Ulcerative Colitis in a Patient with Hashimoto's Thyroiditis
Most Likely Diagnosis
In a patient with Hashimoto's thyroiditis presenting with acute bloody diarrhea and elevated CRP with normal ESR, ulcerative colitis is the most likely diagnosis, given the known association between these autoimmune conditions and the characteristic inflammatory pattern. 1, 2
The discordance between elevated CRP and normal ESR is particularly informative in this clinical scenario. CRP rises rapidly (within 12-24 hours) as a direct acute-phase reactant in response to IL-6, making it highly sensitive to acute colonic inflammation, whereas ESR reflects chronic inflammation and may remain normal early in disease presentation. 3 In ulcerative colitis specifically, CRP has 63% sensitivity and 77% specificity for detecting moderate-to-severe endoscopic inflammation, and this marker correlates more closely with disease activity than ESR in approximately two-thirds of pediatric UC patients. 3, 4
The coexistence of Hashimoto's thyroiditis and ulcerative colitis has been documented in multiple case reports, suggesting a common autoimmune pathophysiologic background. 1, 2 Patients with one autoimmune disorder are at increased risk for developing additional autoimmune conditions, and gastrointestinal symptoms in this population warrant thorough investigation for inflammatory bowel disease. 2
Immediate Diagnostic Steps
Initial Laboratory Assessment
- Complete blood count to assess for anemia, which is common in UC and may also affect ESR interpretation 5
- Comprehensive metabolic panel including electrolytes (hyponatremia can occur with both conditions), renal function, and liver function tests 5, 1
- Stool studies for infectious diarrhea including Clostridium difficile toxin—this is mandatory before initiating immunosuppressive therapy 5
- Additional stool cultures for bacterial pathogens, as infection must be confidently excluded 6
Endoscopic Evaluation
Flexible sigmoidoscopy should be performed urgently rather than full colonoscopy if the patient meets criteria for moderate-to-severe disease, as colonoscopy carries higher perforation risk in acute severe colitis. 5
- Perform rigid or flexible sigmoidoscopy with rectal mucosal biopsies even if macroscopic appearance is normal 5, 6
- Look for characteristic UC features: loss of vascular pattern, granularity, friability, and ulceration of rectal mucosa 5
- Obtain multiple biopsies for histologic confirmation showing typical UC patterns (diffuse, continuous inflammation) and to exclude other diagnoses 5
Defer full colonoscopy until clinical condition improves if the patient has moderate-to-severe disease, as the perforation risk is unacceptably high in this setting. 5
Radiographic Assessment
- Plain abdominal radiograph is essential to exclude colonic dilatation (toxic megacolon) and assess disease extent 5, 6
- This should be repeated on alternate days during hospitalization if severe disease is present 6
Disease Severity Assessment
Determine if this patient meets criteria for severe UC using the Truelove and Witts criteria, as this dictates whether hospitalization is mandatory. 5
Severe UC is defined by:
- Bloody stool frequency ≥6 per day, PLUS
- Any ONE of the following:
- Tachycardia >90/min
- Temperature >37.8°C
- Hemoglobin <10.5 g/dL
- ESR >30 mm/h (or CRP >30 mg/L as substitute) 5
Important caveat: Even if criteria for severe disease are not met, admission is mandatory for any patient in their first attack of ulcerative colitis who presents with bloody diarrhea. 6 This patient with Hashimoto's thyroiditis presenting with new-onset bloody diarrhea requires hospitalization regardless of severity classification.
Therapeutic Approach
For Mild-to-Moderate Disease (Outpatient Management)
If the patient does not meet severe criteria and this is confirmed mild disease after endoscopy:
- Topical mesalamine 1g suppository once daily is first-line for proctitis 5
- Oral mesalamine combined with topical therapy is more effective than either alone 5
- Avoid topical steroids alone, as topical mesalamine is superior 5
For Severe Disease (Inpatient Management)
If the patient meets criteria for severe UC, immediate hospitalization with intensive monitoring and intravenous corticosteroids is required. 6
Immediate Treatment Protocol:
- Intravenous hydrocortisone 100mg four times daily (or equivalent corticosteroid) should be started as soon as diagnosis is made 6
- Monitor closely with:
- Plain abdominal X-ray on alternate days
- Full blood count, serum albumin, and CRP on alternate days
- Temperature and pulse rate four times daily 6
Antibiotics Consideration:
- Include antibiotics if infection cannot be confidently excluded, particularly while awaiting stool culture results 6
Nutritional Support:
- Free diet is allowed, but monitor nutritional status closely 6
- Provide intravenous fluid and electrolyte replacement if needed 6
Surgical Indications:
- Any evidence of colonic dilatation despite maximal medical therapy is an absolute indication for colectomy 6
- Cyclosporin therapy should be reserved for patients with poor response after 3-4 days of corticosteroid therapy, particularly those with CRP >45 mg/L who do not yet have absolute surgical indications 6
- Most patients who have not convincingly responded within 10 days should undergo colectomy, though partial responders who are afebrile may continue up to 14 days 6
Critical Monitoring Parameters
During Acute Phase:
- CRP should be measured every 2-4 days during active treatment, as it normalizes more rapidly than ESR and better reflects treatment response 3, 4
- ESR may remain elevated even after CRP normalizes during recovery, so do not rely solely on ESR for treatment decisions 3
- In approximately 34% of patients with mild UC and 5-10% with moderate-severe disease, both CRP and ESR may be completely normal despite active disease 4
Long-term Monitoring:
- Once remission is achieved, measure inflammatory markers every 3-6 months 7
- Endoscopic evaluation at 6-12 months after treatment initiation once symptoms and biomarkers normalize 7
Common Pitfalls and Caveats
Diagnostic Pitfalls:
- Do not assume lymphocytic colitis based solely on the Hashimoto's association—while 40% of Hashimoto's patients may have increased intraepithelial lymphocytes, most are asymptomatic, and acute bloody diarrhea with elevated CRP strongly suggests UC rather than lymphocytic colitis 8
- Normal ESR does not exclude significant disease activity in UC, particularly in acute presentations where CRP rises first 3, 4
- Anemia and azotemia artificially elevate ESR but do not affect CRP, so CRP is more reliable in this clinical context 7, 3
Treatment Pitfalls:
- Never delay stool cultures to start immunosuppression—infection must be excluded first 5, 6
- Do not perform colonoscopy in severe disease—flexible sigmoidoscopy is safer and sufficient for diagnosis 5
- Do not continue medical therapy beyond 10-14 days without clear improvement, as this increases mortality risk without reducing colectomy rates 6
- Inform the patient early about natural history and possible need for surgery—approximately 30-40% of patients with severe colitis require colectomy within 6 months 6
Monitoring Pitfalls:
- In approximately one-third of UC patients, CRP and ESR may be discordant (one elevated while the other is normal), so if one marker performs well for a given patient, continue using that marker preferentially 4
- CRP correlates more closely with endoscopic appearance than ESR (correlation 0.55 vs 0.41), making it the preferred marker for monitoring 4