Is it normal for a patient with end-stage breast cancer (BCa) and liver and bone metastases (mets) with hepatomegaly and ascites, on nasogastric tube (NGT) feeding twice a day and receiving morphine (opioid analgesic) every 8 hours for pain, to experience frequent, dark brown, soft, and watery bowel movements?

Frequent Dark Brown Watery Stools in End-Stage Breast Cancer with Liver Metastases

This bowel pattern is abnormal and concerning in this clinical context—it likely represents paradoxical diarrhea from fecal impaction, hepatic dysfunction affecting bile metabolism, or morphine-induced bowel dysmotility rather than normal bowel function. 1

Primary Differential Considerations

Most Likely: Paradoxical Diarrhea from Opioid-Induced Impaction

• Morphine every 8 hours causes constipation in approximately 50% of advanced cancer patients and nearly all patients on chronic opioids 1
• Paradoxical diarrhea occurs when liquid stool bypasses a fecal impaction higher in the colon, presenting as frequent watery bowel movements 1
• The dark brown color suggests the stool has been in contact with colonic bacteria for an extended period, consistent with overflow around impaction 1
• Critical pitfall: Clinicians often mistake overflow diarrhea for normal bowel function and fail to perform digital rectal examination 2

Hepatic Dysfunction Contributing to Stool Changes

• With hepatomegaly and liver metastases, impaired bile metabolism can alter stool color and consistency 1
• Hepatic dysfunction affects fluid and electrolyte balance, potentially contributing to loose stools 1
• Ascites indicates advanced hepatic compromise, which can affect intestinal motility and absorption 1

Opioid-Induced Bowel Dysmotility

• Morphine acts on μ-opioid receptors in the gastrointestinal tract, causing increased non-propulsive contractions, increased fluid absorption, and altered transit time 1
• This can paradoxically present as either constipation or altered bowel patterns including loose stools 1

Immediate Assessment Required

Perform digital rectal examination immediately to rule out fecal impaction 1, 2

• Impaction must be excluded before any treatment escalation 1, 2
• If impaction is present, manual disimpaction or glycerin suppositories are indicated 1

Assess for bowel obstruction 1, 2

• With hepatomegaly and peritoneal disease (ascites), mechanical obstruction from tumor compression is possible 1
• Plain abdominal X-ray should be obtained if there is abdominal distension, pain, or concern for obstruction 2

Evaluate metabolic derangements 1

• Check calcium (hypercalcemia from bone metastases causes constipation) 1
• Check potassium (hypokalemia worsens bowel dysmotility) 1
• Assess hydration status given limited NGT feeding 1

Management Algorithm

If Impaction is Present:

1. Manual disimpaction or glycerin suppositories 1
2. After disimpaction, initiate prophylactic bowel regimen with stimulant laxative (senna or bisacodyl 10-15 mg 2-3 times daily) 1
3. Add osmotic laxative (polyethylene glycol) if stimulant alone is insufficient 1
4. Goal: one non-forced bowel movement every 1-2 days 1

If No Impaction but Opioid-Induced Constipation Suspected:

1. Initiate stimulant laxative prophylactically—this should have been started when morphine was initiated 1
2. Docusate (stool softener) alone is NOT recommended and has not shown benefit 2
3. If laxatives fail, consider peripherally-acting μ-opioid receptor antagonist (methylnaltrexone 0.15 mg/kg subcutaneously) 1, 2

If Hepatic Dysfunction is Primary:

• Address underlying metabolic issues (hydration, electrolytes) 1
• Optimize nutrition through NGT if tolerated 1
• Consider increasing NGT feeding frequency beyond twice daily if patient can tolerate 1

Critical Pitfalls to Avoid

Never assume frequent loose stools mean the bowel is functioning normally in an opioid-treated patient 1

• Overflow diarrhea from impaction is extremely common and frequently missed 1

Do not use bulk laxatives (psyllium) in this population 2

• Bulk laxatives are contraindicated in opioid-induced constipation and can worsen obstruction 2

Opioid-induced constipation should have been anticipated and treated prophylactically when morphine was started 1

• All patients on opioids should receive concurrent stimulant laxatives unless contraindicated by pre-existing diarrhea 1

Check for other constipating medications 1

• Antiemetics (especially 5-HT3 antagonists like ondansetron), anticholinergics, and antacids all worsen constipation 1, 2
• Consider alternative antiemetics if ondansetron is being used 2

Additional Considerations

Limited NGT feeding (only twice daily) may contribute to bowel dysfunction 1

• Inadequate fluid and nutrition intake worsens constipation 1
• Consider increasing feeding frequency if patient tolerates 1

In end-stage disease with ascites and hepatomegaly, bowel obstruction from tumor must remain on the differential 1

• If obstruction is present, treatment shifts to symptom management rather than aggressive bowel regimen 1