What is the possible diagnosis and next steps for a 37-year-old male with a 3-day history of intermittent abdominal pain in the upper and lower quadrants of the left side, associated with normal-looking stool and an urge to defecate, who experienced temporary relief with Loperamide (Loperamide) and worsening pain after meals?

Differential Diagnosis and Next Steps for 37-Year-Old Male with Left-Sided Abdominal Pain

Most Likely Diagnosis

This presentation is most consistent with irritable bowel syndrome (IBS) or a functional gastrointestinal disorder, though diverticulitis and inflammatory bowel disease must be excluded given the left-sided location and pain progression. 1

Key Diagnostic Considerations

Clinical Features Pointing Away from Acute Diverticulitis

• The absence of fever and leukocytosis makes acute diverticulitis less likely, as the classic triad includes left lower-quadrant pain, fever, and leukocytosis 1
• The patient is 37 years old, and diverticulosis occurs in only 5-10% of persons by age 45 1
• The unremarkable physical examination without peritoneal signs argues against complicated diverticulitis 1

Red Flags Assessment

• No alarm features are present: no documented weight loss, no rectal bleeding, no anemia, no nocturnal symptoms, no family history of colon cancer, and no recent antibiotic use 1
• The normal-looking stool character without blood or discharge is reassuring 2
• Age under 50 without alarm features reduces concern for colorectal malignancy 3

Immediate Next Steps

Laboratory Evaluation Required

• Complete blood count to assess for anemia and inflammatory markers 4
• C-reactive protein or erythrocyte sedimentation rate to identify inflammatory processes 4
• Serum chemistries and albumin to assess for metabolic derangements 4
• Stool studies including fecal occult blood testing and fecal calprotectin to distinguish inflammatory from non-inflammatory causes 4, 3
• Celiac serology (IgA tissue transglutaminase with total IgA) given the chronic nature of symptoms 4, 3
• Thyroid-stimulating hormone to exclude hyperthyroidism as a cause of altered bowel habits 3

Imaging Decision Algorithm

CT imaging should be obtained if diagnostic uncertainty remains after initial laboratory evaluation, particularly given the pain progression to 7/10 after meals. 1

• The American College of Physicians recommends abdominal CT imaging when diagnostic uncertainty exists in suspected acute left-sided colonic diverticulitis 1
• CT abdomen and pelvis with oral and intravenous contrast is the most appropriate initial imaging study for left-sided abdominal pain with diagnostic uncertainty 1, 4
• CT has very high sensitivity and specificity for diagnosing diverticulitis and can identify alternative diagnoses 1
• If the patient has predictors of complicated disease or worsening symptoms, err on the side of imaging 1

When Imaging May Not Be Necessary

• Imaging may not be necessary if the patient has mild symptoms, normal laboratory values, and no alarm features, particularly if a functional disorder is suspected 1
• However, given the pain escalation to 7/10 after meals, imaging is warranted to exclude organic pathology 1

Alternative Diagnoses to Consider

Irritable Bowel Syndrome

• The postprandial pain exacerbation (within 90 minutes of eating) is characteristic of IBS, occurring in 50% of occasions in IBS patients 1
• The intermittent nature with urge to defecate and relief after bowel movements supports this diagnosis 1
• However, IBS is a diagnosis of exclusion requiring absence of alarm symptoms 2

Small Intestinal Bacterial Overgrowth (SIBO)

• SIBO can cause postprandial abdominal pain and altered bowel habits 1
• Consider if symptoms persist despite negative initial workup 1

Inflammatory Bowel Disease

• Left-sided colonic involvement can present with left lower quadrant pain 2
• Elevated inflammatory markers or positive fecal calprotectin would support this diagnosis 4

Management Algorithm

If Initial Workup is Negative

• Consider functional disorders and use loperamide for symptom control 4
• Loperamide is effective for painless diarrhea and alternating bowel habits with pain in IBS patients, improving stool frequency (36%), consistency (32%), and pain intensity (30%) 5, 6
• Dietary modifications should be implemented 4
• Tricyclic antidepressants can be used for abdominal pain and global symptoms 4

Critical Pitfall with Loperamide

• The patient has already taken loperamide with only temporary relief, suggesting either inadequate dosing or an underlying organic process requiring further investigation 7
• Loperamide should not be used when inhibition of peristalsis is to be avoided, and must be discontinued if constipation, abdominal distention, or ileus develop 7
• Avoid higher than recommended doses due to cardiac risks 7

If Organic Disease is Identified

• Treat the specific condition accordingly (e.g., antibiotics for diverticulitis, immunosuppression for inflammatory bowel disease) 4

Follow-up Strategy

• Re-evaluate in 3-6 weeks, and if symptoms worsen or new alarm features develop, repeat imaging and consider colonoscopy 4
• Colonoscopy with biopsies is indicated if age ≥50 years, presence of alarm features, or symptoms refractory to treatment 3
• Persistent symptoms despite treatment warrant referral to gastroenterology 4

Key Clinical Pearls

• The progression from 4-5/10 to 7/10 pain after meals is concerning and warrants investigation beyond symptomatic treatment 1
• The unremarkable physical examination does not exclude significant pathology, particularly early diverticulitis or inflammatory bowel disease 1
• Do not attribute symptoms to IBS without excluding organic disease first, especially given the pain escalation 2