What are the differential diagnoses for a patient presenting with leukocytosis (elevated white blood cell count) and lower right quadrant pain?

Differential Diagnoses for Elevated WBC and Right Lower Quadrant Pain

Appendicitis remains the primary diagnosis to exclude in any patient presenting with right lower quadrant pain and leukocytosis, and CT abdomen/pelvis with IV contrast should be obtained immediately to establish the diagnosis and identify alternative pathology. 1, 2

Primary Diagnostic Consideration

Acute Appendicitis

• Appendicitis is the most common surgical condition causing RLQ pain with leukocytosis, presenting classically in only 50% of cases with periumbilical pain migrating to the RLQ, fever, nausea, and elevated WBC. 2
• Elevated WBC with left shift has 80% sensitivity and 79% specificity for appendicitis when combined, with a positive likelihood ratio of 9.8. 3
• CT with IV contrast achieves 95% sensitivity and 94% specificity for appendicitis diagnosis and changes management in 43% of patients initially suspected clinically. 1, 2

Alternative Gastrointestinal Diagnoses

Inflammatory/Infectious Conditions of the Ileocecal Region

• Ileitis, colitis, and inflammatory bowel disease (particularly Crohn's disease with terminal ileal involvement) can present identically to appendicitis with RLQ pain and leukocytosis. 4, 5
• Infectious enterocolitis affecting the right colon mimics appendicitis clinically but is distinguished by CT findings. 5

Diverticulitis

• Cecal or ascending colon diverticulitis presents with RLQ pain and leukocytosis, identified in non-appendiceal diagnoses on CT in patients with suspected appendicitis. 4, 5
• Right-sided diverticulitis is less common than left-sided but clinically indistinguishable from appendicitis without imaging. 5

Appendiceal Diverticulitis

• Appendiceal diverticulitis carries higher perforation risk than routine appendicitis and may show intramural gas micro-loculations or saccular appendiceal contour on CT with asymmetric periappendiceal fat stranding. 6
• This entity is under-recognized but clinically significant due to possible neoplastic association requiring careful histopathologic assessment. 6

Bowel Obstruction and Perforation

• Small bowel obstruction or perforation presents with RLQ pain, leukocytosis, and can elevate amylase levels, creating diagnostic confusion. 4
• CT identifies these conditions with high accuracy and guides urgent surgical intervention. 4, 5

Mesenteric Ischemia

• Acute mesenteric ischemia affecting the right colon or terminal ileum presents with severe RLQ pain, leukocytosis, and elevated lactate. 4
• This represents a surgical emergency requiring immediate CT angiography for diagnosis. 4

Gynecologic Causes (in Reproductive-Age Females)

Ovarian and Adnexal Pathology

• Ovarian torsion, ruptured ovarian cyst, tubo-ovarian abscess, and pelvic inflammatory disease are the most frequent non-appendiceal diagnoses in females with RLQ pain. 1
• Ultrasound should be considered as initial imaging only when gynecologic pathology is the primary concern, though CT remains superior for comprehensive evaluation. 1

Ectopic Pregnancy

• Ruptured ectopic pregnancy must be excluded in any reproductive-age female with RLQ pain and leukocytosis, requiring pregnancy test and pelvic ultrasound. 1

Genitourinary Causes

Urologic Pathology

• Nephrolithiasis, pyelonephritis, and urinary tract infection can present with RLQ pain when involving the right kidney or ureter. 1
• Pyuria and hematuria on urinalysis help distinguish these from appendicitis, though CT provides definitive diagnosis. 1

Epiploic and Mesenteric Conditions

Epiploic Appendagitis

• Epiploic appendagitis results from torsion or inflammation of colonic epiploic appendages, presenting with localized RLQ pain and mild leukocytosis. 5
• CT shows characteristic oval fat-density lesion with surrounding inflammatory stranding adjacent to the colon. 5

Omental Infarction

• Primary omental infarction presents with acute RLQ pain mimicking appendicitis, identified on CT as heterogeneous fat-density mass with surrounding inflammatory changes. 5

Malignancies

Appendiceal and Cecal Neoplasms

• Appendiceal mucocele, cecal carcinoma, and lymphoma can present with RLQ pain and leukocytosis, particularly when complicated by perforation or obstruction. 5
• CT identifies mass lesions and guides appropriate oncologic workup. 5

Vascular and Musculoskeletal Causes

Vascular Pathology

• Iliopsoas hematoma or abscess presents with RLQ pain and leukocytosis, particularly in anticoagulated patients or those with bleeding disorders. 7

Musculoskeletal Conditions

• Rectus sheath hematoma and abdominal wall hernias can mimic intra-abdominal pathology but are distinguished by CT findings. 1

Critical Management Algorithm

Step 1: Obtain CT abdomen/pelvis with IV contrast immediately for any patient with RLQ pain and leukocytosis, as this provides 95% sensitivity and identifies the cause in the majority of cases. 1, 2

Step 2: If CT confirms appendicitis, proceed directly to surgical consultation regardless of WBC count, as normal WBC does not exclude appendicitis. 1, 2

Step 3: If CT shows alternative diagnosis, 41% of non-appendiceal diagnoses require hospitalization and 22% require surgical or image-guided intervention. 1

Step 4: Never rely on clinical assessment or laboratory values alone, as clinical determination of appendicitis has negative appendectomy rates as high as 25% without imaging. 2

Key Clinical Pitfalls

• Never exclude appendicitis based on absence of fever, as fever is absent in approximately 50% of appendicitis cases. 2
• Never delay CT beyond initial evaluation in patients with persistent or worsening symptoms, as early imaging prevents complications and identifies alternative surgical pathology. 1, 4
• Never discharge patients without establishing mandatory 24-hour follow-up and clear return precautions for worsening symptoms. 2
• In reproductive-age females, always obtain pregnancy test before CT and consider gynecologic causes as equally likely as appendicitis. 1