Purple lining over gums is seen in which chronic poisoning:
**Core Concept**
Chronic poisoning with certain heavy metals can lead to distinctive mucocutaneous manifestations, including changes in the oral mucosa. One such sign is the appearance of purple or blue-black discoloration of the gums.
**Why the Correct Answer is Right**
The correct answer is related to the deposition of a specific heavy metal in the gums, which causes the characteristic discoloration. The metal in question is **lead (Pb)**, which is known to accumulate in the gums, causing a purple or blue-black line to form along the gingival margins. This is due to the deposition of lead sulfide, which is a dark-colored compound that can be seen as a line along the gums. The mechanism involves the binding of lead to sulfhydryl groups in the gingival tissue, leading to the formation of lead sulfide.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not relevant to the chronic poisoning causing purple lining over gums.
* **Option B:** This option is incorrect because it does not relate to the specific heavy metal causing the discoloration.
* **Option C:** This option is incorrect because it is not associated with the characteristic purple lining over gums.
**Clinical Pearl / High-Yield Fact**
In addition to the characteristic purple lining, chronic lead poisoning can also cause a range of other symptoms, including abdominal pain, constipation, and neuropathy. It is also worth noting that lead poisoning can be caused by exposure to lead-based paints, contaminated water, or certain industrial processes.
**Correct Answer:** C. Lead poisoning.