Yellow discoloration of skin and mucosa is seen in which poisoning?
**Core Concept**
The question is testing the student's knowledge of the characteristic cutaneous manifestations of various poisonings. This involves understanding the pathophysiological mechanisms underlying the discoloration of skin and mucosa due to chemical exposure.
**Why the Correct Answer is Right**
The correct answer is related to the Arsenic poisoning, which is known to cause a characteristic yellow discoloration of the skin and mucosa. This is due to the deposition of arsenic in the skin, leading to a condition known as "arsenic pigmentation" or "raindrop pigmentation". The mechanism involves the binding of arsenic to the sulfhydryl groups of proteins, leading to the formation of arsenic-protein complexes, which are then deposited in the skin, causing the characteristic yellow discoloration.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because Mercury poisoning typically causes a blue-black discoloration of the skin, known as "blue line" or "Hutchinson's sign", due to the deposition of mercury sulfide in the skin.
* **Option B:** This option is incorrect because Lead poisoning causes a range of cutaneous manifestations, including pallor, petechiae, and ecchymoses, but not yellow discoloration of the skin.
* **Option C:** This option is incorrect because Carbon monoxide poisoning causes a cherry-red discoloration of the skin and mucosa due to the formation of carboxyhemoglobin.
**Clinical Pearl / High-Yield Fact**
It is essential to remember that the characteristic cutaneous manifestations of poisonings can provide valuable clues to the diagnosis of poisoning. A thorough history and physical examination, combined with laboratory tests, can help identify the underlying cause of the discoloration.
**Correct Answer: A. Arsenic poisoning.**