Differential Diagnosis: Acute-on-Chronic Epigastric Pain with Shoulder Referral

1. Biliary Tract Disease (Top Priority)

• Harrison's (2025) describes biliary colic as a "steady ache or fullness in the epigastrium or right upper quadrant (RUQ) with frequent radiation to the interscapular area, right scapula, or shoulder" — a near-perfect match for this presentation.
• Pain is steady (not truly colicky), lasts 30 min to 5 h, often nocturnal, precipitated by fatty meals.
• Referred shoulder pain in biliary disease is via the phrenic nerve (C3–C5) — diaphragmatic irritation from an inflamed/distended gallbladder refers to the right shoulder tip.
• Normal bloods do not exclude gallstones — LFTs and bilirubin are often normal in uncomplicated biliary colic.

2. PPI-Related Effects — Yes, This Is Clinically Relevant

a) Rebound Acid Hypersecretion on PPI Withdrawal/Stopping

"Abrupt withdrawal of a PPI in a long-term user may result in a component of rebound hyperacidity; thus, this agent should be tapered gradually over the course of 1–2 weeks with possible transition to an H2 blocker." — Harrison's Principles, 22nd Ed.

• When PPIs are stopped abruptly after long-term use, rebound acid hypersecretion can occur for days to weeks. This causes worse dyspepsia, epigastric burning, and reflux symptoms than the original condition.
• The patient reports improvement after stopping the PPI — this is actually the opposite of rebound. This suggests the PPI itself may have been contributing to the symptoms (see below).

b) PPI-Induced Hypochlorhydria and Altered Digestion

• Small intestinal bacterial overgrowth (SIBO) — profound acid suppression permits bacterial overgrowth, leading to bloating, epigastric discomfort, nausea.
• Altered gut motility — PPIs interact with gastrin physiology.
• Collagenous colitis — lansoprazole specifically has a hazard ratio of 4.5 for collagenous colitis; this causes diarrhea and abdominal pain that resolves when the PPI is stopped. The patient is on lansoprazole — clinically significant.
• Hypomagnesaemia — long-term PPI use causes a 40% increased risk of hypomagnesaemia (even with normal routine bloods if Mg wasn't specifically checked), which can cause muscle cramping and epigastric discomfort.

c) PPI Interaction with Clopidogrel (If Applicable)

3. Peptic Ulcer Disease (PUD) / H. pylori

• Long-term acid reflux with chronic PPI use can mask peptic ulcers. PPI suppression provides symptomatic relief but if H. pylori is present, underlying mucosal damage continues.
• H. pylori is a cause of both ulcer and non-ulcer dyspepsia. Importantly, H. pylori breath test or stool antigen should be done OFF PPIs for at least 2 weeks — if tested while on lansoprazole, a false negative is likely.
• The pain improvement on stopping PPI could reflect reduced gastric mucosal coverage, exposing a true ulcer — or alternatively, removing a drug causing side effects.
• Zollinger-Ellison syndrome (gastrinoma) is rare but should be considered in refractory or recurrent ulcer disease — causes massive acid hypersecretion.

4. Chronic Pancreatitis / Pancreatic Pathology

• Epigastric pain radiating to the back and sometimes shoulder is classic.
• In chronic pancreatitis, pain is dull, gnawing, may fluctuate with food intake.
• Risk factors include prior biliary disease, alcohol use.
• Normal routine bloods do not exclude chronic pancreatitis (amylase/lipase may be normal in chronic disease).

5. Diaphragmatic Irritation — Free Air / Subphrenic Collection

• Post-perforated ulcer or subphrenic abscess → bilateral shoulder tip pain via diaphragmatic irritation.
• Excluded only if imaging has been done.

6. Aortic Aneurysm / Aortic Pathology

• D-dimer is normal and this would more typically present acutely with back/tearing pain, but in a 62-year-old male with MI history and chronic epigastric symptoms, abdominal aortic aneurysm (AAA) deserves at least a clinical screen (abdominal palpation, ultrasound).

7. Referred Cardiac / Musculoskeletal

• Troponin and ECG are normal — acute MI excluded. However, stable angina equivalent presenting as epigastric pain is possible in elderly diabetic or post-MI patients with atypical presentations. An exercise stress test or further cardiac imaging may still be warranted.
• Musculoskeletal (lower costal chondritis, hiatal hernia) can mimic this pain pattern.

Why Symptoms Improved on Stopping Lansoprazole

Recommended Next Steps

1. Abdominal ultrasound — biliary tree, pancreas, aorta
2. H. pylori testing (off PPI for ≥2 weeks) — urea breath test or stool antigen
3. Serum magnesium, B12, FBC — PPI-related deficiencies
4. Upper GI endoscopy — assess for peptic ulceration, oesophagitis, gastric pathology
5. Serum amylase/lipase + CT abdomen if pancreatitis suspected
6. Fasting serum gastrin if recurrent ulcers or ZE syndrome suspected
7. Cardiac stress test — given MI history and atypical presentations