## **Core Concept**
The question pertains to the identification of a pathognomonic lesion known as a "tophus" and its association with a specific medical condition. A tophus is a deposit of crystalline uric acid and other substances at the surface of joints or in the skin, often seen in chronic gout.

## **Why the Correct Answer is Right**
The correct answer, **C. Gout**, is associated with tophi formation. Tophi are pathognomonic for gout, a form of inflammatory arthritis characterized by sudden, severe attacks of pain, swelling, redness, and tenderness in one or more joints, most often in the big toe. These deposits form due to the accumulation of monosodium urate crystals and are a hallmark of chronic gout.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because it does not correspond with the formation of tophi.
- **Option B:** Similarly, this option does not relate to the condition characterized by tophi formation.
- **Option D:** This option is also incorrect as it does not represent the condition associated with tophi.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that the presence of tophi is a diagnostic criterion for gout and signifies chronic disease. Tophi can be found in various locations, including the ears, fingers, toes, and bursae, and their presence helps differentiate gout from other forms of arthritis.

## **Correct Answer: C. Gout**