Colitis (Infectious / Ischemic / Inflammatory)
Inflammatory disease of the colon — etiology drives management
Symptoms / Associated Sx
Diarrhea (watery, bloody, or mucoid), crampy lower abdominal pain
Fever (infectious, IBD; less common in ischemic)
Rectal urgency and tenesmus (distal colitis/proctitis)
Hematochezia (ischemic, severe IBD, invasive infectious)
Denies
Recent antibiotics (reduces C. diff if truly absent)
Recent travel, sick contacts, shellfish (rules out travel-related infectious colitis)
Known IBD (rules out IBD flare if absent — first presentation can occur)
Vascular disease, hypotension, recent aortic surgery (rules out ischemic if absent)
Social History (SHx)
Recent antibiotics (C. diff), travel history (Salmonella, Campylobacter, Shigella, STEC), immunosuppression (CMV colitis), prior IBD, vascular disease (ischemic colitis), radiation history.
Main Etiology
Infectious: C. diff, Salmonella, Shigella, Campylobacter, STEC O157:H7, Yersinia, CMV (immunocompromised), Entamoeba
Ischemic: Low-flow, atherosclerosis, cocaine, vasopressors; watershed zones
Inflammatory (IBD): UC (continuous, rectum to proximal); Crohn's (skip lesions, transmural)
Microscopic colitis: NSAIDs, PPIs, SSRIs; normal colonoscopy; watery non-bloody diarrhea
Most Common DDx
C. difficile colitis (recent antibiotics; watery non-bloody diarrhea initially; WBC >15k; C. diff PCR positive; pseudomembranes on colonoscopy)
IBD flare (known IBD or first presentation; fecal calprotectin very elevated; colonoscopy shows characteristic distribution — continuous UC vs. skip lesions Crohn's)
Ischemic colitis (elderly + vascular risk factors + low-flow state; bloody diarrhea at watershed zones; CT shows wall thickening; colonoscopy shows mucosal ischemia)
STEC / E. coli O157:H7 (bloody diarrhea + no fever initially; undercooked beef/spinach exposure; do NOT give antibiotics; check CBC/Cr for HUS)
Microscopic colitis (watery non-bloody diarrhea + normal colonoscopy macroscopically; biopsy diagnostic; middle-aged women; NSAID/PPI/SSRI use)
Diverticulitis (LLQ pain + fever; CT shows pericolic stranding; no diarrhea as dominant symptom; stool not bloody unless complicated)
Colorectal cancer with colitis-like presentation (weight loss + change in bowel habits; colonoscopy and biopsy)
DATA
CBC, CMP, CRP, ESR; fecal calprotectin; stool cultures (Salmonella, Shigella, Campylobacter, STEC); C. diff PCR; stool O&P; CMV PCR
CT abdomen/pelvis; KUB (toxic megacolon); colonoscopy or sigmoidoscopy (pattern, biopsy)
Lactate; BUN:Cr (dehydration)
Home Meds
NSAIDs (hold — worsen colitis); antidiarrheals/loperamide (hold — toxic megacolon risk)
Antibiotics (may have precipitated C. diff); immunosuppressants (IBD — continue vs. hold per infection concern)
Plan
IV fluids, electrolyte replacement; NPO if severe; advance diet as tolerated in mild-moderate
Infectious:
Most viral/mild bacterial → supportive; AVOID antibiotics + antidiarrheals in STEC
Salmonella (severe/bacteremic): Ciprofloxacin 500 mg PO/IV BID × 5–7 days
Shigella: Azithromycin 500 mg daily × 3 days or Ciprofloxacin 500 mg BID × 3 days
Campylobacter (severe): Azithromycin 500 mg daily × 3 days
Entamoeba: Metronidazole 500–750 mg TID × 7–10 days + Paromomycin 500 mg TID × 7 days
Ischemic colitis: Bowel rest + IVF; treat underlying low-flow state; Pip-tazo if fever/infection; surgery if peritonitis or no improvement
IBD flare: See IBD flare section below
Avoid loperamide in all active colitis; monitor for toxic megacolon (KUB if worsening; >6 cm = toxic megacolon → surgery)
Daily CBC, CMP, CRP; trend fever curve; follow cultures; GI + surgery consult; PT/OT
Discharge: Complete antibiotic course; hydration + BRAT diet advancing to regular; avoid NSAIDs; GI follow-up 2–4 weeks
Red Flags
Toxic megacolon (colon >6 cm + systemic toxicity) → NPO, NG tube, IV steroids/cyclosporine (IBD), surgery
Peritoneal signs → perforation → emergent surgery
STEC O157:H7 + HUS signs (microangiopathic hemolytic anemia + thrombocytopenia + AKI) → supportive only; no antibiotics
CMV colitis in steroid-refractory IBD → biopsy + tissue PCR; ganciclovir before escalating IBD therapy
