What causes alternating constipation and diarrhea?

Causes of Alternating Constipation and Diarrhea

Irritable Bowel Syndrome (IBS) is the most common cause of alternating constipation and diarrhea, characterized by abdominal pain or discomfort associated with changes in bowel habits without structural abnormalities.

Primary Causes

1. Irritable Bowel Syndrome (IBS)

• IBS with alternating bowel habits (IBS-A): Approximately 19-24% of IBS patients experience alternating constipation and diarrhea 1
• Most patients with alternating symptoms consider themselves primarily constipated 1
• Clinical manifestations in alternating IBS are similar to constipation-predominant IBS but with added defecatory urgency 1
• Patients with alternating IBS report greater abdominal discomfort/pain and more frequent physician visits than other IBS subtypes 1

2. Fecal Impaction or Partial Bowel Obstruction

• Can manifest as alternating constipation and diarrhea 2
• Liquid stool may pass around the impacted fecal matter, creating the appearance of diarrhea

3. Medication-Related Causes

• Laxative abuse can lead to alternating patterns 2
• Certain medications can disrupt normal bowel function

Secondary Causes

1. Gastrointestinal Neuropathies

• Diabetic autonomic neuropathy can affect any section of the gastrointestinal tract 2
• Constipation is the most common lower-gastrointestinal symptom but can alternate with episodes of diarrhea 2

2. Other Conditions

• Small intestinal bacterial overgrowth
• Post-surgical changes (especially after bowel resection)
• Malabsorption disorders
• Bile acid malabsorption 3

Diagnostic Approach

Initial Assessment

1. Evaluate for IBS: Apply Rome criteria (abdominal pain/discomfort, bloating, and change in bowel habits for at least 6 months) 4
2. Screen for red flags:
   • Rectal bleeding
   • Anemia
   • Nighttime pain
   • Weight loss
   • Recent onset in older adults (>50 years)

Diagnostic Testing

• For patients with suspected IBS without red flags, limited testing is typically needed 4
• When indicated, consider:
  • Complete blood count
  • Fecal occult blood test
  • Flexible sigmoidoscopy
  • Lactose intolerance evaluation 5
  • Stool studies to rule out infectious causes

Management Strategies

For IBS with Alternating Symptoms

1. Dietary modifications:

   • Avoid fermentable carbohydrates (FODMAPs) for patients with bloating 4
   • Eliminate lactose-containing products if lactose intolerant 2
   • Avoid high-osmolar dietary supplements 2

2. Pharmacologic treatment:

   • For constipation phases:

     • Fiber supplementation
     • Osmotic laxatives
     • Lubiprostone or linaclotide for constipation-predominant phases 4

   • For diarrhea phases:

     • Loperamide (initial dose of 4 mg followed by 2 mg every 4 hours or after every unformed stool, not exceeding 16 mg/day) 2
     • Antispasmodics during acute episodes

   • For long-term management:

     • Tricyclic antidepressants (e.g., amitriptyline 10-75 mg at bedtime) 2, 4
     • Selective serotonin reuptake inhibitors
     • Peppermint oil and probiotics may provide benefit 4

For Fecal Impaction

• Disimpaction followed by maintenance therapy to prevent recurrence
• Address underlying causes

For Diabetic Autonomic Neuropathy

• Optimize glycemic control to prevent progression 2
• Symptomatic treatment for bowel symptoms

Special Considerations

Elderly Patients

• Higher risk for fecal impaction presenting as alternating symptoms 2
• More susceptible to medication side effects
• May have multiple contributing factors

Patients with Diabetes

• Annual screening for diabetic neuropathy is recommended 2
• Gastrointestinal neuropathies should be suspected in individuals with erratic glucose control 2

When to Refer to a Specialist

• Persistent symptoms despite appropriate management
• Presence of red flag symptoms
• Diagnostic uncertainty
• Need for advanced therapeutic interventions

Remember that alternating constipation and diarrhea is most commonly due to IBS, but a thorough evaluation is necessary to exclude other causes, especially in patients with red flag symptoms or those who don't respond to initial management.