**Question:** A patient with suspected poisoning has brownish oral mucosa and tongue, constricted pupil and greenish brown urine, poisoning is with

A. Lead
B. Mercury
C. Urometry
D. Thallium

**Core Concept:**
Poisoning can present with a variety of clinical signs and symptoms depending on the toxic substance involved. The given symptoms suggest the involvement of a heavy-metal poisoning. Heavy-metal poisoning often leads to toxic effects on the nervous system, gastrointestinal tract, and renal system.

**Why the Correct Answer is Right:**
The correct answer is D. Thallium poisoning, as the clinical symptoms and signs described in the question are consistent with the toxic effects of thallium poisoning. Thallium is a heavy-metal, and when ingested, it causes toxic effects due to its high affinity for sulfhydryl groups of proteins, inhibiting enzymes and causing cellular damage.

**Why Each Wrong Option is Incorrect:**
A. Lead poisoning: Lead poisoning can present with similar symptoms, but the urine color is usually dark brown, not greenish brown.
B. Mercury poisoning: While mercury poisoning can cause oral discoloration, it is less likely to cause constricted pupils and greenish brown urine.
C. Urometry is a test used to assess kidney function, not a poisoning cause.

**Why Each Wrong Option is Incorrect:**
A. Lead poisoning: Lead poisoning can present with similar symptoms, but the urine color is usually dark brown, not greenish brown.
B. Mercury poisoning: While mercury poisoning can cause oral discoloration, it is less likely to cause constricted pupils and greenish brown urine.
C. Urometry is a test used to assess kidney function, not a poisoning cause.

**Clinical Pearl:**
Thallium poisoning is a rare but serious medical emergency, and early recognition and management are crucial. Prompt treatment involves decontamination, supportive care, and specific antidotes for thallium poisoning, like dimercaprol (British Anti-Lewisite) and thiocarbamide.