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Approach to Abdominal Pain with Fever

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1. Pathophysiology of Pain (the "Why")

"The sensitivity of fever for acute appendicitis is only 67%" — normal temperature does not exclude serious pathology, especially in the elderly or immunocompromised. — Yamada's Textbook of Gastroenterology, 7th ed.

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2. History: The Most Powerful Diagnostic Tool

Pain characterization (SOCRATES)

• Onset: Sudden (perforation, ruptured ectopic, AAA, mesenteric ischemia) vs. gradual (appendicitis, cholecystitis, diverticulitis)
• Character: Colicky (obstruction, ureteric colic) vs. constant (peritonitis, ischemia)
• Location and radiation: Guides anatomical differential (see Section 4)
• Severity: Severe pain out of proportion to examination → mesenteric ischemia until proven otherwise
• Progression: Migrating from periumbilical → RIF = classic appendicitis

Fever characterization

• Timing relative to pain onset
• Rigors → bacteremia/sepsis (cholangitis, pyelonephritis, intra-abdominal abscess)
• High fever (>39°C) with jaundice + RUQ pain = Charcot's triad (cholangitis)

Associated symptoms

Key history elements

• Prior similar episodes: Diverticulitis, gallstone disease, pancreatitis, sigmoid volvulus
• Menstrual/sexual history: Ectopic pregnancy, PID (mandatory in women of reproductive age)
• Medications: NSAIDs (PUD, perforation), corticosteroids (mask peritonitis), antibiotics (C. difficile), anticoagulants (intramural hematoma)
• Alcohol/drugs: Pancreatitis, hepatitis, mesenteric ischemia (cocaine)
• Travel/food history: Typhoid, amoebic abscess, Anisakis

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3. Physical Examination

General inspection

• Lies still, rigid → peritonitis
• Writhes/restless → visceral or colic pain (early appendicitis, renal colic)
• Pale, diaphoretic, tachypneic → sepsis, hemorrhage, ischemia

Vital signs

Abdominal examination sequence: Inspect → Auscultate → Percuss → Palpate

• Distension → obstruction, ileus
• Cullen sign (periumbilical ecchymosis) / Grey-Turner sign (flank ecchymosis) → retroperitoneal hemorrhage (hemorrhagic pancreatitis, AAA)
• Surgical scars, hernias, skin rashes (herpes zoster)

• Absent bowel sounds → peritonitis or paralytic ileus
• High-pitched rushes synchronous with pain → mechanical small bowel obstruction

• Percussion tenderness is the most sensitive sign of peritonitis (preferred over rebound for patient comfort and specificity)
• Loss of hepatic dullness → free air (perforated viscus)

• Voluntary guarding: Conscious protective muscle contraction
• Involuntary guarding (rigidity): Reflex abdominal wall spasm = peritoneal irritation; most reliable sign of peritonitis
• Rebound tenderness (Blumberg's sign): Elicit by percussion rather than deep release to avoid unnecessary pain
• Rovsing's sign: RIF pain on palpating LIF → appendicitis
• Psoas sign: Extension of right hip causes pain → retrocecal appendicitis or psoas abscess
• Obturator sign: Internal rotation of flexed right hip → pelvic appendicitis or pelvic abscess
• Murphy's sign: Inspiratory arrest on deep palpation of RUQ → acute cholecystitis

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4. Differential Diagnosis by Location

RUQ

• Acute cholecystitis (most common cause of RUQ pain + fever)
• Acute cholangitis (Charcot's triad / Reynolds' pentad + shock + confusion)
• Hepatic abscess (pyogenic or amoebic)
• Acute hepatitis (viral, alcoholic)
• Subphrenic abscess
• Right lower lobe pneumonia/empyema

Epigastric

• Acute pancreatitis (epigastric → back, fever indicates necrosis/infection)
• Perforated peptic ulcer
• Acute gastritis

RLQ

• Acute appendicitis (most common cause requiring surgery)
• Mesenteric adenitis
• Crohn's disease (terminal ileitis)
• Meckel's diverticulitis
• Cecal diverticulitis
• Right-sided ovarian pathology (cyst, TOA, ectopic pregnancy)
• Psoas abscess

