What are the causes of ileus?

Causes of Ileus

Ileus results from impaired intestinal motility due to postoperative manipulation, medications (especially opioids and anticholinergics), metabolic derangements, inflammatory conditions, and neurological disorders, with abdominal surgery being the single most common precipitating factor. 1, 2

Postoperative and Traumatic Causes

• Abdominal surgery is the leading cause of ileus, occurring through direct intestinal manipulation, inflammatory responses in the bowel wall, and exacerbation by anesthetics and postoperative opioid use 1, 2, 3
• Laparoscopic procedures cause less severe ileus compared to open surgical approaches due to reduced tissue manipulation 2
• Abdominal trauma triggers ileus through inflammatory mechanisms and disruption of neural pathways 1
• Perioperative fluid overload significantly worsens and prolongs postoperative ileus by causing intestinal edema 2

Medication-Induced Causes

• Opioids are a major iatrogenic cause, acting on μ-opioid receptors in the gastrointestinal tract to inhibit propulsive motility 1, 2, 3
• Anticholinergic medications (phenothiazines, tricyclic antidepressants) cause severe dysmotility by blocking parasympathetic stimulation 4, 1, 2
• Clozapine causes dose-dependent gastrointestinal dysmotility with potentially life-threatening episodes 4, 1
• Other culprit medications include verapamil, baclofen, buserelin, clonidine, fludarabine, phenytoin, and vincristine (directly neurotoxic) 4, 1, 2

Metabolic and Endocrine Causes

• Electrolyte disturbances are critical reversible causes: hypokalemia, hypocalcemia, and hypomagnesemia all impair smooth muscle contractility 1, 2, 5
• Hypothyroidism reduces intestinal motility through decreased metabolic activity 4, 1, 2
• Diabetes mellitus causes autonomic neuropathy affecting gut innervation, representing the most common endocrine cause 4, 2
• Uremia, hypoparathyroidism, and Addison's disease can all precipitate ileus 1

Inflammatory and Infectious Causes

• Sepsis and systemic inflammatory response syndrome trigger ileus through inflammatory mediators that impair neuromuscular function 1, 2, 6
• Peritonitis from any source causes reflex inhibition of intestinal motility 4, 1, 2
• Clostridioides difficile infection can present with unexplained paralytic ileus, particularly in severe cases 4, 2
• Chagas' disease causes enteropathy with pseudo-obstruction and bacterial overgrowth 4, 1
• Viral infections (Epstein-Barr virus, cytomegalovirus, JC virus) have DNA isolated in myenteric plexuses of patients with visceral neuropathy 4, 1
• Lyme disease and botulism are rare reversible infectious causes 4, 1

Neurological Causes

Primary Visceral Neuropathies

• Enteric nervous system disorders directly affecting the myenteric and submucosal plexuses cause chronic dysmotility 4, 1

Secondary Neuropathies

• Diabetes mellitus is the most common cause of secondary neuropathy affecting gut motility through autonomic dysfunction 4, 2
• Parkinson's disease, multiple sclerosis, and myotonic dystrophy all cause enteric neuropathy 4, 1, 2
• Spinal cord injury and brainstem lesions disrupt extrinsic neural control of the gut 4, 1, 2
• Autonomic system degeneration impairs parasympathetic and sympathetic innervation 4, 2

Paraneoplastic and Autoimmune Causes

• Small cell lung cancer with anti-Hu antibodies causes myenteric ganglionitis with dense lymphocytic infiltration 4, 1
• Thymoma-associated dysmotility may resolve with tumor removal 4, 1
• Anti-neuronal antibodies (CRMP5/CV2, AchR, VGKC-complex) should prompt search for occult malignancy 4, 1
• Carcinoid tumors and neuroblastoma can cause paraneoplastic enteric neuropathy 4, 1
• Scleroderma and connective tissue diseases affect gut smooth muscle function 1, 7

Toxin-Related Causes

• Lead poisoning is a rare but reversible cause requiring specific chelation therapy 4, 1
• Botulism toxin impairs acetylcholine release at neuromuscular junctions 4, 1

Vascular Causes

• Mesenteric ischemia damages intestinal muscle and nerves, causing both acute ileus and chronic dysmotility 1

Critical Pitfalls to Avoid

• Do not miss mechanical obstruction masquerading as ileus: always obtain CT imaging with IV contrast to identify transition points, volvulus, or strangulation 4, 8
• Monitor intra-abdominal pressure when it exceeds 15 mmHg to prevent abdominal compartment syndrome, which occurs in up to 20% of critically ill patients 2, 6
• Recognize that leukocytosis >20×10⁹/L in the context of ileus should raise suspicion for C. difficile infection or impending perforation 4
• Avoid perpetuating ileus by continuing opioids and anticholinergics when alternative pain management strategies exist 2, 3
• Distinguish acute reversible ileus (resolves in days) from chronic intestinal pseudo-obstruction (>6 months duration requiring nutritional support) as management differs fundamentally 4, 7