What is the differential diagnosis for a 23-year-old female with epigastric abdominal pain migrating to the right lower quadrant (RLQ), vomiting, leukocytosis, and no fever or urinary/vaginal symptoms, with a negative pregnancy test?

Acute Appendicitis: Immediate Diagnostic Workup Required

This is acute appendicitis until proven otherwise—proceed immediately with contrast-enhanced CT abdomen/pelvis with IV contrast, which is the definitive diagnostic test with 85.7-100% sensitivity and 94.8-100% specificity. 1, 2

Pelvic Exam Decision

Do NOT perform a pelvic exam in this patient. 1, 3 The clinical presentation strongly suggests appendicitis (migratory epigastric pain to RLQ with vomiting and leukocytosis), and she has no urinary or vaginal symptoms that would indicate gynecologic pathology. 2, 4 A pelvic exam would delay definitive imaging without adding diagnostic value in this scenario. 1

Differential Diagnosis (In Order of Likelihood)

Most Likely: Acute Appendicitis

• Classic presentation: Epigastric pain migrating to RLQ is pathognomonic for appendicitis, with leukocytosis and vomiting supporting this diagnosis. 2, 4
• The absence of fever does NOT exclude appendicitis—afebrile presentation occurs in a significant proportion of cases, particularly early in the disease course. 5
• Vomiting typically follows pain onset in appendicitis, which fits this presentation. 4

Alternative Gynecologic Diagnoses (Less Likely Given Negative Symptoms)

• Ovarian torsion: Possible but less likely without acute onset severe pain and typically presents with more dramatic symptoms. 1, 3
• Ruptured ovarian cyst: Can cause RLQ pain but usually has sudden onset and may have associated vaginal bleeding. 1, 3
• Pelvic inflammatory disease (PID): Unlikely given absence of vaginal symptoms, though 15% of untreated chlamydia leads to PID. 3
• Tubo-ovarian abscess: Would typically present with fever and vaginal discharge. 1

Gastrointestinal Causes

• Mesenteric adenitis: Can mimic appendicitis but less common in this age group. 2
• Infectious enterocolitis: Possible given vomiting, but RLQ localization and leukocytosis favor appendicitis. 2
• Perforated jejunal diverticulum: Rare in young patients (mean age 68 years) and presents with more diffuse peritonitis. 6

Urologic Causes

• Ureterolithiasis: Less likely without urinary symptoms, but should be on differential. 1, 3
• Pyelonephritis: Unlikely without fever, dysuria, or flank pain. 3

Immediate Diagnostic Algorithm

Step 1: Laboratory Testing

• Complete blood count (CBC): Already shows leukocytosis, supporting appendicitis. 4
• C-reactive protein (CRP): Significantly elevated in appendicitis; normal inflammatory markers have 100% negative predictive value for excluding appendicitis. 2, 4
• Basic metabolic panel: Assess for dehydration from vomiting and electrolyte abnormalities. 2
• Urinalysis: Essential to exclude urinary tract infection or urolithiasis. 5
• Pregnancy test confirmation: Already negative, but document this clearly. 1

Step 2: Physical Examination Specifics

• Test for psoas sign: Pain with hip extension or flexion suggests appendicitis or retroperitoneal pathology. 2, 4
• Assess for rebound tenderness and guarding at McBurney's point. 4
• Rovsing's sign: Pain in RLQ with palpation of left lower quadrant. 4

Step 3: Imaging

• CT abdomen/pelvis with IV contrast (WITHOUT oral contrast): This is the gold standard with 90-100% sensitivity and 94.8-100% specificity. 1, 2
• Do NOT delay for oral contrast administration—this increases time to diagnosis and potentially increases perforation risk without improving diagnostic accuracy. 2, 4
• Ultrasound is NOT appropriate as initial imaging in this age group with classic appendicitis presentation—it has only 18% sensitivity compared to CT's >90%. 1

Management Based on CT Results

If Appendicitis Confirmed:

• Proceed directly to appendectomy as standard treatment. 4
• Initiate broad-spectrum antibiotics immediately. 5
• If perforated with abscess >3cm: Consider percutaneous drainage followed by delayed appendectomy. 2, 4

If CT Negative but High Clinical Suspicion:

• Diagnostic laparoscopy has both diagnostic and therapeutic value. 4

Critical Pitfalls to Avoid

• Do NOT rely on absence of fever to exclude appendicitis—this is a common error that delays diagnosis. 5
• Do NOT use clinical scoring systems (Alvarado score) alone—they may not accurately exclude appendicitis with atypical presentations. 2, 5
• Do NOT delay imaging for additional clinical observation—pregnant women with perforated appendicitis have higher fetal loss rates, emphasizing need for early diagnosis even in non-pregnant patients. 1
• Do NOT order MRI as initial imaging in non-pregnant patients—CT is faster, more available, and equally accurate. 1

Symptomatic Management While Awaiting Imaging

• IV fluid resuscitation for dehydration from vomiting. 4
• Antiemetics: Dopamine antagonists (metoclopramide or prochlorperazine) or serotonin antagonists for nausea control. 4
• Keep patient NPO in anticipation of potential surgery. 4