A patient with a confirmed streptococcal infection on five days of penicillin remains febrile and CT shows circumferential small‑bowel wall thickening; what is the most likely etiology?

Persistent Fever with Small Bowel Thickening After Streptococcal Pharyngitis Treatment

The most likely cause is a concurrent intra-abdominal infectious or inflammatory process unrelated to the streptococcal pharyngitis, requiring immediate evaluation for complications such as enteritis, early Crohn's disease, or ischemic bowel, rather than treatment failure of the streptococcal infection itself.

Why This Is Not Streptococcal Treatment Failure

Group A streptococcus remains universally susceptible to penicillin with no documented resistance, making true microbiologic failure extremely unlikely 1. While clinical failure rates of penicillin for streptococcal pharyngitis have been reported at approximately 30%, these are primarily due to non-compliance, reexposure, or copathogenicity with other pharyngeal flora—not penicillin resistance 2. Importantly, streptococcal pharyngitis does not cause small bowel wall thickening on CT, making this an entirely separate pathologic process 3.

Immediate Diagnostic Priorities for Small Bowel Thickening

Assess for Life-Threatening Complications First

• Evaluate for perforation: Look for extraluminal gas, focal wall defects, or fluid/fat stranding along the bowel, which occurs in 89% of perforation cases 4
• Check for obstruction: Assess luminal narrowing from edema or inflammation that may require urgent surgical consultation 4
• Rule out active bleeding: Identify hyperdense blood products or contrast extravasation 4

Determine the Pattern of Bowel Wall Thickening

Segmental or diffuse thickening (>5 cm involvement) suggests benign inflammatory, infectious, or ischemic conditions rather than malignancy 3. The key CT features to analyze include:

• Symmetry: Circumferential symmetric thickening with fold enlargement suggests ischemic colitis, while asymmetric thickening with mesenteric fat stranding and engorged vasa recti points toward Crohn's disease 5
• Perienteric changes: Fat stranding disproportionately more severe than the degree of wall thickening strongly suggests an inflammatory condition 3
• Mural stratification: Thickened bowel showing layered enhancement with surrounding inflammatory changes is characteristic of Crohn's disease 6

Most Likely Differential Diagnoses

Infectious Enteritis

• Bacterial gastroenteritis (Salmonella, Campylobacter, Shigella) can cause segmental small bowel wall thickening with fever and systemic symptoms 6
• The patient may have developed a concurrent gastrointestinal infection unrelated to the pharyngitis
• Stool cultures and consideration of empiric antibiotics covering gram-negative bacteria and anaerobes may be warranted if peritoneal signs develop 6

Early Crohn's Disease

• Terminal ileum and right-sided small bowel involvement is the classic presentation of Crohn's disease 6, 5
• CT findings include asymmetric wall thickening, skip lesions, prominent mesenteric fat stranding, and engorged vasa recti 6, 5
• Endoscopic evaluation with biopsy showing transmural inflammation and granulomas would confirm the diagnosis 5

Ischemic Enteritis

• Circumferential symmetric wall thickening with fold enlargement on CT is characteristic 5
• Consider in patients with vascular risk factors or recent hypotensive episodes
• Histology would show ghost cells and hyalinized lamina propria if biopsied 5

Critical Next Steps

Immediate Clinical Assessment

• Monitor for peritoneal signs: Tenderness, rebound, guarding, along with fever, nausea, vomiting, and abdominal distension 6
• Obtain laboratory tests: WBC, CRP, procalcitonin, hemoglobin, and electrolytes to assess severity of inflammation 6
• Repeat CT if clinical deterioration occurs, especially if surgical intervention is being considered 6

Antibiotic Management

If peritoneal signs or systemic toxicity develop:

• Initiate broad-spectrum coverage for gram-negative bacteria and anaerobes (e.g., ceftriaxone 1-2 g IV daily + metronidazole 500 mg IV every 8 hours, or ciprofloxacin 400 mg IV every 12 hours + metronidazole) 7
• Continue for 3-5 days after adequate source control if an infectious process is confirmed 6, 7
• Do not extend antibiotics beyond 5 days without clear indication, as this increases resistance without improving outcomes 7

Definitive Diagnosis

• Upper endoscopy with biopsy is the reference standard if duodenal involvement is suspected 4
• Colonoscopy with ileoscopy and biopsy if terminal ileum or right colon involvement suggests Crohn's disease 5
• Tissue diagnosis will differentiate among Crohn's disease (granulomas), infectious colitis (pathogen-specific changes), and ischemic enteritis (ghost cells) 5

Common Pitfalls to Avoid

• Do not assume the streptococcal infection is resistant to penicillin—this is virtually impossible given universal susceptibility 1
• Do not attribute small bowel pathology to pharyngitis—these are anatomically and pathophysiologically unrelated processes
• Do not delay imaging or surgical consultation if peritoneal signs worsen, as complications like perforation or abscess require urgent intervention 6, 4
• Avoid empiric antibiotics for suspected inflammatory bowel disease once infection has been excluded, as they may worsen outcomes 5