Irritable Bowel Syndrome vs Colorectal Cancer

Why Irritable bowel syndrome is correct

• This presentation is classic irritable bowel syndrome (IBS) per Rome IV criteria: recurrent abdominal pain at least 1 day/week for 3 months, associated with defecation, change in stool frequency or consistency.
• No alarm features are present (no nocturnal symptoms, weight loss, blood in stool, or elevated inflammatory markers).
• Normal colonoscopy rules out inflammatory bowel disease (IBD).

Why the others are wrong

• Bile acid malabsorption — causes painless or urgency-predominant watery diarrhea, typically after ileal resection, cholecystectomy, or Crohn disease, and does not produce the alternating constipation or the stress-triggered pain relieved by defecation described here.
• Celiac disease — Celiac serology is reasonable to check, but the overall presentation fits IBS.
• Functional dyspepsia — Functional dyspepsia is centered on upper GI symptoms (epigastric pain, early satiety), not the diffuse cramping and altered bowel habits described here.

Additional high-yield points

• First-line management includes reassurance, dietary modification (low-FODMAP diet), soluble fiber for constipation-predominant IBS, and antispasmodics for pain.

Why Neoadjuvant chemoradiotherapy is correct

• This is locally advanced (stage III, T3N1M0) rectal adenocarcinoma in the mid-rectum (6 cm from the anal verge).
• Standard of care is neoadjuvant (preoperative) therapy before total mesorectal excision.
• Neoadjuvant chemoradiotherapy reduces local recurrence from roughly 25% down to 5-8% and can downstage the tumor to permit sphincter preservation.
• Accepted regimens include long-course chemoradiation (5-FU or capecitabine with 45-54 Gy) or short-course radiotherapy.
• Total neoadjuvant therapy (delivering all chemotherapy and radiation before surgery) has improved complete-response rates in the RAPIDO and PRODIGE 23 trials.

Why the others are wrong

• A) Immediate low anterior resection — skips the downstaging step and yields higher local recurrence rates in node-positive disease; it is not the preferred first move for a T3N1 tumor.
• B) Transanal endoscopic microsurgery — a local-excision technique appropriate only for early, favorable T1 lesions; it does not address nodal disease and is inadequate for a T3N1 tumor.
• C) Systemic chemotherapy alone — FOLFOX (fluorouracil, leucovorin, oxaliplatin) is the backbone for metastatic colorectal disease and can be part of multimodal therapy, but as a standalone initial treatment it omits the radiation and surgery this localized tumor requires.