What is the likely diagnosis and appropriate work‑up and management for a 31‑year‑old man who developed post‑prandial dizziness and derealisation 30–60 minutes after meals for the past two weeks, without any prior gastric surgery?

Dumping Syndrome Without Prior Surgery: Diagnosis and Management

This patient most likely has late dumping syndrome (postprandial hypoglycemia), which can occur without gastric surgery, though this is extremely rare and requires excluding all other causes of reactive hypoglycemia before making this diagnosis. 1, 2

Critical Diagnostic Consideration

The fundamental issue here is that dumping syndrome is defined by its occurrence after surgeries that alter gastric anatomy—including Roux-en-Y gastric bypass, sleeve gastrectomy, esophagectomy, vagotomy with pyloroplasty, and cholecystectomy. 1, 2, 3 The absence of surgical history makes this diagnosis highly unlikely and mandates a comprehensive workup for alternative causes of postprandial hypoglycemia.

Symptom Pattern Analysis

The timing and symptoms are consistent with late dumping syndrome:

• Symptoms occur 30-60 minutes postprandially (late dumping typically occurs 1-3 hours after meals, but can begin as early as 60 minutes) 4, 1
• Dizziness and derealisation represent neuroglycopenic symptoms from reactive hypoglycemia 1, 2
• Late dumping results from incretin-driven hyperinsulinemic response causing reactive hypoglycemia 1-3 hours postprandially 1

Essential Differential Diagnoses to Exclude First

Before considering dumping syndrome without surgery, you must rule out:

1. Insulinoma (most critical alternative):

• Causes fasting hypoglycemia rather than postprandial hypoglycemia, which is the key distinguishing feature 1, 2
• Obtain fasting glucose, insulin, C-peptide, and proinsulin during a supervised 72-hour fast 1

2. Surreptitious insulin or sulfonylurea use:

• Measure C-peptide and sulfonylurea assays during symptomatic episodes 1, 2
• Low C-peptide with hypoglycemia suggests exogenous insulin administration 1

3. Other endocrine causes:

• Thyroid function tests to exclude hyperthyroidism 3
• Cortisol and ACTH if adrenal insufficiency suspected 3

4. Occult prior surgery:

• Specifically ask about any upper GI surgery, including cholecystectomy, fundoplication, or bariatric procedures 2, 3
• Even cholecystectomy can cause bile acid malabsorption with similar postprandial symptoms 3

Diagnostic Workup Algorithm

Step 1: Confirm hypoglycemia during symptoms

• Continuous glucose monitoring to capture spontaneous hypoglycemic episodes 2
• Document plasma glucose <2.8 mmol/L (50 mg/dL) or <3.3 mmol/L (60 mg/dL) when symptoms occur 2
• Obtain simultaneous insulin, C-peptide, and proinsulin levels during documented hypoglycemia 1, 2

Step 2: Provocative testing (if spontaneous episodes not captured)

• Mixed-meal tolerance test is more physiologic than oral glucose tolerance test 2
• Positive if hypoglycemia develops 60-180 minutes after mixed meal containing carbohydrates, fats, and proteins 2
• Important caveat: The Endocrine Society does not support OGTT for diagnosing postprandial hypoglycemia due to low specificity, but it remains commonly used because no optimal diagnostic approach exists 2

Step 3: Exclude structural causes

• Upper endoscopy to evaluate for gastric outlet obstruction, ulcers, or occult surgical changes 2
• Abdominal imaging (ultrasound or CT) to exclude pancreatic masses or other anatomic abnormalities 2, 3

Management Approach (If Dumping Confirmed)

Dietary modifications (first-line):

• Eliminate rapidly absorbable carbohydrates completely 4, 1
• Consume high-fiber and protein-rich foods instead 1
• Separate liquids from solids by at least 30 minutes 4
• Divide food intake into 4-6 small meals throughout the day 4

Pharmacologic therapy (second-line):

• Acarbose (alpha-glucosidase inhibitor) is specifically indicated for late dumping with hypoglycemia 4, 1, 5, 6
• Acarbose blunts rapid glucose absorption and prevents hyperinsulinemic response 1, 6

Refractory cases (third-line):

• Somatostatin analogues are the most effective medical therapy for refractory dumping syndrome 4, 1, 5
• However, these are expensive and have significant side effects 5
• For refractory hypoglycemia specifically, consider diazoxide or SGLT2 inhibitors based on limited evidence 5

Critical Clinical Pitfall

The absence of surgical history makes true dumping syndrome extraordinarily unlikely. 1, 2 Do not anchor on this diagnosis without exhaustively excluding insulinoma, factitious hypoglycemia, and other endocrine causes. The symptom pattern may mimic dumping, but the pathophysiology requires altered gastric anatomy to produce rapid nutrient delivery to the small intestine. 1, 7 If all alternative diagnoses are excluded and provocative testing confirms postprandial hypoglycemia with appropriate incretin and insulin responses, only then consider idiopathic postprandial hypoglycemia as a diagnosis of exclusion.