What could be causing my bloating, abdominal discomfort in the lower abdomen, weight loss, and fatigue?

Differential Diagnosis and Evaluation Approach

Your constellation of symptoms—bloating, lower abdominal discomfort, weight loss, and fatigue—requires urgent evaluation to exclude serious organic disease before considering functional disorders, as weight loss is an alarm feature that mandates comprehensive workup. 1, 2

Immediate Red Flag Assessment

The presence of weight loss (especially >10%) combined with bloating and fatigue constitutes an alarm symptom that necessitates investigation for:

• Malignancy (particularly ovarian cancer in women over 50, colorectal cancer, or small cell carcinoma) 3, 1
• Inflammatory bowel disease (especially with family history) 3, 1
• Celiac disease (screen with anti-tissue transglutaminase antibodies) 3
• Severe intestinal dysmotility disorders including chronic intestinal pseudo-obstruction 3
• Paraneoplastic syndromes (thymoma, small cell lung cancer with anti-neuronal antibodies) 3

Essential Initial Workup

Laboratory Testing

• Complete blood count (to assess for anemia suggesting GI bleeding or malabsorption) 3, 1
• Comprehensive metabolic panel including electrolytes, renal function, liver function 3
• Thyroid function tests (hypothyroidism affects GI motility) 3
• Celiac serology (anti-tissue transglutaminase) 3
• Fasting glucose or HbA1c (diabetes can cause gastroparesis and dysmotility) 3
• Nutritional markers if weight loss is significant: vitamins A, D, E, B12, folate, iron, ferritin, albumin 3

Imaging Studies

• Abdominal imaging (ultrasound, CT, or MRI) to exclude structural abnormalities, masses, or bowel obstruction 3, 2
• Plain abdominal radiograph can identify dilated bowel loops suggesting pseudo-obstruction or severe dysmotility 3
• Chest X-ray if paraneoplastic syndrome suspected (thymoma, lung malignancy) 3

Algorithmic Diagnostic Approach Based on Clinical Features

If Constipation is Present

• Apply Rome IV criteria to determine if this represents IBS with constipation or functional constipation 3
• Perform digital rectal examination to assess for pelvic floor dyssynergia 1, 2
• Consider anorectal manometry if straining with soft stool or need for digital disimpaction 3, 2

If Nausea and Vomiting are Present

• Rule out gastroparesis with gastric emptying studies 3
• Consider small bowel manometry if severe dysmotility suspected 3

If Symptoms Worsen After Meals

• Trial dietary restriction for 2 weeks eliminating lactose, fructose, and high-FODMAP foods (most cost-effective initial approach) 3
• If refractory, proceed to hydrogen breath testing for carbohydrate malabsorption 3
• Fructose intolerance affects 60% of patients with functional GI disorders, lactose intolerance 51% 3

If Small Intestinal Bacterial Overgrowth (SIBO) Risk Factors Present

• Perform glucose or lactulose hydrogen breath testing 3
• Risk factors include prior abdominal surgery, diabetes, scleroderma, chronic pancreatitis 3

Specific Conditions to Consider

Chronic Intestinal Pseudo-Obstruction (CIPO)

This presents with your exact symptom complex and requires specific evaluation:

• Myopathic form: chronic pain, distension, bloating, early satiety, nausea/vomiting, weight loss, protein-energy malnutrition 3
• Neuropathic form: severe pain after food, but distension may be absent 3
• Autoantibody testing: anti-neuronal antibodies (ANNA-1/anti-Hu), anti-CRMP-5, ganglionic AChR antibodies, anti-VGKC antibodies 3
• Connective tissue screening: anti-centromere, anti-Scl70, anti-M3R for scleroderma 3
• Mitochondrial disorders: plasma/urine thymidine and deoxyuridine if MNGIE suspected 3

Functional Disorders (Only After Excluding Organic Disease)

• Irritable bowel syndrome commonly presents with bloating, abdominal pain, and altered bowel habits, but weight loss is NOT typical 4
• Abdomino-phrenic dyssynergia (APD): paradoxical diaphragmatic contraction causing visible distension without true gas accumulation 2, 5

Critical Pitfalls to Avoid

• Do not assume functional disorder when weight loss is present—this demands organic disease exclusion 1, 2
• Do not attribute all symptoms to gas accumulation—even 10% increases in intraluminal gas can trigger severe distension in susceptible patients 2
• Do not routinely order gastric emptying studies unless nausea and vomiting are prominent features 2
• Do not start probiotics empirically—evidence does not support efficacy for bloating 2
• Recognize that normal imaging does not exclude CIPO—diagnosis often requires manometry studies 3

When to Refer for Specialized Testing

• Persistent symptoms despite initial workup warrant gastroenterology referral 3
• Small bowel manometry for suspected severe dysmotility disorders 3
• Full-thickness jejunal biopsy if myopathic or neuropathic process suspected 3
• Anorectal physiology testing with balloon expulsion for pelvic floor disorders 2

The combination of weight loss with bloating and fatigue shifts the diagnostic priority away from common functional disorders toward serious organic pathology requiring systematic exclusion before symptomatic management. 3, 1, 2