LLQ

• Acute diverticulitis (most common cause of LLQ pain + fever in older adults)
• Left-sided ovarian pathology
• Sigmoid volvulus

Hypogastric/Suprapubic

• Pelvic inflammatory disease (PID) / Tubo-ovarian abscess (TOA)
• Cystitis / pyelonephritis
• Ectopic pregnancy

Diffuse/Generalized

• Primary peritonitis (SBP in cirrhosis)
• Secondary peritonitis (perforated viscus, anastomotic leak)
• Acute mesenteric ischemia (pain out of proportion to exam)
• Typhoid fever (rose spots, relative bradycardia)
• Spontaneous bacterial peritonitis
• Strangulated bowel

Extra-abdominal causes (always consider)

• Right lower lobe pneumonia (referred diaphragmatic pain)
• Myocardial infarction (inferior wall)
• Diabetic ketoacidosis
• Addisonian crisis
• Herpes zoster (dermatomal pain before rash)

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5. Investigations

Bedside

• Urine dipstick/pregnancy test (mandatory in women of reproductive age → ectopic pregnancy)
• Blood glucose

Blood tests

Imaging

CT abdomen-pelvis with IV contrast is the investigation of choice when clinical diagnosis is uncertain, there is evidence of peritonitis, or sepsis is present.

Scoring systems

• Alvarado score (MANTRELS): Appendicitis
• Ranson/BISAP criteria: Pancreatitis severity
• Revised Atlanta classification: Pancreatitis
• Tokyo Guidelines: Cholecystitis and cholangitis severity

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6. Principles of Management

Immediate resuscitation (if unwell)

1. A-B-C-D: Airway, breathing, circulation
2. IV access × 2, IV fluids (crystalloid bolus if hypotensive)
3. O₂ supplementation
4. Continuous monitoring: HR, BP, SpO₂, urine output
5. IV analgesia — opioids are safe and do NOT mask peritonitis (evidence-based)

Antibiotics

• Start promptly in suspected sepsis or peritonitis — blood cultures first
• Cover gram-negative enteric organisms and anaerobes: piperacillin-tazobactam, or cefuroxime + metronidazole
• For cholangitis: add biliary-penetrating agents; consider early ERCP
• Tailor to culture results

Surgical consultation

• Perforated viscus
• Acute appendicitis (gangrenous/perforated)
• Strangulated hernia/bowel obstruction
• Ruptured ectopic pregnancy
• Mesenteric ischemia
• Ruptured AAA

• Acute appendicitis (uncomplicated)
• Acute cholecystitis (laparoscopic cholecystectomy within 72 hours)
• Diverticulitis with abscess or perforation
• TOA not responding to antibiotics

Specific management highlights

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7. Special Populations

Elderly

• Presentation is frequently atypical — fever may be absent or low-grade
• Higher prevalence of mesenteric ischemia, diverticulitis, AAA, malignancy
• Normal vital signs do not exclude serious pathology; have a lower threshold for CT

Immunocompromised (HIV, chemotherapy, steroids)

• Atypical pathogens: mycobacteria, CMV, fungi
• Peritonitis may occur without fever or guarding due to blunted response
• Corticosteroids can mask peritoneal signs entirely
• Neutropenic enterocolitis (typhlitis) in chemotherapy patients presenting with RLQ pain + fever

Pregnant women

• Appendix is displaced superiorly → atypical location of tenderness
• First-line imaging: ultrasound; MRI preferred if ultrasound inconclusive (avoid CT if possible)
• Ectopic pregnancy must be excluded in all first-trimester women with pain + fever

Children

• Mesenteric adenitis (viral) is a common benign mimic of appendicitis
• Intussusception (episodic colicky pain + bloody stool + mass)
• Meckel's diverticulitis

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8. "Red Flag" Features Requiring Immediate Action

• Hemodynamic instability (hypotension, tachycardia)
• Septic shock: lactate >2 + hypotension → follow Sepsis-6 bundle
• Peritonitis (involuntary guarding, absent bowel sounds, percussion tenderness)
• Pain out of proportion to examination → mesenteric ischemia
• Pulsatile abdominal mass → AAA
• Free air on CXR → perforated viscus
• Positive pregnancy test + abdominal pain + fever → ectopic pregnancy until proven otherwise

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