What causes yellow greasy stool in a patient with pancreatitis?

Yellow Greasy Stool in Pancreatitis: Pathophysiology

Yellow greasy stool in pancreatitis results from pancreatic exocrine insufficiency causing fat maldigestion—specifically, the destruction of pancreatic acinar tissue leads to insufficient secretion of pancreatic lipase, preventing normal breakdown and absorption of dietary fats in the small intestine. 1, 2

Mechanism of Steatorrhea Development

Progressive pancreatic destruction is the fundamental cause:

• Chronic pancreatitis progressively destroys both islet cells and acinar tissue, with the acinar tissue responsible for secreting digestive enzymes including lipase, which is essential for fat digestion 1
• Approximately 90% of pancreatic acinar tissue must be destroyed before clinical symptoms of malabsorption become evident, though this traditional teaching may overestimate the threshold 1, 3
• When lipase secretion drops to <10% of normal values, severe fat maldigestion occurs, resulting in steatorrhea 4, 3

Why Stools Become Yellow and Greasy

The characteristic appearance reflects undigested fat:

• Steatorrhea is characterized by bulky, pale/light-colored (yellow), malodorous, and floating stools due to excess fat content 2
• The greasy appearance results from undigested dietary fats passing through the gastrointestinal tract without proper emulsification and absorption 5
• Fecal fat exceeding 13 g/day (47 mmol/day) is considered severe steatorrhea and is most frequently caused by pancreatic exocrine insufficiency 2

Clinical Context and Timing

Steatorrhea appears late in chronic pancreatitis:

• In chronic pancreatitis, symptoms typically develop 10-15 years after initial symptoms and coincide with the appearance of pancreatic calcifications 4, 6
• The malabsorption is more accurately termed maldigestion rather than malabsorption, since the problem originates from inadequate enzyme secretion rather than intestinal absorptive defects 1
• Pancreatic steatorrhea presents with bulky, pale, and malodorous stools, distinguishing it from intestinal causes which typically present with liquid stools and blood or mucus 4

Associated Complications

Fat malabsorption leads to multiple deficiencies:

• Deficiencies in fat-soluble vitamins (A, D, E, K) develop even in mild to moderate pancreatic insufficiency 2
• Weight loss commonly accompanies steatorrhea due to the combination of poor dietary intake, malabsorption, and increased resting energy expenditure 3
• Associated symptoms include flatulence, bloating, dyspepsia, urgency to pass stools, and cramping abdominal pain 2

Diagnostic Confirmation

Fecal elastase-1 is the preferred initial test:

• FE-1 is the most commonly used indirect pancreatic function test, being simple, noninvasive, and relatively inexpensive 2
• FE-1 <100 μg/g is consistent with exocrine pancreatic insufficiency, and <50 μg/g is most reliable for severe EPI 2, 4
• Clinical assessment of steatorrhea by stool inspection alone is unreliable and requires objective testing 2

Important Clinical Pitfall

Visible steatorrhea requires severe disease:

• Visible steatorrhea usually requires moderate fat in the diet and is typically not expected unless there is severe or decompensated pancreatic exocrine insufficiency 2
• Steatorrhea may not be clinically apparent in milder forms of malabsorption, meaning absence of obvious greasy stools does not exclude pancreatic insufficiency 2