What is the differential diagnosis and initial work‑up for a 36‑year‑old man with left‑upper‑quadrant pleuritic abdominal pain?

Left Upper Quadrant Pleuritic Abdominal Pain in a 36-Year-Old Man

Order CT abdomen and pelvis with IV contrast immediately—this is the mandatory first-line imaging study for left upper quadrant pain, rated 8/9 (usually appropriate) by the American College of Radiology, with near-perfect diagnostic accuracy and the ability to detect life-threatening conditions that clinical examination alone will miss in 34–68% of cases. 1, 2

Differential Diagnosis

The pleuritic quality of the pain (sharp, worse with breathing or movement) significantly narrows your differential and raises concern for diaphragmatic irritation or processes involving the pleura, peritoneum, or capsular organs:

High-Priority Life-Threatening Causes

• Splenic pathology (infarction, rupture, abscess)—the spleen's capsular stretch causes pleuritic pain that may radiate to the left shoulder (Kehr sign). 1
• Perforated viscus (gastric perforation, splenic flexure perforation)—free intraperitoneal air on CT has 92% positive predictive value and mandates immediate surgical consultation. 3, 1
• Acute pancreatitis—confirm with serum lipase >2× upper limit of normal; mortality is <10% overall but reaches 30% in severe disease. 1
• Midgut volvulus with ischemia—rare in adults but can present with sudden-onset upper quadrant pain; CT may reveal malrotation with atypical appendiceal location. 1, 4

Common Non-Emergent Causes

• Splenic flexure diverticulitis or colitis—CT provides high diagnostic accuracy for colonic pathology extending into the left upper quadrant. 1
• Pyelonephritis or nephrolithiasis—renal pathology should be excluded in cases without fever; CT with IV contrast will identify perinephric fat stranding, hydronephrosis, or calculi. 1, 2
• Musculoskeletal/abdominal wall pain—consider if pain is reproducible with palpation or movement, though imaging is still warranted given the pleuritic nature. 2

Rare but Critical Diagnoses

• Subphrenic abscess—fever with pleuritic pain suggests intra-abdominal abscess; CT is the gold standard. 1
• Pulmonary embolism with diaphragmatic irritation—though primarily a chest diagnosis, lower lobe PE can present as upper abdominal pain. (general medical knowledge)

Initial Work-Up Algorithm

Immediate Actions (Before Imaging)

1. Assess hemodynamic stability—hypotension, tachycardia, or signs of shock require immediate IV access, fluid resuscitation, and surgical consultation. 3

2. Obtain focused laboratory tests:

   • Complete blood count (leukocytosis suggests infection/inflammation) 2
   • Serum lipase (>2× upper limit confirms pancreatitis) 1
   • C-reactive protein (CRP >50 mg/L increases likelihood of inflammatory process; CRP >170 mg/L predicts severe disease with 87.5% sensitivity) 3, 1
   • Hepatobiliary markers (AST, ALT, bilirubin, alkaline phosphatase) 2
   • Urinalysis (to exclude urinary tract pathology) 2

3. Check for peritoneal signs:

   • Rebound tenderness, guarding, or rigidity indicates peritonitis and mandates immediate CT followed by surgical evaluation. 3, 1
   • Absent bowel sounds suggest perforation or advanced peritonitis. 3

Imaging Strategy

CT abdomen and pelvis with IV contrast is non-negotiable—do not rely on plain radiographs (very limited diagnostic value) or ultrasound (limited by overlying bowel gas and rib shadowing in the left upper quadrant). 1, 2, 5

• Why CT with IV contrast?

  • Provides comprehensive evaluation of splenic, pancreatic, gastric, colonic, renal, and vascular pathology in a single study. 1
  • Detects free intraperitoneal air (perforation), free fluid (peritonitis), and abscess formation. 3, 1
  • Alters diagnosis in nearly 50% of cases with nonlocalized abdominal pain. 1
  • Reduces hospital admissions by >50% through accurate risk stratification. 1

• Alternative imaging only if:

  • Pregnant patient—use ultrasound first, then MRI if ultrasound is nondiagnostic. 2
  • Severe contrast allergy or renal failure—consider non-contrast CT, though diagnostic accuracy is reduced. 3

Management Based on CT Findings

If CT Shows Perforation (Free Air)

• Immediate surgical consultation for exploratory laparotomy. 3, 1
• Start broad-spectrum antibiotics after blood cultures. 3
• NPO status, IV fluid resuscitation, nasogastric decompression. 1

If CT Shows Splenic Pathology

• Splenic infarction/rupture—surgical consultation; hemodynamically unstable patients require emergent splenectomy. 1
• Splenic abscess—percutaneous drainage vs. splenectomy depending on size and patient stability. 1

If CT Shows Pancreatitis

• Supportive care: IV fluids (aggressive early resuscitation), pain control, antiemetics, NPO initially. 1
• Monitor for complications (necrosis, pseudocyst, hemorrhage). 1

If CT Shows Diverticulitis/Colitis

• Uncomplicated disease: outpatient management without antibiotics if immunocompetent. 3
• Complicated disease (abscess, perforation): antibiotics ± percutaneous drainage ± surgery. 3

If CT Shows Renal Pathology

• Pyelonephritis: antibiotics based on local resistance patterns. 1
• Nephrolithiasis: pain control, hydration, urology referral if obstructing stone. 1

Critical Pitfalls to Avoid

• Do not assume benign etiology based on age—midgut volvulus, though rare in adults, can present with sudden-onset upper quadrant pain and requires emergent surgery. 4, 6
• Do not delay imaging for laboratory results—CT should be ordered immediately in patients with pleuritic pain and any concerning features (fever, peritoneal signs, hemodynamic instability). 1, 2
• Do not use plain radiographs as the primary imaging modality—they have very limited diagnostic value and delay definitive diagnosis. 1, 7
• Do not miss referred pain from lower lobe pneumonia or pulmonary embolism—if CT abdomen is negative, consider chest imaging. 2

When to Escalate Care

• Immediate surgical consultation if: peritoneal signs, free air on CT, hemodynamic instability, or suspected volvulus/ischemia. 3, 1, 4
• ICU admission if: septic shock, severe pancreatitis, or multi-organ dysfunction. 3, 1