer:** A. Myocarditis