Differential Diagnoses for Steatorrhoea
Steatorrhoea has three major pathophysiologic categories: pancreatic exocrine insufficiency (most common cause of severe steatorrhoea with >13g/day faecal fat), small bowel mucosal disease, and bile acid disorders. 1
Primary Categories
1. Pancreatic Causes (Most Common for Severe Steatorrhoea)
Pancreatic exocrine insufficiency is the most frequent cause when faecal fat excretion exceeds 13 g/day (47 mmol/day). 1 This requires destruction of approximately 90% of pancreatic acinar tissue before symptoms become evident. 2
- Chronic pancreatitis (most common)
- Pancreatic carcinoma
- Cystic fibrosis
- Post-pancreatic surgery
- Pancreatic duct obstruction
2. Small Bowel Mucosal Disease
Coeliac disease is the most common small bowel enteropathy in the Western world, frequently presenting with steatorrhoea and malabsorption. 2 Prevalence ranges from 1:200 to 1:559 in European and North American populations, with higher rates in those with autoimmune diseases. 2
- Coeliac disease (screen all patients with chronic diarrhoea)
- Crohn's disease
- Tropical sprue
- Whipple's disease
- Intestinal lymphangiectasia
- Amyloidosis
- Radiation enteritis
- Lymphoma
- Giardiasis and other chronic infections 2
3. Bile Acid Disorders
- Bile acid malabsorption (particularly after terminal ileum resection <60cm)
- Post-cholecystectomy (up to 10% develop chronic diarrhoea) 2
- Small bowel bacterial overgrowth (SIBO) - causes bile acid deconjugation 2
4. Surgical Causes
Previous surgery is a critical historical factor. 1 Extensive ileal and right colon resections lead to steatorrhoea through multiple mechanisms:
- Short bowel syndrome (extensive small bowel resection)
- Gastric surgery (Billroth procedures, gastric bypass)
- Terminal ileum resection (bile acid malabsorption if <60cm; steatorrhoea if >100cm)
- Internal fistulae
- Jejunoileal bypass 2
5. Systemic and Endocrine Diseases
- Hyperthyroidism (thyrotoxicosis)
- Diabetes mellitus (autonomic neuropathy, SIBO)
- Addison's disease (adrenal insufficiency)
- Hypoparathyroidism
- Systemic sclerosis (SIBO, dysmotility) 2
6. Other Important Causes
- Alcohol abuse - mechanisms include rapid gut transit, decreased disaccharidase activity, and direct pancreatic toxicity 2, 1
- Medications - up to 4% of chronic diarrhoea cases; particularly magnesium products, NSAIDs, antihypertensives (ACE inhibitors), gliptins, theophyllines, antibiotics, antiarrhythmics, antineoplastics 1
- Lactase deficiency (disaccharidase deficiency) 2
- Mesenteric ischaemia 2
Critical Diagnostic Approach
The history must distinguish malabsorptive (steatorrhoea with bulky, pale, malodorous stools) from colonic/inflammatory diarrhoea (liquid stools with blood/mucus). 2 However, milder malabsorption may not produce obvious stool abnormalities. 2
Key Historical Red Flags:
- Duration <3 months, nocturnal symptoms, continuous (not intermittent) diarrhoea, significant weight loss - suggest organic disease 1
- Previous pancreatic disease, extensive bowel surgery, alcohol abuse 2
- Family history of coeliac, inflammatory bowel disease, or neoplasia 1
Initial Investigations Priority:
- Coeliac serology (IgA tissue transglutaminase with total IgA level) - mandatory for all chronic diarrhoea 2
- Faecal elastase-1 (<100 μg/g indicates severe pancreatic insufficiency; 100-200 μg/g mild-moderate) 1, 3
- 75SeHCAT scan or serum C4 for bile acid malabsorption (if <15% retention, treat with bile acid sequestrants) 1
- Colonoscopy with biopsies (left and right colon) to exclude microscopic colitis 1
Common Pitfalls
Do not rely on fecal fat concentration alone to differentiate pancreatic from intestinal steatorrhoea - there is significant overlap between conditions, particularly with coeliac disease. 4, 5
Selective IgA deficiency occurs in 2.6% of coeliac patients (vs 0.2% general population), causing false-negative IgA antibody tests. Check total IgA levels or add IgG serology when suspicion is high. 2
After cancer treatment (particularly pelvic radiotherapy), steatorrhoea may result from multiple coexisting conditions: pancreatic exocrine insufficiency, SIBO, and severe bile acid diarrhoea. Diagnostic testing and targeted treatment is recommended over empirical therapy. 6