Aetiology
Classification by location
The following aetiological classification may be practical and helpful for the evaluation of patients with chronic abdominal pain, although pain may arise from a vast number of causes in any system (only the more common causes are covered in further detail):
I. Pain originating from the abdominal viscera (visceral abdominal pain)
Gastrointestinal (GI) tract: hollow organs
Oesophagus: oesophagitis (e.g., GORD); drug-induced (e.g., bisphosphonate, erythromycin); motility disorders (e.g., atypical achalasia); oesophageal cancer
Stomach: chronic gastritis (e.g., Helicobacter pylori); drug/alcohol-induced; peptic ulcer disease; gastric cancer
Small bowel: inflammation (e.g., Crohn's disease); drug-induced (e.g., aspirin, non-steroidal anti-inflammatory drug [NSAID]); subacute obstruction (e.g., volvulus, intussusception)
Large bowel: inflammation (e.g., ulcerative colitis, Crohn's colitis, infectious gastroenteritis); subacute obstruction (e.g., volvulus, tumour); colorectal cancer
GI tract: solid organs
Liver: hepatocellular carcinoma, metastasis, abscesses
Pancreas: chronic pancreatitis, pancreatic cysts/pseudocysts
Gallbladder: cholecystitis, cholelithiasis
Urogenital tract
Kidneys/ureter/bladder: nephrolithiasis, pyelonephritis, perinephric abscess
Gynaecological diseases within the abdomen: endometriosis
Abdominal vasculature
Chronic mesenteric ischaemia/intestinal ischaemia/abdominal angina
Superior mesenteric syndrome
II. Pain referred from an extra-abdominal source (referred abdominal pain)
Pelvis
Chronic pelvic pain (CPP) (e.g., interstitial cystitis, endometriosis, adhesions, urethral syndrome, changes or dysfunction of the pelvic muscles)[19]
Female genitalia and reproductive organs (e.g., pelvic inflammatory disease [PID], endometriosis, ovarian cystic diseases, gynaecological malignancies)
Male genitalia and reproductive organs (e.g., prostatitis, prostate cancer, epididymitis, intermittent/recurrent torsion of testicle)[20]
Chest/thorax
Lungs (e.g., malignancy)
Pleura and chest wall
Musculoskeletal
Abdominal wall (e.g., abdominal cutaneous nerve entrapment syndrome, abdominal wall hernia)[21]
Spine (e.g., radiculitis)
Neurogenic causes
Herpes zoster
III. Systemic/metabolic causes
Coeliac disease
Lactose intolerance/lactase deficiency
Drugs: narcotics, non-dihydropyridine calcium-channel blockers, vitamins, mineral supplements (e.g., iron, calcium, magnesium, and aluminium)
Porphyria: acute intermittent
Heavy metal poisoning: lead/arsenic poisoning
Familial Mediterranean fever
Paroxysmal nocturnal haemoglobinuria
IV. Neurogastroenterology
Irritable bowel syndrome
Functional dyspepsia
Centrally mediated abdominal pain syndrome (formerly functional abdominal pain syndrome)
Narcotic bowel syndrome
Abdominal migraine.
Classification by pathophysiology
In addition to categorisation by organ or system involvement, the underlying pathophysiology should also be considered.
1. Mechanical obstruction
Intestinal, urinary, or biliary tract obstruction usually presents acutely. Partial or intermittent obstruction may take longer to recognise and lead to chronic or recurrent abdominal symptoms.
2. Rupture of hollow viscera
Usually associated with an acute presentation. However, small perforations with spontaneous sealing and resulting in the formation of local abscesses may lead to chronic abdominal pain.
3. Chronic inflammation
Can lead to symptoms of chronic abdominal pain.
Intestinal inflammation can involve different segments of the GI tract and be secondary to various aetiologies. Common examples are oesophageal inflammation due to gastro-oesophageal reflux, gastric inflammation due to Helicobacter pylori, and small and/or large bowel inflammation due to ulcerative colitis or Crohn's disease.
Inflammatory processes involving other GI organs (e.g., pancreas, liver, gallbladder) and non-GI organs (e.g., urinary bladder and kidneys) should also be considered.
4. Ischaemia
Reduction in intestinal blood flow (intestinal/mesenteric ischaemia) may be acute in onset with serious (and sometimes catastrophic) consequences; or it may be chronic, leading to chronic or recurrent GI symptoms. Most patients with chronic mesenteric ischaemia are asymptomatic due to good collateral circulation between the 3 mesenteric arteries. Symptoms arise when there is a significant occlusion of 2 of the 3 main mesenteric arteries.[22]
Chronic mesenteric ischaemia (sometimes also called intestinal angina) should be suspected mainly in older adult patients with underlying atherosclerotic vascular disease and/or a heavy smoking history who present with dull, crampy, upper/epigastric abdominal pain that usually appears within 1 hour after meals and subsides spontaneously over 2 to 3 hours. Other symptoms include nausea and vomiting, weight loss, and food aversion.
Microvascular occlusive disease in patients with sickle cell disease, small-vessel vasculitis, low-flow state, or veno-occlusive disease.
Calcification of mesenteric vessels on radiography is suggestive, but further testing with computed tomography or magnetic resonance imaging angiography is usually needed to confirm the diagnosis.[23]
5. Drugs/medications
Various drugs cause inflammation, injury, or even ulceration of the intestinal mucosa.
Examples include oesophageal inflammation due to erythromycin or bisphosphonates, and gastric or small intestine inflammation due to chronic use of aspirin or NSAIDs.
Certain drugs can cause abdominal symptoms, including pain, without overt inflammatory manifestations. Non-dihydropyridine calcium-channel blockers, such as diltiazem and verapamil, slow gut motility and lead to chronic constipation and pain. Common vitamin and mineral supplements, such as iron and calcium, can exacerbate constipation and abdominal pain, while magnesium and aluminium, in high doses, can cause loose stools, occasionally with crampy pain.
Chronic narcotic use, in addition to contributing to chronic constipation, can contribute to visceral hyperalgesia or an over-sensitive bowel. Prolonged use of narcotics, especially short-acting agents, causes a 'soar and crash' effect where temporary pain relief leads to a more sensitive intestinal tract and thus greater pain and escalating narcotic use. Chronic abdominal pain that occurs in the setting of chronic narcotic use, with or without escalating doses, and providing no relief of the pain, is known as narcotic bowel syndrome (opioid-induced gastrointestinal hyperalgesia).[24] Symptoms of narcotic bowel syndrome may improve upon withdrawal of the opioid.[25]
6. Centrally mediated disorders of gastrointestinal pain
Centrally mediated abdominal pain syndrome (CAPS) is a functional GI disorder. It refers to conditions resulting from central nervous system sensitisation with disinhibition of pain signals, rather than increased peripheral afferent excitability. Unlike irritable bowel syndrome and functional dyspepsia, pain associated with CAPS is reported to be constant and unrelated to peripheral events such as food intake or defecation.[25]
Narcotic bowel syndrome (opioid-induced GI hyperalgesia) symptoms may improve upon withdrawal of the opioid.[25]
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