What is the best initial management for a 58-year-old woman with severe constipation, normal colonoscopy and Double Contrast Barium (Ba) Enema results, and borderline thyroid-stimulating hormone (TSH) level?

Management of Severe Constipation with Borderline TSH Level

The most appropriate next step for this 58-year-old woman with severe constipation and borderline TSH level is to repeat thyroid function tests (option C), as subclinical hypothyroidism may be contributing to her constipation symptoms.

Clinical Assessment

This patient presents with:

• Severe constipation
• Colicky central abdominal pain
• Loss of appetite and malaise
• Prolonged total colon transit time (140 hours)
• Normal Double Contrast Ba Enema and colonoscopy
• Borderline TSH level (6.5 mU/L, with normal range 0.4-6.5 mU/L)
• Normal T3 and T4 levels

Rationale for Repeating Thyroid Function Tests

1. Borderline TSH with Potential Hypothyroidism:

   • The patient's TSH is at the upper limit of normal (6.5 mU/L, with normal range 0.4-6.5 mU/L)
   • Even subclinical hypothyroidism can cause constipation and should be ruled out before pursuing more invasive testing 1
   • Thyroid dysfunction is a recognized secondary cause of constipation that should be addressed before pursuing specialized testing 2

2. Exclusion of Secondary Causes First:

   • The American Gastroenterological Association recommends excluding secondary causes of constipation before pursuing specialized testing 2
   • Hypothyroidism is a treatable cause of constipation that should be identified early in the diagnostic process 1

3. Normal Structural Evaluation:

   • The patient has already had normal colonoscopy and barium enema, ruling out structural causes
   • This makes metabolic causes more likely to be contributing to symptoms

Why Other Options Are Less Appropriate

1. Anorectal manometry (Option A):

   • While useful for diagnosing defecatory disorders, this should be pursued only after excluding secondary causes like hypothyroidism 2
   • The AGA recommends anorectal testing only after excluding treatable medical conditions 2

2. Increase fibers and fluids (Option B):

   • While this is a first-line treatment for primary constipation, it would be premature without addressing potential thyroid dysfunction 2, 1
   • Lifestyle modifications alone are unlikely to resolve constipation if an underlying thyroid disorder exists

3. Investigate secret self-medications (Option D):

   • While medication use can cause constipation, there is no clinical evidence suggesting medication misuse in this case
   • The borderline TSH provides a more likely explanation that should be investigated first

Management Algorithm

1. Repeat thyroid function tests to confirm or rule out hypothyroidism

   • If confirmed hypothyroidism: Initiate thyroid replacement therapy
   • If normal thyroid function: Proceed to step 2

2. Review and adjust medications that may cause constipation

   • Consider calcium channel blockers, opioids, anticholinergics 1

3. Initiate conservative management:

   • Increase dietary fiber (20-25g daily) 1
   • Ensure adequate hydration (at least 8 glasses of water daily) 1
   • Encourage physical activity 1
   • Trial of osmotic laxatives (polyethylene glycol 17g daily) 2, 1

4. If no improvement after 2-4 weeks:

   • Proceed to specialized testing:
     • Colonic transit study (already done in this case)
     • Anorectal manometry to assess for defecatory disorders 2
     • Balloon expulsion test 3

5. Treatment based on findings:

   • For slow transit constipation: Stimulant laxatives or intestinal secretagogues 3
   • For defecatory disorders: Biofeedback therapy 2
   • For combined disorders: Combination therapy 2

Key Considerations

• Constipation with prolonged transit time (140 hours) is significant and warrants thorough investigation
• The borderline TSH value could represent early or subclinical hypothyroidism, which is a treatable cause of constipation
• A systematic approach starting with the least invasive and most potentially beneficial intervention (repeating thyroid tests) is most appropriate
• Specialized testing like anorectal manometry should be reserved for when treatable causes have been excluded