What causes intermittent diarrhea in adults?

Causes of Intermittent Diarrhea in Adults

Intermittent diarrhea in adults most commonly results from functional bowel disorders (particularly IBS), dietary triggers (FODMAPs, lactose, caffeine, alcohol), medications (especially magnesium, antihypertensives, NSAIDs), and bile acid malabsorption, though organic causes including microscopic colitis, celiac disease, and endocrine disorders must be systematically excluded. 1

Functional and Dietary Causes

Irritable Bowel Syndrome (IBS)

• IBS affects approximately 14% of the global population and is the most common cause of chronic intermittent diarrhea in patients without alarm features. 2
• Symptoms typically follow a relapsing-remitting pattern and are often triggered by food intake. 2
• However, IBS remains a diagnosis of exclusion—organic disease must be ruled out first, particularly in patients over 40 or those with any alarm features. 1

Dietary Triggers

• Excessive caffeine intake from coffee or energy drinks accelerates intestinal motility and commonly causes intermittent diarrhea. 1, 3
• Lactose intolerance from lactase deficiency (which increases with age) causes intermittent symptoms after dairy consumption. 1, 4
• FODMAPs (fermentable oligo-, di-, mono-saccharides and polyols), fructose, and sorbitol in food additives trigger osmotic diarrhea in susceptible individuals. 1

Alcohol

• Alcohol abuse causes diarrhea through direct toxic effects on intestinal epithelium, rapid gut transit, decreased disaccharidase activity, and reduced pancreatic function. 1, 3

Medication-Induced Diarrhea

Up to 4% of chronic diarrhea cases are medication-related, making this a critical and reversible cause to identify. 1, 3

Common Culprit Medications:

• Magnesium supplements are among the most frequent offenders. 1, 4
• Antihypertensives, particularly ACE inhibitors and calcium channel blockers like amlodipine. 1, 3, 4
• NSAIDs (non-steroidal anti-inflammatory drugs). 1, 3
• DPP-4 inhibitors (gliptins) used for diabetes. 1, 3
• Antibiotics (both during treatment and post-treatment from Clostridium difficile infection). 1
• Theophyllines, antiarrhythmics, and antineoplastic agents. 1, 3

Bile Acid Malabsorption

• Bile acid diarrhea typically occurs after meals and follows a relapsing-remitting pattern, making it a key consideration in intermittent diarrhea. 1
• This condition is particularly common after terminal ileum resection but can occur idiopathically. 1
• All patients with persistent undiagnosed chronic diarrhea should be investigated for bile acid diarrhea with SeHCAT or serum 7-alpha-hydroxy-4-cholesten-3-one testing. 1

Microscopic Colitis

• Microscopic colitis accounts for 15% of chronic diarrhea cases in older adults and presents with a relapsing-remitting course of watery diarrhea. 5
• The colonic mucosa appears completely normal on endoscopy—diagnosis requires random biopsies throughout the colon even when mucosa looks normal. 5
• This condition can cause nocturnal diarrhea and is more common in patients over 50. 3

Endocrine and Systemic Causes

Thyroid Disease

• Hyperthyroidism causes diarrhea through accelerated intestinal transit time and should be screened with TSH in all patients with chronic diarrhea. 1, 3

Diabetes Mellitus

• Diabetes causes intermittent diarrhea through multiple mechanisms: autonomic neuropathy, small bowel bacterial overgrowth, bile acid malabsorption, and medication effects (especially metformin). 1, 3

Other Endocrine Disorders

• Adrenal disease and hypoparathyroidism can predispose to diarrhea through various endocrine effects. 1

Malabsorptive Disorders

Celiac Disease

• Celiac disease affects 0.5-1% of adults and can present with intermittent symptoms, though continuous diarrhea is more typical. 4
• Iron deficiency is a sensitive indicator of small bowel enteropathy, particularly celiac disease. 1, 5
• Testing requires anti-tissue transglutaminase IgA with total IgA level. 5, 4

Pancreatic Exocrine Insufficiency

• Previous pancreatic disease should be sought in the history, as this causes fat malabsorption and intermittent symptoms. 1, 5

Post-Surgical Causes

• Extensive ileal and right colon resections lead to diarrhea from decreased absorptive surface, fat and carbohydrate malabsorption, and decreased transit time. 1
• Shorter terminal ileum resections specifically cause bile acid diarrhea. 1
• Gastric surgery and jejunoileal bypass procedures predispose to bacterial overgrowth. 1

Infectious Causes

• Recent overseas travel or exposure to infectious gastrointestinal pathogens should be explored in the history. 1
• Recent antibiotic therapy raises concern for Clostridium difficile infection, which can present with intermittent symptoms. 1

Critical Pitfalls to Avoid

• Never diagnose IBS without completing initial screening tests: complete blood count, inflammatory markers (ESR or CRP), celiac serology, thyroid function, and comprehensive metabolic panel. 1, 5
• Do not overlook medication review—this represents a reversible cause in 4% of cases and should be the first intervention. 1, 3, 4
• Abnormal inflammatory markers, anemia, or low albumin have high specificity for organic disease and mandate further investigation regardless of symptom pattern. 1, 5
• In patients over 40 or with any alarm features (blood in stool, unintentional weight loss, nocturnal symptoms, family history of colorectal cancer or IBD), colonoscopy is mandatory. 1

Initial Diagnostic Approach

Primary Care Screening Tests:

• Complete blood count (to assess for anemia). 1, 5, 4
• ESR or CRP (elevated values indicate organic disease). 1, 5, 4
• Comprehensive metabolic panel. 5, 4
• TSH (to screen for hyperthyroidism). 1, 3, 4
• Anti-tissue transglutaminase IgA with total IgA (for celiac disease). 5, 4
• Fecal calprotectin (>90% sensitivity for inflammatory bowel disease). 5

When to Refer to Gastroenterology:

• Alarm features present: blood in stool, unintentional weight loss, nocturnal diarrhea, family history of GI malignancy or IBD. 1
• Abnormal screening tests: anemia, elevated inflammatory markers, positive celiac serology. 1, 5
• Symptoms severe enough to impair quality of life despite empiric treatment. 1
• No improvement within 48 hours of medication adjustment in suspected drug-induced cases. 4