What is the diagnostic approach for an elderly patient with chronic diarrhea and a palpable mass in the left lower quadrant?

Diagnostic Approach for Elderly Patient with Chronic Diarrhea and Palpable Left Lower Quadrant Mass

This elderly patient requires urgent colonoscopy with biopsies as the diagnostic procedure of choice, given the combination of chronic diarrhea and a palpable abdominal mass, which raises immediate concern for colorectal malignancy. 1, 2

Why Colonoscopy is Mandatory in This Case

The presence of a palpable mass in the left lower quadrant represents an alarm feature that mandates urgent gastroenterology referral and full colonoscopy. 2, 3 The British Society of Gastroenterology specifically emphasizes that patients over 45 years with chronic diarrhea require full colonoscopy due to the frequency and clinical significance of colonic neoplasia in older subjects. 1, 2

Key Clinical Reasoning

• Colorectal cancer accounts for 60% of large bowel obstructions in elderly patients, and the combination of chronic diarrhea with a palpable mass is highly suspicious for malignancy. 4

• A palpable left lower quadrant mass with chronic diarrhea could represent:

  • Colorectal carcinoma (most concerning) 4
  • Complicated diverticular disease with phlegmon or abscess 4
  • Inflammatory bowel disease with stricture or mass effect 1
  • Sigmoid volvulus (though typically presents more acutely) 4

• Elderly patients have significantly higher rates of complicated presentations requiring surgery (22%) and mortality (up to 8%) compared to younger patients, making prompt diagnosis critical. 4

Immediate Diagnostic Workup Before Colonoscopy

While arranging urgent colonoscopy, obtain:

• Contrast-enhanced CT scan of abdomen and pelvis to characterize the mass, assess for obstruction, perforation, or metastatic disease, and guide surgical planning if needed. 4

• Laboratory investigations including complete blood count (to assess for anemia from chronic blood loss), C-reactive protein, comprehensive metabolic panel, liver function tests, iron studies, vitamin B12, folate, and anti-tissue transglutaminase IgA with total IgA. 2, 5

• Fecal calprotectin to assess for inflammatory bowel disease if not immediately proceeding to colonoscopy. 2

• Stool culture and C. difficile toxin to exclude infectious causes, though less likely given chronicity. 2, 5

• Digital rectal examination is mandatory to detect rectal mass, fecal impaction, or blood. 4

Critical Colonoscopy Protocol

When performing colonoscopy, biopsies must be obtained from both right and left colon even if mucosa appears normal, as microscopic colitis has entirely normal-appearing mucosa endoscopically but shows characteristic histologic changes. 2 This is particularly important because microscopic colitis is a common cause of chronic diarrhea in elderly patients. 1, 6

Common Pitfalls to Avoid

• Do not rely on CT imaging alone to exclude significant colonic pathology, as CT is inadequate for detecting microscopic colitis, early inflammatory bowel disease, or subtle mucosal abnormalities visible only endoscopically with histology. 2

• Do not assume functional diarrhea (IBS) in an elderly patient with a palpable mass—this represents an alarm feature requiring structural evaluation. 2, 3

• Do not delay colonoscopy for empiric treatment trials when alarm features are present, as this delays diagnosis of potentially life-threatening conditions. 1, 3

• Only 50% of elderly patients with acute left colonic diverticulitis present with lower quadrant pain, and typical signs may be masked, leading to delayed diagnosis. 4

If Colonoscopy is Negative

If colonoscopy with biopsies is unrevealing:

• Consider upper endoscopy with duodenal biopsies if celiac serology is positive or small bowel malabsorption is suspected. 2

• Test for bile acid diarrhea with SeHCAT or serum 7α-hydroxy-4-cholesten-3-one if colonoscopy is negative. 2

• Small bowel imaging with CT or MR enterography if inflammatory bowel disease affecting the small bowel is suspected. 1