What is the appropriate management approach for constipation in a 42‑year‑old woman with hypothyroidism and hypertension?

Management of Constipation in a 42-Year-Old Woman with Hypothyroidism and Hypertension

Start by optimizing her hypothyroidism treatment first, as this is a reversible cause of constipation, then implement a stepwise bowel regimen beginning with polyethylene glycol (PEG) 17g daily as first-line pharmacological therapy. 1, 2

Step 1: Address the Underlying Hypothyroidism

• Check thyroid-stimulating hormone (TSH) levels immediately to confirm adequate thyroid hormone replacement, as hypothyroidism directly causes constipation through decreased colonic motility and slowed intestinal transit 1, 3, 4
• Target TSH should be 0.5-2.0 mIU/L for optimal symptom control in a 42-year-old woman 3
• If TSH is elevated, adjust levothyroxine dosing before pursuing aggressive constipation treatments, as correcting hypothyroidism may resolve constipation entirely 1, 3, 5
• Recheck TSH 6-8 weeks after any dose adjustment 4, 6

Step 2: Review and Modify Medications

• Conduct a complete medication review to identify constipating agents, particularly focusing on her antihypertensive regimen 1, 2
• Calcium channel blockers (commonly used for hypertension) are notorious for causing constipation 1
• If she is on calcium channel blockers, consider switching to alternative antihypertensives that do not worsen constipation, such as ACE inhibitors or thiazide-like diuretics 1
• Discontinue any non-essential constipating medications as the first intervention 2, 7

Step 3: Perform Focused Physical Examination

• Conduct a careful digital rectal examination that specifically assesses for fecal impaction, rectal masses, and pelvic floor motion during simulated evacuation (ask her to "bear down" and "expel my finger") 1, 2
• Check for a rectocele or pelvic floor dysfunction, though a normal exam does not exclude defecatory disorders 1
• Look for abdominal masses or distension that might suggest obstruction 1

Step 4: Limited Laboratory Testing

• Only obtain a complete blood count unless other clinical features warrant additional testing 1
• Do NOT routinely check calcium, glucose, or additional metabolic panels in the absence of other symptoms, as their diagnostic yield is extremely low and not cost-effective 1
• Her TSH should already be checked as part of Step 1 1, 3

Step 5: Implement Non-Pharmacological Measures

• Increase fluid intake to at least 1.5 liters daily, which is essential for all subsequent interventions to work 2, 7
• Establish a regular toileting routine: attempt defecation 30 minutes after meals (especially breakfast) when the gastrocolic reflex is strongest, limiting straining to no more than 5 minutes 2, 7
• Increase physical activity within her capabilities 2, 7
• Gradually increase dietary fiber intake ONLY if she maintains adequate fluid intake and physical activity; otherwise fiber can worsen constipation 1, 7

Step 6: First-Line Pharmacological Treatment

• Start polyethylene glycol (PEG) 17g mixed with 8 oz of water once daily as the first-line laxative due to superior efficacy and excellent safety profile 2, 7
• PEG is specifically recommended by the American Gastroenterological Association as first-line therapy 2
• PEG can be titrated up to twice daily if needed 7
• Goal is one non-forced bowel movement every 1-2 days 1, 2

Step 7: Add Second-Line Agents if PEG Alone is Insufficient

• Add bisacodyl 10-15 mg daily (stimulant laxative) if PEG alone does not achieve adequate bowel movements within 1-2 weeks 1
• Alternative osmotic agents include lactulose 30-60 mL twice daily or magnesium hydroxide 30-60 mL daily 1
• Senna (2-3 tablets twice daily) is another effective stimulant option 1, 7

Step 8: Rectal Interventions for Severe Cases

• If digital rectal exam reveals impaction, perform manual disimpaction with premedication using analgesics ± anxiolytics 1, 2
• Follow with glycerin suppository or bisacodyl suppository (one rectally daily) 1
• Mineral oil retention enema or tap water enema can be used for severe impaction 1

Common Pitfalls to Avoid

• Do not rely on docusate (stool softener) alone, as it is ineffective for both prevention and treatment of constipation 7
• Do not increase fiber without ensuring adequate fluid intake, as this will worsen constipation 7
• Do not perform colonoscopy unless she has alarm features (blood in stool, anemia, weight loss) or is due for age-appropriate colon cancer screening 1
• Do not order extensive metabolic testing (calcium, glucose) without specific clinical indications, as the yield is extremely low 1

When to Refer or Escalate

• If constipation persists despite optimized thyroid replacement and maximal medical therapy, consider anorectal manometry and colonic transit studies to evaluate for defecatory disorders or slow transit constipation 1
• Refer to gastroenterology if there is concern for structural obstruction or if symptoms persist after 8-12 weeks of appropriate treatment 1