Aetiology

Steatorrhoea occurs due to impaired fat digestion in patients with pancreatic enzyme deficiencies, or as a consequence of impaired fat absorption. Both bile salt deficiency and small intestinal disease can lead to fat malabsorption.

Pancreatic insufficiency steatorrhoea

Chronic inflammation of the pancreas (chronic pancreatitis) leads to cumulative loss of lipase-producing acinar cells. Steatorrhoea occurs late in the disease process and is a manifestation of severe exocrine deficiency. Loss of >90% of pancreatic function is required before steatorrhoea becomes clinically apparent.[4][5]​​​ Once steatorrhoea develops, it has 100% specificity for pancreatic exocrine insufficiency, but only 38% sensitivity.[6]​​

The causes of cumulative injury include:[7]​​

  • Alcohol excess

  • Idiopathic causes

  • Pancreatic duct obstruction

  • Trypsinogen gene mutations (hereditary pancreatitis)

  • Cystic fibrosis

  • Autoimmune pancreatitis.

Although alcohol and idiopathic causes have traditionally accounted for the majority (>80%) of cases of chronic pancreatitis, identification of mutations in genes that encode for pancreatic enzymes and protease inhibitors provide insights into the pathophysiology of a small proportion of 'idiopathic' cases.[8]​​

Acute pancreatitis

Pancreatic exocrine insufficiency (EPI) may occur following severe acute pancreatitis. One meta-analysis reported EPI prevalence of 62% among patients with acute pancreatitis (all severity grades) during their initial admission.[9]​ Risk for EPI was higher among patients with pancreatic necrosis and alcohol aetiology. Prevalence decreased during recovery.[9]

Bile salt deficiency steatorrhoea

Patients with primary or secondary biliary cholangitis, or prolonged biliary obstruction, experience impaired excretion of bile salts (bile acids) into the duodenum. Reduced release of bile salts into the jejunal lipid emulsion impairs the micelle formation necessary for translocation of lipids into the intestinal cells. As with pancreatic disease, significant loss of bile salt output is necessary for steatorrhoea to occur.

Causes of bile salt steatorrhoea include:

  • Primary biliary cholangitis (PBC)

  • Primary sclerosing cholangitis (PSC)

  • Bacterial overgrowth

  • Terminal ileum Crohn's disease

  • Ileal resection

  • Primary bile acid malabsorption

PBC and PSC reduce the release of bile salts into the duodenum. Bacterial overgrowth inhibits re-uptake of bile salts by increasing the proportion of unconjugated bile acids.[10] Resection or inflammation of the terminal ileum also impairs the normal re-uptake of bile acids into the enterohepatic circulation, thus reducing the overall bile salts available.[11]​ Although such bile acid malabsorption initially causes watery diarrhoea, severe loss leads to steatorrhoea. Patients with PBC may also have bacterial overgrowth and pancreatic exocrine insufficiency that contribute to steatorrhoea.[12]​ Fat malabsorption usually occurs with concurrent malnutrition in patients with cirrhosis of any cause.[13]​​

Malabsorption steatorrhoea

Diseases of the small intestine cause impaired function of the surface intestinal epithelium, leading to impaired global absorption of lipids, carbohydrates, proteins, and minerals. Clinical features in patients with malabsorption and diarrhoea include steatorrhoea, liquid stools, nutritional deficiency, and weight loss. Steatorrhoea is rarely the predominant symptom; approximately 50% of patients with diarrhoeal disease have abnormal stool fat levels, but only half of these describe steatorrhoea.[14]​​[15]​​

There are numerous causes for malabsorption, including:​[16]​​[17][18]​​​​​

  • Coeliac disease

  • Surgical resection/bypass

  • Giardia infection

  • HIV-enteropathy/AIDS infections

  • Lymphoma

  • Crohn's disease

  • Whipple's disease

  • Intestinal ischaemia

  • Amyloidosis

  • Bacterial overgrowth.

Miscellaneous causes of steatorrhoea

Several other aetiologies have been reported as case reports or case series:[19][20][21]​​[22][23]​​[24]​​[25]

  • Post-gastrectomy

  • Zollinger-Ellison syndrome

  • Graves disease

  • Diarrhoea-predominant irritable bowel syndrome

  • Non-absorbable fat substitutes (olestra)

  • Meclofenamate sodium

  • Lipase inhibitors - for example, tetrahydrolipstatin (orlistat)

  • Graft-versus-host disease (pancreatic involvement)

  • Surgical resection of the pancreas such as Whipple's operation, pylorus-preserving pancreatectomy, or total pancreatectomy for benign or malignant neoplasms.

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