Clues Pointing TO This Diagnosis

Left lower/left-sided abdominal pain — left-sided (sigmoid) pain is the most common presenting symptom of acute diverticulitis
Gradual onset progressing over days to a week — about 70% of patients present with gradual-onset left lower quadrant pain
Fever — fever occurs in roughly one-third of patients and signals significant inflammation
Poor oral intake/inability to eat — anorexia and nausea are common associated symptoms
Localized left-sided tenderness on exam — left lower quadrant tenderness with localized guarding is the typical finding
Leukocytosis ("white count off the chart") — an elevated WBC count and CRP are typical of diverticulitis
Age 61 with long-standing low-fiber, processed diet — older age and low dietary fiber intake are established risk factors
CT showing an inflamed diverticulum with surrounding fat stranding/fluid — contrast CT confirming pericolic inflammation is diagnostic
CT showing no perforation or abscess — absence of abscess, perforation, fistula, or obstruction defines uncomplicated disease
Underlying diverticulosis ("pouches in the wall") — diverticulitis is inflammation of pre-existing colonic diverticula

Why It's NOT the Similar Diseases

NOT acute appendicitis — appendicitis classically causes right lower quadrant pain (McBurney point); Vincent's pain is left-sided, the hallmark of sigmoid diverticulitis
NOT colorectal cancer — cancer typically produces chronic symptoms such as weight loss, change in stool caliber, and iron-deficiency anemia rather than an acute febrile inflammatory episode, though it can mimic diverticulitis and warrants later colonoscopy
NOT irritable bowel syndrome — IBS causes chronic pain with altered bowel habits but no fever, leukocytosis, or CT inflammation
NOT inflammatory bowel disease — IBD causes chronic diarrhea, often bloody, with systemic features over time; Vincent has an acute localized episode with focal CT inflammation
NOT nephrolithiasis — a ureteral stone causes colicky flank-to-groin pain with hematuria, not localized left lower quadrant tenderness with fever and leukocytosis

Differential Diagnosis List

Acute appendicitis — ruled out by left-sided rather than right lower quadrant localization
Colorectal cancer — ruled out acutely by CT showing diverticular inflammation, but excluded definitively by follow-up colonoscopy
Irritable bowel syndrome — ruled out by fever, leukocytosis, and CT inflammatory changes
Inflammatory bowel disease — ruled out by acute localized presentation with focal diverticular inflammation on CT
Nephrolithiasis — ruled out by absence of colicky flank pain and hematuria; CT shows colonic not urinary pathology

Key Distinguishing Test

Contrast-enhanced CT of the abdomen and pelvis is the recommended confirmatory test, with a sensitivity of roughly 94%–99% and specificity of about 99%.
Findings of localized bowel-wall thickening with pericolic fat stranding confirm uncomplicated diverticulitis, while an abscess, extraluminal air/contrast, fistula, or obstruction indicates complicated disease.
A purely clinical diagnosis is correct in only about 40%–65% of cases, which is why imaging is generally obtained.

Board Note

Diverticulitis is left-sided (sigmoid) in most Western patients; classic presentation is left lower quadrant pain, low-grade fever, nausea/anorexia, and leukocytosis, and rectal bleeding is not typical of acute diverticulitis
For uncomplicated diverticulitis, current guidelines support observation with supportive care (pain control with acetaminophen, hydration, diet modification) and selective—not routine—antibiotics; antibiotics are reserved for systemic symptoms, immunocompromise, significant comorbidities, or age >80
When antibiotics are indicated for outpatient uncomplicated disease, first-line oral options are amoxicillin/clavulanate or a cephalosporin (e.g., cefalexin) plus metronidazole to cover gram-negatives and anaerobes
Complications include abscess (most common), perforation, obstruction, stricture, and fistula; an abscess above a size threshold is treated with percutaneous drainage, and free perforation with peritonitis requires emergent surgery
Colonoscopy is contraindicated during the acute episode; it is performed 6–8 weeks after resolution to exclude colorectal cancer after a first episode of uncomplicated disease or after complicated disease
Long-term prevention emphasizes a high-fiber diet rich in fruits, vegetables, and whole grains with reduced red meat; elective surgery is individualized (impact on quality of life) and is no longer dictated by episode count

“Vincent’s Story”