Senior IM Resident Pearls
Ischemic colitis classic locations: Splenic flexure and rectosigmoid (watershed areas); right colon ischemia = more severe
STEC antibiotics increase HUS risk ~10× — most important antibiotic contraindication in GI medicine
Microscopic colitis: Budesonide 9 mg PO daily × 8 weeks — most effective; stop offending drugs (NSAIDs, PPIs, SSRIs) first
Common mistake: Loperamide in IBD flare or infectious colitis — risk of toxic megacolon
ORDERS
Labs
Admission Labs
CBC with diff
CMP
BMP
CRP
ESR
Lactate
Magnesium
Phosphorus
Stool Studies
C. difficile PCR
GI pathogen panel / stool culture
Stool culture for Salmonella, Shigella, Campylobacter
STEC/Shiga toxin testing
Stool O&P
Fecal leukocytes
Fecal calprotectin
Stool occult blood
Additional Labs
CMV PCR (immunocompromised)
HIV test if immunocompromised
Blood cultures ×2 (fever/sepsis)
Iron studies if chronic bloody diarrhea
Trending Labs
CBC daily
CMP daily
CRP daily
Lactate q4–6 hr if ischemic/septic
Monitor Cr closely (HUS risk)
Imaging
First-Line
CT Abdomen/Pelvis with Contrast
Evaluate:
Colitis distribution
Ischemia
Perforation
Abscess
Toxic megacolon
If Toxic Megacolon Concern
KUB Daily
Evaluate:
Colon diameter
Free air
Toxic megacolon:
Colon >6 cm
Additional Imaging
CTA Abdomen/Pelvis
If:
Ischemic colitis
Mesenteric ischemia concern
Severe abdominal pain out of proportion
Procedures
Diagnostic
Colonoscopy / Flexible Sigmoidoscopy
IBD diagnosis
Ischemic colitis confirmation
Biopsy
CMV diagnosis
Avoid Full Colonoscopy
If:
Toxic megacolon
Severe fulminant colitis
Surgery
If:
Perforation
Toxic megacolon
Fulminant ischemic colitis
Necrosis
Medications
Supportive Care
IV Fluids
LR or NS
Aggressive electrolyte replacement
Diet
NPO if severe
Advance as tolerated
Infectious Colitis
C. difficile
Non-Severe/Severe
Vancomycin 125 mg PO QID x10 days
OR
Fidaxomicin 200 mg PO BID x10 days
Fulminant
Vancomycin 500 mg PO QID
PLUSMetronidazole 500 mg IV q8h
Salmonella (Severe/Bacteremic)
Ciprofloxacin
500 mg PO BID
OR400 mg IV q12h
x5–7 days
Shigella
Azithromycin
500 mg PO daily x3 days
OR
Ciprofloxacin
500 mg PO BID x3 days
Campylobacter
Azithromycin
500 mg PO daily x3 days
Entamoeba Histolytica
Metronidazole
500–750 mg PO TID x7–10 days
THEN
Paromomycin
500 mg PO TID x7 days
STEC (E. coli O157:H7)
Supportive Care Only
DO NOT GIVE:
Antibiotics
Loperamide
Monitor:
CBC
Platelets
Creatinine
(HUS surveillance)
Ischemic Colitis
Bowel Rest
NPO
IV Fluids
Aggressive hydration
Treat Underlying Cause
Hypotension
Shock
Vasoconstrictive drugs
Moderate-Severe Disease
Piperacillin-Tazobactam
4.5 g IV q6h
IBD Flare
Ulcerative Colitis
Methylprednisolone
60 mg IV daily
OR
20 mg IV q8h
Crohn's Disease
Methylprednisolone
40–60 mg IV daily
Severe/Refractory
GI-directed biologics
Microscopic Colitis
Budesonide
9 mg PO daily x8 weeks
Stop Offending Drugs
NSAIDs
PPIs
SSRIs
Hold Medications
Avoid
Loperamide
Diphenoxylate-atropine
Hold
NSAIDs
PPIs if causing microscopic colitis
Antibiotics if STEC suspected
Consults
Gastroenterology
All moderate/severe colitis
Colonoscopy
IBD
CMV concern
General Surgery
Toxic megacolon
Perforation
Fulminant ischemic colitis
Infectious Disease
CMV colitis
Severe infectious colitis
Refractory C. difficile
PT/OT
Deconditioning
Nutrition
Malnutrition
IBD
Prolonged NPO
Nursing Orders
Monitoring
Strict I&O
Stool count
Daily weights
Vital signs q4 hr
Diet
NPO if severe
Advance to low-residue diet
Notify Physician Immediately
Increasing abdominal distension
Peritoneal signs
Bloody diarrhea worsening
Fever
Hypotension
Follow-Up Studies
Daily
CBC
CMP
CRP
Follow
Stool cultures
C. difficile PCR
Calprotectin
Colonoscopy pathology
CMV testing
Escalation Criteria
Toxic Megacolon
Criteria:
Colon >6 cm
Systemic toxicity
Management:
NPO
NG tube
IV steroids (IBD)
Surgery consult STAT
Perforation
Signs:
Free air
Peritonitis
Rigid abdomen
→ Emergent surgery
STEC + HUS
Triad:
Hemolytic anemia
Thrombocytopenia
AKI
→ Supportive care
→ Nephrology consult
CMV Colitis
Ganciclovir
5 mg/kg IV q12h
Before escalating IBD immunosuppression