A 35-year-old woman from Bangalore presents with a 2-year history of intermittent diarrhea, right lower quadrant pain, and weight loss. Colonoscopy reveals skip lesions with cobblestone appearance and aphthous ulcers in the terminal ileum. Biopsy shows transmural inflammation with non-caseating granulomas. She has erythema nodosum on the shins. Laboratory studies show elevated inflammatory markers and normal albumin. She has not received any immunosuppressive therapy. What is the most appropriate next step in management?

Explanation

## Clinical Scenario Analysis This patient has **Crohn disease (CD)** with the following classic features: - Skip lesions (discontinuous inflammation) - Cobblestone appearance and aphthous ulcers - **Transmural inflammation with non-caseating granulomas** (pathognomonic for CD) - Terminal ileal involvement (most common site in CD) - Extraintestinal manifestation: erythema nodosum - First presentation, steroid-naive, normal albumin (not severely malnourished) ## Why CT Enterography Is the Critical Next Step **Key Point:** Before initiating systemic therapy in CD, **imaging of the entire small bowel is essential** to: 1. Define the full extent of disease (CD is patchy; skip lesions may extend beyond colonoscopic reach) 2. Detect complications: fistulas, strictures, abscesses, perforation 3. Guide therapeutic strategy (medical vs. surgical) 4. Establish baseline for monitoring **High-Yield:** CT enterography is superior to colonoscopy alone because it visualizes the entire small bowel (colonoscopy reaches only to terminal ileum) and assesses transmural disease, mesenteric inflammation, and complications. ## Management Algorithm for CD Induction ```mermaid flowchart TD A[Confirmed CD diagnosis]:::outcome --> B[CT enterography]:::action B --> C{Complications present?}:::decision C -->|Fistula/abscess| D[Percutaneous drainage + antibiotics]:::action C -->|Stricture/obstruction| E[Consider surgery]:::action C -->|None| F{Disease severity?}:::decision F -->|Mild-moderate, no complications| G[Corticosteroids or 5-ASA]:::action F -->|Moderate-severe| H[Corticosteroids + azathioprine/biologics]:::action G --> I[Assess response at 4 weeks]:::decision H --> J[Assess response at 4 weeks]:::decision ``` ## Induction Therapy Hierarchy for CD | Disease Severity | First-Line Therapy | Rationale | |---|---|---| | Mild-moderate, no complications | Corticosteroids (prednisolone 40–60 mg/day tapering) OR 5-ASA | Rapid anti-inflammatory effect | | Moderate-severe | Corticosteroids + azathioprine/6-MP (start early) | Steroid-sparing; immunomodulation | | Severe/fulminant | IV methylprednisolone + infliximab (if no contraindications) | Rapid response; TNF inhibition | | Fistulizing CD | Infliximab ± azathioprine; percutaneous drainage if abscess | TNF inhibitors are DOC for fistulas | **Clinical Pearl:** Infliximab is NOT first-line for induction of remission in uncomplicated CD; it is reserved for: - Moderate-to-severe disease refractory to corticosteroids - Fistulizing disease - Steroid-dependent disease **Mnemonic:** **STEP-UP** — **S**mall bowel imaging first, **T**hen assess complications, **E**scalate therapy based on severity, **P**redict need for surgery, **U**se biologics for refractory/fistulizing disease, **P**erform monitoring. ## Why Corticosteroids Alone Is Premature While corticosteroids will be part of the induction regimen, **imaging must precede systemic therapy** to exclude complications that would change management (e.g., an abscess would require drainage before or alongside antibiotics and steroids; a stricture might warrant surgery).