**Core Concept:**
The patient presents with epigastric pain that is radiating to the back, relieved by food intake, and worsened by fasting. This clinical scenario is consistent with a post-operative complication following a perforated duodenal ulcer repair with omental patch technique. Proton pump inhibitors (PPIs) and analgesics have been effective in controlling the pain before and after surgery.

**Why the Correct Answer is Right:**
The correct answer is **D** - PPI-responsive epigastric pain with radiation to the back. The patient's history of perforated duodenal ulcers, surgical history with omental patch repair, and the relief of pain by PPIs and analgesics all point towards a post-operative complication. PPI-responsive pain radiating to the back is a characteristic presentation of a spinal cord irritation due to a herniation of the omentum through the previous surgical site, which is known as "enteric hernia" or "enteric fistula".

**Why Each Wrong Option is Incorrect:**
A. Gastroesophageal reflux disease (GERD) is a misdiagnosis because the pain is relieved by PPIs, while GERD pain worsens on PPIs.
B. Peptic ulcer pain is incorrect because the pain is relieved by PPIs, while peptic ulcer pain is worsened by PPIs.
C. Acid peptic ulcer pain is incorrect for the same reason as peptic ulcer pain.

**Clinical Pearl:**
In patients with post-operative pain presentation like this, a thorough history focusing on the surgical history is crucial. Post-surgical complications should be considered in the differential diagnosis, especially in patients with a history of peptic ulcer disease. This case highlights the importance of PPIs in managing pain in these patients, as it demonstrates the role of PPIs in reducing acid production and alleviating pain due to post-operative complications like herniation of the omentum through the surgical site.