A 50-year-old woman with long-standing rheumatoid ahritis complains of weakness and fatigue. She states that her stools have recently become black after taking a new nonsteroidal anti-inflammatory drug (NSAID). Gastroscopy shows numerous superficial, bleeding mucosal defects. Which of the following is the most likely diagnosis?

**Core Concept**
The patient's presentation with weakness, fatigue, black stools, and bleeding mucosal defects on gastroscopy suggests a condition related to gastrointestinal mucosal damage, likely due to nonsteroidal anti-inflammatory drug (NSAID) use.

**Why the Correct Answer is Right**
The patient's symptoms are consistent with a diagnosis of NSAID-induced gastritis, which is characterized by mucosal damage and bleeding. This condition is a common side effect of NSAID use, particularly in patients with underlying conditions such as rheumatoid arthritis. The use of NSAIDs inhibits the production of prostaglandins, which are essential for maintaining the protective mucosal lining of the stomach.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not relevant to the patient's presentation, as it refers to a condition related to the small intestine.
* **Option B:** This option is incorrect, as it refers to a condition related to the pancreas, which is not relevant to the patient's symptoms.

**Clinical Pearl / High-Yield Fact**
NSAIDs can cause gastrointestinal mucosal damage and bleeding by inhibiting prostaglandin production, which is essential for maintaining the protective mucosal lining of the stomach. This is a common side effect of NSAID use, particularly in patients with underlying conditions such as rheumatoid arthritis.

**Correct Answer:** C.

✓ Correct Answer: A. Acute erosive gastritis