How do kidney stones cause diarrhea?

How Kidney Stones Can Cause Diarrhea

Kidney stones primarily cause diarrhea in patients with jejunum-colon anastomosis following intestinal resection, where fat malabsorption leads to increased colonic oxalate absorption and subsequent stone formation, creating a cycle of gastrointestinal symptoms. 1

Mechanism of Diarrhea in Kidney Stone Patients

Intestinal Resection and Short Bowel Syndrome

• Patients with jejunum-colon anastomosis following intestinal resection have a 25% chance of developing symptomatic calcium oxalate renal stones 1
• These patients typically experience diarrhea that is malodorous and bulky due to steatorrhoea (fat malabsorption) 1

Fat Malabsorption Pathway

• Fat malabsorption is a key contributor to both kidney stone formation and diarrhea in these patients 1
• Unabsorbed fatty acids in the colon bind to calcium, leaving more free oxalate available for absorption 2
• This creates a cycle where:
  • Fat malabsorption leads to diarrhea
  • Fat malabsorption also increases colonic permeability to oxalate
  • Increased oxalate absorption leads to kidney stone formation 1, 2

Other Contributing Factors

• Increased bile salt induced colonic permeability to oxalate further exacerbates the problem 1
• Reduced bacterial degradation of oxalate in the intestine contributes to hyperoxaluria 1
• Hypocitraturia and pyridoxine or thiamine deficiency may also play roles in stone formation 1

Clinical Presentation and Management

Recognizing the Connection

• Patients with jejunum-colon anastomosis who present with both diarrhea and kidney stones should be evaluated for enteric hyperoxaluria 2
• These patients typically have calcium oxalate stones rather than other stone types 2

Dietary Management

• Low oxalate diet is recommended, avoiding foods such as spinach, rhubarb, beetroot, nuts, chocolate, tea, wheat bran, and strawberries 1
• Maintain adequate calcium intake (1,000-1,200 mg daily) primarily from food sources, timed with meals to bind oxalate in the gut 1, 3
• Reduce dietary fat intake and consider replacing with medium chain triglycerides 1, 2
• Increase fluid intake to achieve urine volume of at least 2.5 liters daily 1, 3
• Limit sodium intake to 2,300 mg daily 1, 3

Pharmacological Approaches

• Oral cholestyramine administration may help by binding bile acids, though evidence is mixed 1
• For patients with hypocitraturia, potassium citrate therapy may be beneficial 1, 3
• Thiazide diuretics can be considered for patients with hypercalciuria 1

Special Considerations

Enteric Hyperoxaluria

• Patients with malabsorptive conditions (inflammatory bowel disease, Roux-en-Y gastric bypass) may require more restrictive oxalate diets 1
• Higher calcium intake, including supplements specifically timed with meals, may be needed to enhance gastrointestinal binding of oxalate 1

Monitoring

• 24-hour urine specimen should be obtained within six months of initiating treatment to assess response 3
• Regular monitoring of stone burden through imaging is recommended 3

Prevention of Recurrence

• Maintaining adequate hydration is crucial to prevent recurrent stone formation 1, 3
• Dietary modifications should be continued long-term to manage both diarrhea and prevent stone recurrence 1, 2