What are the causes of ileus?

Causes of Ileus

Ileus is a functional obstruction of the bowel characterized by the failure to propel luminal contents in the absence of a mechanical obstructing lesion, resulting in symptoms similar to intestinal obstruction such as colicky abdominal pain, nausea, vomiting, and abdominal distension. 1

Postoperative/Post-traumatic Causes

• Abdominal surgery is the most common cause of ileus (postoperative ileus), resulting from manipulation during surgery, anesthetics, and opioid use 2, 1
• Trauma, especially abdominal trauma, can lead to ileus through inflammatory mechanisms and neural disruption 1, 3

Inflammatory/Infectious Causes

• Sepsis and systemic inflammatory response syndrome can cause ileus through inflammatory mediators 1, 4
• Peritonitis from any cause can trigger ileus 3
• Intestinal inflammation due to inflammatory bowel disease (especially ulcerative colitis) 2
• Infections such as Chagas' disease, Lyme disease, and viral infections (Epstein-Barr virus, cytomegalovirus, JC virus) can cause ileus 2

Metabolic/Endocrine Causes

• Electrolyte disturbances, particularly hypokalemia, hypocalcemia, and hypomagnesemia 1, 3
• Endocrine disorders including hypothyroidism, diabetes mellitus, hypoparathyroidism, and Addison's disease 2, 1
• Uremia and other metabolic derangements 3

Medication-Related Causes

• Opioids are a major cause of ileus through their action on μ-opioid receptors in the gastrointestinal tract 1
• Anticholinergics (including phenothiazines and tricyclic antidepressants) 2, 1
• Other medications associated with ileus include verapamil, clozapine, baclofen, buserelin, clonidine, fludaribine, and phenytoin 2
• NSAIDs can exacerbate ileus, particularly in patients with inflammatory bowel disease or after surgery 2

Neurological Causes

• Primary visceral neuropathies affecting the enteric nervous system 2
• Secondary neuropathies as part of generalized neurological disorders:
  • Parkinson's disease 2
  • Multiple sclerosis 2
  • Autonomic neuropathy (often diabetic) 2
  • Spinal cord injury 2
  • Brainstem lesions 2

Autoimmune/Paraneoplastic Causes

• Paraneoplastic syndromes, particularly associated with small cell lung cancer, thymoma, neuroblastoma, and carcinoid tumors 2
• Autoimmune disorders with anti-neuronal antibodies (anti-Hu, CRMP5, AchR) 2
• Scleroderma and other connective tissue diseases affecting gut motility 3

Toxin-Related Causes

• Lead poisoning 2
• Botulism 2

Vascular Causes

• Mesenteric ischemia can cause ileus through damage to the intestinal muscle and nerves 2
• Intestinal dilatation from any cause can increase intraluminal pressure, compromising microcirculation and worsening ileus 4, 5

Complications and Clinical Significance

• Ileus can lead to bacterial overgrowth with potential bacterial translocation and systemic infection 4
• Severe ileus may progress to increased intra-abdominal pressure and abdominal compartment syndrome, affecting multiple organ systems 4
• Fluid sequestration in the bowel lumen can lead to significant dehydration and electrolyte imbalances 5

Diagnostic Approach

• Clinical presentation includes abdominal distension, absence of bowel sounds, nausea, vomiting, and lack of flatus or bowel movements 1
• Radiological findings typically show dilated bowel loops with air-fluid levels but no transition point 1
• CT scan is the most useful imaging modality to differentiate between ileus and mechanical obstruction 1

Understanding the specific cause of ileus is crucial for appropriate management, as treatment should target the underlying etiology while providing supportive care.