What is the most likely diagnosis for a patient with lung cancer, severe neutropenia, and symptoms of diffuse abdominal pain and diarrhea following chemotherapy?

Typhlitis (Neutropenic Enterocolitis)

The most likely diagnosis is typhlitis (neutropenic enterocolitis), which is the most common cause of acute abdominal pain in neutropenic cancer patients, typically occurring 1-2 weeks after chemotherapy initiation. 1, 2

Clinical Reasoning

This patient presents with the classic triad of neutropenic enterocolitis:

• Severe neutropenia (WBC 300/mm³) following chemotherapy for lung cancer 1
• Fever and diffuse abdominal pain with localization to the right lower quadrant 1, 3
• Diarrhea as part of the gastrointestinal symptom complex 1, 4

The timing is characteristic—symptoms appearing during the nadir of chemotherapy-induced bone marrow suppression, typically 1-2 weeks post-chemotherapy. 1, 2 The physical examination findings of diffuse tenderness with mild guarding in the right lower quadrant are consistent with ileocecal involvement, the hallmark anatomic distribution of typhlitis. 1

Why Not the Other Diagnoses

Diverticulitis typically affects older patients and involves the left colon (sigmoid), not the right lower quadrant, and would be unusual without prior antibiotic exposure or other predisposing factors. 1

Ischemic colitis generally affects watershed areas (splenic flexure, rectosigmoid junction) and presents in patients with vascular risk factors or hypotension, neither of which are described here. 1

Giardiasis is a parasitic infection causing watery diarrhea without the acute inflammatory picture, fever, or localized right lower quadrant findings seen in this patient. 1

Diagnostic Confirmation

Imaging is mandatory and should not be delayed:

• Contrast-enhanced CT scan is the gold standard, showing bowel wall thickening >4 mm (transversal) or >30 mm (longitudinal) in the cecum and terminal ileum 1
• Ultrasound can demonstrate bowel wall thickening >5 mm, with mortality risk dramatically increasing when thickness exceeds 10 mm (60% vs 4.2%) 1, 2
• Look for complications: pneumatosis intestinalis, free air (perforation), ascites, or fluid-filled bowel loops 1

Laboratory workup must include:

• Blood cultures (gram-negative Enterobacteriaceae are most common) 1
• Stool cultures and C. difficile toxin testing to exclude concurrent infection 1
• Complete metabolic panel and coagulation studies 1

Critical Management Points

Conservative management is the cornerstone unless complications develop: 1

• Bowel rest with nasogastric suction 5
• Broad-spectrum antibiotics immediately: piperacillin/tazobactam OR a carbapenem (imipenem/cilastatin, meropenem, or doripenem) with anti-pseudomonal activity 1
• Hydration and total parenteral nutrition 5
• Consider G-CSF to accelerate neutrophil recovery 1, 5
• Avoid antiperistaltic agents and laxatives—these are contraindicated 1, 5

Surgical consultation should be obtained early, but intervention is reserved for: 1

• Bowel perforation (free air on imaging)
• Intestinal obstruction
• Massive hemorrhage
• Abscess formation
• Progressive clinical deterioration despite maximal medical therapy

Mortality Considerations

This is a life-threatening condition with mortality rates reaching 29.5% in patients with positive radiologic findings. 1, 2 The mortality risk is directly correlated with bowel wall thickness on imaging, emphasizing the critical importance of early CT scanning. 1 Patients who develop complications requiring surgery have significantly higher mortality, making aggressive medical management and close monitoring essential. 5, 4

The absence of prior antibiotic prophylaxis in this severely neutropenic patient (WBC 300/mm³) represents a missed opportunity for risk reduction, though this does not change the current management approach. 1