Commonest complication of diptheria:
**Core Concept**
Diphtheria is a bacterial infection caused by Corynebacterium diphtheriae, characterized by the formation of a thick, gray membrane in the throat. The toxin produced by the bacteria, diphtheria toxin, is responsible for the majority of the disease's complications.
**Why the Correct Answer is Right**
The correct answer is myocarditis, which is the inflammation of the heart muscle. This occurs due to the systemic effects of the diphtheria toxin, which can cause damage to various tissues, including the heart. The toxin works by inhibiting protein synthesis in cells, leading to cell death and tissue damage. Myocarditis can lead to heart failure, arrhythmias, and even death if left untreated.
**Why Each Wrong Option is Incorrect**
* **Option A:** Paralysis is a possible complication of diphtheria, but it is not the most common one. Paralysis occurs due to the toxin's effect on the nervous system, but it is less frequent than myocarditis.
* **Option B:** Laryngitis is a possible complication of diphtheria, but it is not the most common one. Laryngitis occurs due to the formation of a membrane in the larynx, but it is less frequent than myocarditis.
* **Option C:** Bronchopneumonia is a possible complication of diphtheria, but it is not the most common one. Bronchopneumonia occurs due to the bacterial infection itself, but it is less frequent than myocarditis.
**Clinical Pearl / High-Yield Fact**
Diphtheria toxin's mechanism of action involves the inhibition of protein synthesis by inactivating the enzyme elongation factor-2 (EF-2), leading to cell death and tissue damage. This is a key point to remember for exam purposes.
**Correct Answer: C. Myocarditis**