**Question:** All are complications of diphtheria, except-

A. Cerebrospinal meningitis
B. Polyneuropathy
C. Congestive heart failure
D. Acute respiratory distress syndrome

**Core Concept:** Diphtheria is a severe bacterial infection caused by the bacterium Corynebacterium diphtheriae. It primarily affects the respiratory tract but can also cause systemic complications due to toxin production. Diphtheric toxin interferes with the normal function of neuromuscular junctions and cardiovascular system, leading to various complications.

**Why the Correct Answer is Right:** The correct answer (D) refers to Acute Respiratory Distress Syndrome (ARDS), which is a severe lung inflammation leading to decreased oxygen exchange in the lungs. ARDS is a separate entity with distinct pathophysiology and is not a complication of diphtheria.

**Why Each Wrong Option is Incorrect:**

A. Cerebrospinal meningitis: Cerebrospinal meningitis is an infection of the meninges (lining of the brain and spinal cord) caused by various pathogens, not specifically related to diphtheria.

B. Polyneuropathy: Polyneuropathy is a complication of diphtheria involving damage to peripheral nerves, characterized by muscle weakness and sensory loss.

C. Congestive heart failure: Congestive heart failure is a complication related to myocardial damage caused by diphtheria toxin, affecting the heart's ability to pump blood effectively.

**Clinical Pearl:**

Understanding the various complications of diphtheria is essential for proper diagnosis and management. Diphtheria complications primarily involve the respiratory tract, cardiovascular system, and nervous system. Prompt diagnosis and treatment with antitoxin therapy can prevent severe complications and reduce morbidity and mortality.