What is the most probable differential diagnosis (DDX) for gastric pain in the lower abdomen with acidity and constipation?

Differential Diagnosis for Lower Abdominal Pain with Acidity and Constipation

Most Probable Diagnosis: Functional Dyspepsia with Overlapping Irritable Bowel Syndrome (IBS-C)

The most probable diagnosis is functional dyspepsia overlapping with constipation-predominant IBS, as up to 50% of functional dyspepsia patients report coexisting functional bowel disorders including functional constipation, and these conditions share common pathophysiologic mechanisms along the gut-brain axis 1.

Primary Differential Considerations

Functional Dyspepsia with IBS Overlap

• Functional dyspepsia presents with epigastric pain or burning (the "acidity" symptom) that does not necessarily occur after meals and may even improve with eating 2.
• Functional constipation commonly overlaps with functional dyspepsia, with patients reporting two distinct types of abdominal pain—one related to defecation (lower abdomen) and one unrelated (epigastric) 1.
• The overlap between these conditions occurs more frequently than expected by chance and represents a spectrum of disorders of gut-brain interaction 1.

Gastroesophageal Reflux Disease (GERD)

• GERD affects 42% of Americans monthly, presenting with heartburn, acid regurgitation, and epigastric pain that can extend to lower abdominal discomfort 3.
• Approximately one-third of functional dyspepsia patients have coexisting GERD symptoms, with 63-66% experiencing both epigastric pain and heartburn simultaneously 1, 4.
• The burning sensation starting in the epigastrium but radiating upward to the chest helps differentiate GERD from dyspepsia 1.

Peptic Ulcer Disease (PUD)

• PUD has an incidence of 0.1-0.3% and accounts for approximately 10% of upper gastrointestinal symptoms 1.
• Gastric ulcer pain occurs immediately after eating and is localized in the epigastrium, while duodenal ulcer pain occurs several hours after eating and is often relieved by food 2.
• Complications occur in 2-10% of cases, with perforation carrying up to 30% mortality if treatment is delayed 1, 3.

Critical Red Flags Requiring Immediate Evaluation

Alarm Features Mandating Urgent Investigation

• Weight loss in patients ≥25 years with dyspepsia requires 2-week wait endoscopy 1.
• Age >40 years from areas at increased risk of gastric cancer or with family history of gastro-oesophageal malignancy warrants urgent endoscopy 1.
• Sudden severe epigastric pain with fever, abdominal rigidity, and absent bowel sounds suggests perforation requiring emergent surgical consultation 3, 4.
• Rectal bleeding, nocturnal symptoms, or anemia exclude functional disorders and mandate investigation 1.

Diagnostic Approach

Initial Assessment in Primary Care

• A working diagnosis of functional dyspepsia with IBS can be safely made in primary care based on typical symptoms, normal physical examination, and absence of alarm features, confirmed by observation over time 1.
• The diagnosis is more likely if the patient is female, aged <45 years, with symptom duration >2 years, and has attended frequently with non-gastrointestinal symptoms 1.

Baseline Investigations

• Full blood count in patients aged ≥25 years to exclude anemia 1.
• Coeliac serology (tissue transglutaminase antibody) in patients with overlap IBS-type symptoms, as celiac disease prevalence is 2.1% in IBS patients vs 0.8% in controls 1.
• H. pylori breath or stool testing, as H. pylori is the main cause of peptic ulcers not associated with NSAIDs 1.

When to Consider Endoscopy

• Patients ≥55 years with new-onset dyspepsia should undergo endoscopy to exclude malignancy 1.
• Treatment-resistant dyspepsia in patients ≥25 years warrants consideration of non-urgent endoscopy 1.
• Endoscopy adds little value in young patients without alarm features who respond to empirical therapy 1.

Management Algorithm

First-Line Empirical Treatment

• For patients ≤55 years without alarm features, initiate H. pylori test-and-treat strategy followed by acid suppression if symptoms persist 1.
• Proton pump inhibitors (PPIs) are the drug class of choice for acid suppression, prescribed for 4-8 weeks empirically 1.
• PPI therapy achieves healing rates of 80-90% for duodenal ulcers and 70-80% for gastric ulcers 3.

Addressing Constipation Component

• Dietary modification is the initial approach for managing functional bowel symptoms and benefits the majority of patients 1.
• Increased fiber intake, adequate hydration, and regular physical activity should be recommended 1.
• Avoid laxative abuse, which can be detected through urinary screening if suspected 1.

Patient Education

• Establishing an empathic doctor-patient relationship and explaining the diagnosis as a disorder of gut-brain interaction reduces healthcare utilization and improves quality of life 1.
• Explain that functional dyspepsia and IBS are real conditions with underlying pathophysiology involving visceral hypersensitivity, altered gut motility, and brain-gut axis dysfunction 1.
• Discuss common symptom triggers including diet, stress, and emotional responses 1.

Common Pitfalls to Avoid

• Never assume benign functional disease in patients with alarm features (weight loss, persistent vomiting, anemia, dysphagia) without investigation, as gastric cancer is now the most common cause of gastric outlet obstruction in adults 5, 3.
• Do not dismiss cardiac causes in patients with epigastric pain regardless of age, as myocardial infarction can present atypically with epigastric pain as the primary manifestation 3, 4.
• Avoid performing extensive investigations in young patients without alarm features, as this reinforces illness behavior and increases healthcare costs without improving outcomes 1.
• Do not overlook the possibility of medication-induced symptoms—NSAIDs worsen peptic ulcer disease and should be avoided 5, 3.
• Recognize that true food allergy is rare, but many patients believe food intolerances cause symptoms; lactose intolerance occurs in only 10% of IBS patients and lactose exclusion rarely cures IBS 1.

Follow-Up Strategy

• Patients who respond to H. pylori eradication or PPI therapy can be managed without further investigation 1.
• If symptoms persist despite empirical therapy in patients <55 years without alarm features, consider non-urgent endoscopy 1.
• Reassess for development of alarm features at each visit, as these mandate investigation regardless of initial diagnosis 1.