What is the differential diagnosis for a 60-year-old man with severe diffuse abdominal pain, hypertension, tachycardia, hyperglycemia, and an anion gap of 18, with a past medical history of Coronary Artery Disease (CAD) status post Percutaneous Coronary Intervention (PCI), Heart Failure (HF) with reduced Ejection Fraction (HFrEF), Type 2 Diabetes Mellitus (T2DM), Gastroesophageal Reflux Disease (GERD), and Hepatitis C (Hep C)?

Differential Diagnosis for Severe Diffuse Abdominal Pain with Elevated Anion Gap

The most critical diagnosis to rule out immediately in this patient is acute mesenteric ischemia, given the combination of severe diffuse abdominal pain, elevated anion gap metabolic acidosis (AG 18), cardiovascular disease, diabetes, and hemodynamic instability. 1

Life-Threatening Diagnoses Requiring Immediate Evaluation

Acute Mesenteric Ischemia (AMI)

• This is the most urgent diagnosis to exclude given the constellation of severe diffuse abdominal pain, elevated anion gap (18), diabetes, and cardiovascular disease 1, 2
• The elevated anion gap indicates lactic acidosis from tissue hypoperfusion, which is characteristic of bowel ischemia 1
• Diabetic patients with cardiovascular disease have significantly increased risk for both occlusive and non-occlusive mesenteric ischemia (NOMI) 3, 2
• Key clinical features to assess:
  • Pain out of proportion to physical examination findings 1
  • Persistent or worsening acidosis despite fluid resuscitation 1
  • Tachycardia and hypertension may represent compensatory response to severe pain and tissue ischemia 1
• Immediate diagnostic step: CT angiography of the abdomen to evaluate mesenteric vessels and bowel wall integrity 1, 2

Diabetic Ketoacidosis (DKA) with Complications

• The anion gap of 18 with hyperglycemia strongly suggests DKA as either primary diagnosis or complicating factor 3, 1, 2
• Critical association: DKA itself can precipitate mesenteric ischemia through volume depletion, hyperviscosity, and hypercoagulability 1, 2
• DKA with concurrent mesenteric ischemia has been reported in adult diabetic patients and carries extremely high mortality 1
• Assess for: Serum ketones, beta-hydroxybutyrate, arterial blood gas showing metabolic acidosis with elevated anion gap 4

Acute Coronary Syndrome (ACS)

• Given history of CAD status post PCI, acute MI must be considered as abdominal pain can be an atypical presentation 4
• Tachycardia, hypertension, and metabolic derangements may indicate cardiac ischemia 4
• Immediate evaluation: 12-lead ECG, high-sensitivity cardiac troponins at presentation and serially 4
• Diabetic patients have worse outcomes with ACS and may present atypically 4, 5

Acute Decompensated Heart Failure

• Patient has known HFrEF, which increases risk for cardiogenic shock and end-organ hypoperfusion 6
• Elevated anion gap may reflect lactic acidosis from poor cardiac output and tissue hypoperfusion 7
• Assess for: Signs of volume overload, hypotension, elevated jugular venous pressure, pulmonary edema 6

Other Important Differential Diagnoses

Gastrointestinal Causes

• Perforated viscus (peptic ulcer given GERD history): Look for peritoneal signs, free air on imaging 4
• Acute pancreatitis: Check lipase, amylase; assess for epigastric tenderness radiating to back 4
• Cholecystitis/cholangitis: Right upper quadrant tenderness, fever, elevated bilirubin 4
• Bowel obstruction: Assess for distension, absent bowel sounds, dilated bowel loops on imaging 4

Vascular Catastrophes

• Aortic dissection: Assess for tearing chest/back pain, pulse deficits, widened mediastinum on chest X-ray 4
• Ruptured abdominal aortic aneurysm: Pulsatile abdominal mass, hypotension, flank ecchymosis 4

Metabolic/Endocrine

• Lactic acidosis from metformin (if patient taking metformin): Check lactate level, assess renal function 4
• Uremic acidosis: Evaluate for acute kidney injury given diabetes and heart failure 4

Diagnostic Algorithm Priority

Step 1 (Immediate - within minutes):

• 12-lead ECG to rule out STEMI 4
• Point-of-care glucose, venous blood gas with lactate 4, 1
• High-sensitivity cardiac troponins 4
• Complete metabolic panel including renal function 4

Step 2 (Urgent - within 1 hour):

• CT angiography of abdomen/pelvis with IV contrast if renal function permits - this is the single most important test to diagnose mesenteric ischemia 1, 2
• Serum ketones/beta-hydroxybutyrate if DKA suspected 4
• Lactate level (elevated lactate with high anion gap strongly suggests tissue ischemia) 1, 7
• Lipase for pancreatitis 4

Step 3 (Based on initial results):

• If CT shows mesenteric ischemia: Immediate surgical consultation - mortality approaches 60-80% without urgent intervention 1
• If cardiac biomarkers positive: Cardiology consultation, consider urgent cardiac catheterization 4
• If DKA confirmed: Aggressive fluid resuscitation, insulin therapy, but maintain high suspicion for concurrent mesenteric ischemia if acidosis does not improve 1, 2

Critical Clinical Pitfalls

• Do not attribute elevated anion gap solely to DKA without excluding mesenteric ischemia - these conditions frequently coexist and mesenteric ischemia is rapidly fatal 1, 2
• Worsening or persistent acidosis despite appropriate DKA treatment mandates immediate imaging for bowel ischemia 1
• Diabetic patients with cardiovascular disease have multiple risk factors for mesenteric ischemia including atherosclerosis, low cardiac output from HFrEF, and hypercoagulability 3, 1, 2
• The combination of severe pain with relatively benign abdominal examination ("pain out of proportion") is classic for early mesenteric ischemia before peritonitis develops 1
• Elevated anion gap in CAD patients independently predicts mortality and disease severity - this finding should heighten concern for serious pathology 7