Differential Diagnosis for Lymphocytosis and RLQ Pain

The patient presents with lymphocytosis and right lower quadrant (RLQ) pain, raising concerns for appendicitis among other potential diagnoses. The differential diagnosis can be categorized as follows:

• Single Most Likely Diagnosis
  • Appendicitis: This is the most likely diagnosis given the presentation of RLQ pain, which is a classic symptom of appendicitis. Lymphocytosis can occur in response to the inflammation caused by appendicitis.
• Other Likely Diagnoses
  • Mesenteric Lymphadenitis: This condition involves inflammation of the lymph nodes in the mesentery and can mimic appendicitis in its presentation, including RLQ pain and lymphocytosis.
  • Gastroenteritis: Certain viral or bacterial infections can cause gastroenteritis, leading to lymphocytosis and abdominal pain, which may be localized to the RLQ.
  • Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease or ulcerative colitis can present with abdominal pain, lymphocytosis, and may involve the RLQ.
• Do Not Miss Diagnoses
  • Intussusception: A condition where a part of the intestine telescopes into another, which can cause severe abdominal pain, including RLQ pain, and lymphocytosis due to intestinal obstruction and potential ischemia.
  • Ectopic Pregnancy: Although less common in patients without a clear history of pregnancy, ectopic pregnancy can present with abdominal pain and must be considered, especially if there's any possibility of pregnancy.
  • Ovarian Torsion: This is a gynecological emergency that can cause severe abdominal pain and may be associated with lymphocytosis due to the inflammatory response.
• Rare Diagnoses
  • Lymphoma: Abdominal lymphoma can cause lymphadenopathy, lymphocytosis, and abdominal pain, including in the RLQ, though it's less common than other causes of these symptoms.
  • Tuberculosis: Abdominal tuberculosis can involve the intestines, lymph nodes, or peritoneum, leading to abdominal pain, lymphocytosis, and other systemic symptoms.

Each of these diagnoses requires careful consideration based on the patient's full clinical presentation, including history, physical examination, laboratory results, and imaging studies.