What is the differential diagnosis and management approach for abdominal distension?

Abdominal Distension: Differential Diagnosis and Management

Abdominal distension requires a systematic evaluation prioritizing life-threatening mechanical obstruction and bowel ischemia first, followed by assessment for paralytic ileus, chronic intestinal dysmotility, and functional disorders, with initial management directed by the presence or absence of peritoneal signs and hemodynamic stability.

Initial Clinical Assessment

History and Physical Examination

The focused history must elicit specific red flags and symptom patterns:

• Acute onset with severe pain, constipation, and vomiting suggests mechanical obstruction such as sigmoid volvulus, particularly in elderly, institutionalized patients on psychotropic medications 1
• Previous episodes of distension occur in 30-41% of sigmoid volvulus cases 1
• Asymmetric gaseous distention with emptiness of the left iliac fossa is pathognomonic for sigmoid volvulus, though challenging to detect 1
• Complete absence of bowel sounds indicates paralytic ileus 2
• Diminished bowel sounds with distension suggests sigmoid volvulus or other mechanical obstruction 1
• Fever, tachycardia, weight loss, and reduced bowel sounds indicate severe disease requiring urgent intervention 1

Critical pitfall: The absence of peritonitis does not exclude bowel ischemia—physical examination and lactate levels are crucial even without peritoneal signs 1.

Essential Laboratory Testing

Initial blood work must include 1:

• Complete blood count (thrombocytosis suggests chronic inflammation; leucocytosis suggests infection)
• Blood gas and lactate levels (bowel ischemia may exist despite normal lactate) 1
• Electrolytes and renal function (vomiting and dehydration cause renal insufficiency) 1
• C-reactive protein (CRP >10 mg/L predicts increased surgical risk in colitis) 1
• Liver function tests 1

Stool testing is mandatory to exclude infectious causes, specifically C. difficile toxin 1. For patients with ileus unable to produce stool, perirectal swab PCR provides an acceptable alternative 2.

Imaging-Based Diagnostic Algorithm

Plain Abdominal Radiographs (First-Line)

Order immediately in all patients with acute abdominal distension 1:

• "Coffee bean sign" projecting toward the upper abdomen confirms sigmoid volvulus 1
• "Northern exposure sign" (coffee bean above transverse colon) is pathognomonic 1
• Chest radiograph detects free air from perforation 1

CT Imaging with IV Contrast (Second-Line)

Obtain urgently when 1:

• Plain radiographs are non-diagnostic
• Bowel ischemia or perforation is suspected
• Mechanical obstruction needs confirmation (90% accuracy) 2

CT provides critical information about bowel viability and helps differentiate mechanical from functional obstruction 1.

Differential Diagnosis Framework

Life-Threatening Causes (Exclude First)

1. Sigmoid Volvulus 1, 3

   • Classic triad: abdominal pain, constipation, vomiting
   • Coffee bean sign on radiograph
   • Empty rectum on digital examination
   • Requires immediate decompression or surgery

2. Bowel Ischemia/Perforation 1, 2

   • Elevated lactate (though may be normal early)
   • Peritoneal signs, fever, tachycardia
   • Free air on imaging
   • Requires emergency surgical consultation

Acute Non-Mechanical Causes

1. Paralytic Ileus 2
   • Complete absence of bowel sounds (hallmark finding)
   • Occurs in ~65% with abdominal distension
   • Causes: sepsis, peritonitis, strongyloidiasis in immunocompromised, medications (opioids, anticholinergics)
   • Conservative management: nasogastric decompression, electrolyte correction, minimize opioids

Chronic/Subacute Causes

1. Chronic Intestinal Pseudo-Obstruction (CIPO) 1, 4, 5

   • Recurrent nausea, vomiting, pain, and distension
   • Marked small bowel gas pooling on CT 5
   • Consider channelopathies if family history of sudden cardiac death 4
   • Screen for mitochondrial disorders (present in 19% of adult CIPO) 4

2. Functional Bloating/Distension 6, 7, 8

   • Rome IV criteria: feeling of fullness ± measurable girth increase
   • Often overlaps with IBS, functional dyspepsia, constipation
   • Etiologies: dietary (FODMAPs, lactose), SIBO, visceral hypersensitivity, abdomino-phrenic dyssynergia
   • Diagnosis of exclusion after negative workup

3. Inflammatory Bowel Disease 1

   • Abdominal distension with diarrhea, blood per rectum
   • Elevated CRP and fecal calprotectin
   • Requires endoscopy with biopsy for diagnosis

4. Constipation-Related Distension 1

   • Digital rectal examination reveals impacted stool
   • Abdominal examination shows palpable stool
   • Responds to laxatives and disimpaction

Management Algorithm

Acute Presentation with Peritoneal Signs or Hemodynamic Instability

Immediate actions 1, 2:

1. NPO status, IV fluid resuscitation
2. Nasogastric tube for decompression
3. Broad-spectrum antibiotics if peritonitis suspected (4-7 day course) 2
4. Emergency surgical consultation
5. Serial lactate monitoring

Acute Presentation Without Peritoneal Signs

For suspected sigmoid volvulus 1:

• Attempt endoscopic decompression if no perforation/ischemia
• Surgical consultation for definitive management

For paralytic ileus 2:

• Conservative management: NGT decompression, correct electrolytes, minimize opioids
• Prokinetic agents (metoclopramide) and peripheral mu-opioid antagonists
• Antibiotics only if infection/peritonitis present

Chronic/Recurrent Distension

Stepwise approach 6, 7, 8:

1. Dietary modification trial (4-6 weeks each):

   • Low FODMAP diet
   • Lactose-limiting diet
   • Small, frequent meals

2. Pharmacologic options based on predominant symptom:

   • Constipation-predominant: secretagogues (linaclotide), osmotic laxatives
   • Pain-predominant: antispasmodics (otilonium bromide, peppermint oil) 8
   • SIBO suspected: rifaximin trial 8
   • Severe symptoms: neuromodulators (SNRIs, TCAs, buspirone) 8

3. Probiotics for dysbiosis 8

4. Biofeedback for abdomino-phrenic dyssynergia 8

5. Psychological interventions: CBT, hypnotherapy for IBS overlap 8

Severe Intestinal Dysmotility

For patients with CIPO or severe dysmotility 1, 4:

• Avoid medications that worsen motility: opioids, anticholinergics, calcium channel blockers 4
• Nutritional support escalation: oral supplements → gastric feeding → jejunal feeding → parenteral nutrition (only if malnourished) 1
• Do not escalate to parenteral nutrition in pain-predominant presentations without objective malnutrition—this risks iatrogenesis 4
• Screen for mitochondrial disorders and channelopathies 4
• Venting gastrostomy may reduce vomiting but has complications 1

Critical Pitfalls to Avoid

• Never assume absence of peritonitis means absence of ischemia—lactate and serial examinations are essential 1
• Do not attribute chronic symptoms solely to functional disorders without excluding channelopathies, especially with family history of sudden cardiac death 4
• Avoid high-dose opioids and cyclizine in chronic dysmotility—consider narcotic bowel syndrome and supervised withdrawal 1
• Do not perform unnecessary surgery in patients with chronic dysmotility without clear mechanical obstruction 1
• Recognize that rales are absent in most chronic heart failure patients despite elevated filling pressures—jugular venous distension is the most reliable sign of volume overload 1