What is the appropriate workup and treatment for a patient with new onset constipation and diarrhea?

Workup for New Onset Constipation and Diarrhea

For a patient presenting with new onset constipation AND diarrhea together, the priority is to rule out fecal impaction with overflow diarrhea, followed by structural evaluation if alarm features are present, and infectious workup for the diarrhea component. 1

Initial Clinical Assessment

History and Physical Examination

Perform a careful digital rectal examination that includes assessment of pelvic floor motion during simulated evacuation to identify fecal impaction, which commonly presents as constipation with paradoxical diarrhea (overflow around impaction). 1 The examination should evaluate:

• Resting sphincter tone and squeeze effort 1
• Perineal descent during simulated defecation 1
• Presence of hard stool in the rectal vault (indicating impaction) 1
• Anal reflex and perianal skin for fecal soiling 1

Alarm Features Requiring Urgent Evaluation

Obtain colonoscopy or structural imaging if the patient has:

• Age >50 years without prior colorectal cancer screening 1
• Blood in stools or anemia 1
• Unintentional weight loss 1
• Abrupt onset of symptoms 1
• Fever with abdominal tenderness (concern for perforation or infection) 1

Laboratory Workup

Essential Tests

Complete blood count is the only mandatory test in the absence of other symptoms. 1

Conditional Tests

Metabolic testing (TSH, glucose, calcium, creatinine) is NOT routinely recommended unless clinical features suggest specific secondary causes (e.g., symptoms of hypothyroidism, diabetes). 1 The diagnostic utility and cost-effectiveness of routine metabolic panels are low. 1

Stool Studies for Diarrhea Component

Obtain stool workup including:

• Infectious studies (bacterial culture, C. difficile toxin, ova and parasites) 1
• Fecal lactoferrin to assess for inflammatory diarrhea 1

Diagnostic Imaging

Plain Abdominal Radiograph

Order if fecal impaction or obstruction is suspected to assess:

• Extent of fecal loading 1
• Bowel gas pattern to rule out mechanical obstruction 1

Structural Evaluation

Colonoscopy should NOT be performed in patients without alarm features unless age-appropriate screening has not been done. 1 However, if alarm features are present or impaction is ruled out and symptoms persist, proceed with colonoscopy or CT colonography to exclude:

• Mechanical obstruction 1
• Colorectal cancer 1
• Inflammatory bowel disease 1

Management Based on Findings

If Fecal Impaction is Present

This is the most common cause of combined constipation and diarrhea (overflow). 1

1. Administer glycerin suppository ± mineral oil retention enema 1
2. Perform manual disimpaction following premedication with analgesic ± anxiolytic 1
3. After disimpaction, initiate maintenance laxative therapy with bisacodyl 10-15 mg daily with goal of one non-forced bowel movement every 1-2 days 1

If No Impaction Found

Treat constipation and diarrhea components separately:

For Constipation:

• Discontinue constipating medications if feasible 1
• Trial of fiber supplementation (if adequate fluid intake) and/or over-the-counter laxatives 1
• Add bisacodyl or polyethylene glycol if initial measures fail 1

For Diarrhea:

• Hydration and electrolyte replacement 1
• Loperamide 4 mg initial dose, then 2 mg every 4 hours or after each unformed stool (maximum 16 mg/day) 1, 2
  • Caution: Avoid in patients with fever, bloody stools, or suspected C. difficile infection due to risk of toxic megacolon 2
• If infectious etiology identified, treat with appropriate antibiotics 1

If Symptoms Persist After 48 Hours

Reassess for:

• Recurrent impaction 1
• Mechanical obstruction (repeat imaging) 1
• Medication side effects 1
• Consider specialized testing: colonic transit study, anorectal manometry, or defecography if defecatory disorder suspected 1

Common Pitfalls

Do not assume alternating constipation and diarrhea is irritable bowel syndrome without first ruling out fecal impaction and structural disease. 1 A normal digital rectal examination does not exclude defecatory disorders or impaction higher in the colon. 1

Avoid loperamide in patients with bloody diarrhea, high fever, or severe abdominal pain as this may precipitate toxic megacolon, particularly in infectious or inflammatory colitis. 2

Do not perform extensive metabolic testing routinely as the yield is extremely low and not cost-effective. 1