What is the differential diagnosis for a patient with intermittent lower left quadrant abdominal pain and lower back pain, normal white blood cell (WBC) count, no red blood cells (RBC), and trace proteinuria, and how should they be managed?

Differential Diagnosis and Management of Intermittent Left Lower Quadrant Pain with Lower Back Pain

Order CT abdomen and pelvis with IV contrast immediately—this is the gold standard imaging test with 98% diagnostic accuracy and will guide all subsequent management decisions. 1, 2

Most Likely Diagnoses

Your clinical presentation with intermittent left lower quadrant pain, lower back pain, normal WBC, and trace proteinuria most commonly represents:

• Acute diverticulitis (most common cause of left lower quadrant pain in adults), though the classic triad of left lower quadrant pain, fever, and leukocytosis is present in only 25% of cases 1, 2
• Urolithiasis (left-sided kidney stone), which can present with intermittent flank/back pain radiating to the lower quadrant, though the absence of RBCs on urinalysis makes this less likely 3, 4
• Colitis (inflammatory or infectious), which can cause intermittent pain without fever or leukocytosis in early stages 4
• Epiploic appendagitis (self-limited inflammation of colonic fat appendages), which presents with localized left lower quadrant pain without systemic symptoms 5, 4

Critical Imaging Decision

CT abdomen and pelvis with IV contrast is rated 8/9 (usually appropriate) by the American College of Radiology and should NOT be delayed. 1, 2 Here's why this matters:

• Clinical examination alone has misdiagnosis rates of 34-68% for left lower quadrant pain 1, 2
• CT changes the diagnosis in 49% of patients and alters management in 42% of cases 1, 6
• CT detects complications (abscess, perforation, fistula) that require immediate intervention versus outpatient management 1
• CT reduces unnecessary hospital admissions by >50% when uncomplicated diverticulitis is confirmed 1

Alternative Imaging Considerations

• Ultrasound is NOT recommended as the initial test for your presentation—it is operator-dependent, limited by bowel gas and obesity, and cannot adequately visualize the colon or retroperitoneum where pathology likely exists 1, 6
• Plain radiography has no role in your workup—it has limited diagnostic value and rarely changes management 1

Management Algorithm Based on CT Results

If CT Shows Uncomplicated Diverticulitis:

• Conservative management WITHOUT antibiotics if you are immunocompetent (no diabetes, no immunosuppressive medications, not elderly) 2
• Clear liquid diet advancement as tolerated with oral analgesics for pain control 2
• Antibiotics (Ertapenem 1g daily or Eravacycline 1mg/kg twice daily) for maximum 7 days ONLY if immunocompromised or elderly 2

If CT Shows Complicated Diverticulitis:

• Small abscess (<4 cm): Antibiotics alone for 7 days without drainage 2
• Large abscess (≥4 cm): Percutaneous drainage PLUS antibiotics for 4 days 2
• Perforation with peritonitis: Emergency surgical consultation required 2

If CT Shows Urolithiasis:

• Pain control and hydration for stones <5mm (90% pass spontaneously) 3
• Urology referral for stones >5mm or persistent symptoms 3

If CT is Completely Normal:

• Reassurance and consideration of functional bowel disorder 6
• Gastroenterology referral if symptoms persist 6

Red Flags Requiring Emergency Department Evaluation NOW

Go to the emergency department immediately if you develop any of these:

• Fever (temperature >100.4°F/38°C) combined with your pain 2
• Inability to pass gas or stool with abdominal distension 2
• Severe abdominal tenderness with guarding or rebound tenderness 2
• Vomiting that prevents oral intake 2
• Bloody stools 2
• Signs of shock (rapid heartbeat, confusion, dizziness) 2
• Progressively worsening pain over several days 2

Special Considerations for Your Urinalysis Findings

• Trace proteinuria alone is nonspecific and does not significantly narrow the differential diagnosis 3
• Absence of RBCs makes urolithiasis less likely but does not exclude it—10-15% of kidney stones present without hematuria 3
• Normal WBC does not exclude diverticulitis—leukocytosis is absent in many cases of uncomplicated diverticulitis 1, 2

Critical Pitfall to Avoid

Do NOT assume this is "just muscle strain" or "benign back pain" without imaging. The combination of left lower quadrant and back pain has a broad differential that includes life-threatening conditions like perforated viscus, abscess, or (rarely) ruptured abdominal aortic aneurysm in older patients. 2, 3 Clinical examination alone is unreliable, and imaging is essential to guide appropriate management. 1, 2

When Outpatient Management May Be Appropriate

You can potentially manage this outpatient ONLY if:

• Pain is mild and stable without fever or systemic symptoms 2
• You can tolerate oral intake and have normal bowel movements 2
• No signs of peritonitis on examination (no severe tenderness, guarding, or rebound) 2
• AND you obtain CT imaging within 24-48 hours to confirm the diagnosis 1, 2