Differential Diagnosis for Nausea, Vomiting, Back Pain, and Right Lower Quadrant Pain
The most critical diagnosis to exclude is acute appendicitis, which classically presents with periumbilical pain migrating to the right lower quadrant, accompanied by nausea and vomiting. 1, 2
Primary Differential Diagnoses
Acute Appendicitis (Most Critical)
- Classic presentation includes periumbilical or epigastric pain migrating to the right lower quadrant, nausea, vomiting, and anorexia. 3, 4, 2
- Fever is present in only approximately 50% of cases, so its absence does not exclude appendicitis. 1
- Vomiting occurring after pain onset increases likelihood of appendicitis, whereas vomiting before pain makes appendicitis less likely. 3
- Back pain may represent atypical appendicitis with retrocecal appendix location. 4
Gynecologic Pathology (in Women of Reproductive Age)
- Ovarian torsion, ruptured ovarian cyst, tubo-ovarian abscess, or ectopic pregnancy must be considered in women with irregular menses. 5
- Urine pregnancy test is mandatory before imaging to exclude ectopic pregnancy. 5
- Pelvic inflammatory disease can present with similar symptoms. 5
Urologic Conditions
- Nephrolithiasis with ureteral stones can cause right lower quadrant pain radiating to the back. 5
- Urinalysis is essential to exclude urinary tract infection or stone disease. 5
Gastrointestinal Conditions
- Right colonic diverticulitis occurs in 8% of patients presenting with right lower quadrant pain. 1
- Intestinal obstruction accounts for 3% of cases. 1
- Infectious colitis, including typhlitis in immunocompromised patients. 6
Other Considerations
- Ischemic colitis in patients with vascular risk factors. 6
- Blunt abdominal trauma history (if present) can cause traumatic appendicitis. 7
Diagnostic Approach Algorithm
Step 1: Initial Clinical Assessment
- Assess for peritoneal signs (guarding, rigidity, rebound tenderness), fever, and migration of pain to right lower quadrant. 3, 1
- Positive psoas sign or McBurney sign significantly increases likelihood of appendicitis. 3, 1
- Check vital signs for hypotension, tachycardia, or signs of sepsis. 3
Step 2: Laboratory Evaluation
- Complete blood count to assess for leukocytosis (supports appendicitis but has limited diagnostic power with positive likelihood ratio of only 2.47). 1, 5
- Urinalysis to exclude urinary tract infection or nephrolithiasis. 5
- Urine pregnancy test in all women of reproductive age. 5
- Serum lactate if sepsis is suspected. 3
Step 3: Imaging Strategy
- CT abdomen and pelvis with IV contrast is the definitive imaging study for adults and adolescents with right lower quadrant pain, achieving 85.7-100% sensitivity and 94.8-100% specificity for appendicitis. 3, 1, 5
- CT identifies alternative diagnoses in 23-45% of patients with right lower quadrant pain. 1, 5
- Ultrasound may be considered as initial imaging in children or pregnant patients to avoid radiation, followed by CT if inconclusive. 1, 8
- MRI is appropriate for pregnant patients when ultrasound is inconclusive, with 96% sensitivity and specificity. 3, 1
Step 4: Risk Stratification
- High-risk features requiring urgent intervention include peritoneal signs, fever, leukocytosis, and imaging showing appendiceal diameter >8.2 mm with periappendiceal fat stranding. 1, 2
- Low-risk patients without fever, with normal appetite, and benign examination may be discharged with mandatory 24-hour follow-up. 1
Critical Pitfalls to Avoid
- Never rely on absence of fever to exclude appendicitis—it is absent in 50% of cases. 1
- Do not discharge patients without establishing clear 24-hour follow-up and return precautions for worsening symptoms. 1
- Avoid delaying imaging if symptoms persist or worsen during observation period. 1
- NSAIDs can mask evolving symptoms and delay diagnosis—use cautiously. 1
- In immunocompromised patients (HIV/AIDS), consider typhlitis and other opportunistic infections in the differential. 6