What are the causes of an ileus?

Causes of Ileus

Ileus results from multiple etiologies, with postoperative manipulation being the most common cause, followed by medications (especially opioids and anticholinergics), metabolic derangements (particularly electrolyte abnormalities), and systemic inflammation from sepsis or peritonitis. 1, 2

Postoperative and Traumatic Causes

• Abdominal surgery is the leading cause of ileus, occurring through direct intestinal manipulation during the operation, inflammatory responses in the bowel wall, and exacerbation by anesthetics and postoperative opioid use 3, 2
• Intraoperative manipulation causes panenteric inflammation that directly impairs intestinal motility 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, 2
• Perioperative fluid overload is a major preventable cause—excess crystalloid administration causes intestinal edema that significantly worsens and prolongs postoperative ileus 3, 2

Medication-Induced Causes

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

Metabolic and Endocrine Causes

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

Inflammatory and Infectious Causes

• Sepsis and systemic inflammatory response syndrome trigger ileus through inflammatory mediators that impair neuromuscular function 1, 2
• Peritonitis from any source causes reflex inhibition of intestinal motility 3, 1, 2
• Clostridioides difficile infection can present with unexplained paralytic ileus, particularly in severe cases 2
• Chagas disease causes enteropathy with pseudo-obstruction and bacterial overgrowth 1, 2
• Viral infections (Epstein-Barr virus, cytomegalovirus, JC virus) have DNA isolated in myenteric plexuses of patients with visceral neuropathy 1, 2
• Lyme disease and botulism are rare reversible infectious causes 1, 2

Neurological Causes

• Enteric nervous system disorders directly affecting the myenteric and submucosal plexuses cause chronic dysmotility 2
• Parkinson's disease, multiple sclerosis, and myotonic dystrophy all cause enteric neuropathy 1, 2
• Spinal cord injury and brainstem lesions disrupt extrinsic neural control of the gut 1, 2
• Autonomic system degeneration impairs parasympathetic and sympathetic innervation 2

Paraneoplastic and Autoimmune Causes

• Small cell lung cancer with anti-Hu antibodies causes myenteric ganglionitis with dense lymphocytic infiltration 2
• Thymoma-associated dysmotility may resolve with tumor removal 2
• Anti-neuronal antibodies (anti-Hu, CRMP5, AchR) should prompt search for occult malignancy 1, 2
• Carcinoid tumors and neuroblastoma can cause paraneoplastic enteric neuropathy 1, 2
• Scleroderma and connective tissue diseases affect gut smooth muscle function 1, 2

Toxin-Related Causes

• Lead poisoning is a rare but reversible cause requiring specific chelation therapy 1, 2
• Botulism toxin impairs acetylcholine release at neuromuscular junctions 1, 2

Vascular Causes

• Mesenteric ischemia damages intestinal muscle and nerves, causing both acute ileus and chronic dysmotility 1, 2

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 2
• Monitor intra-abdominal pressure when it exceeds 15 mmHg to prevent abdominal compartment syndrome 2
• Recognize that leukocytosis in the context of ileus should raise suspicion for C. difficile infection or impending perforation 2
• Avoid perpetuating ileus by continuing opioids and anticholinergics when alternative pain management strategies exist 5, 2
• Distinguish acute reversible ileus from chronic intestinal pseudo-obstruction as management differs fundamentally 2