Gastroenteritis or Inflammatory Bowel Disease (IBD) with lymphadenopathy: This is a common cause of abdominal pain and can be associated with enlarged inguinal lymph nodes due to the body's immune response to the infection or inflammation.

Diverticulitis: Inflammation of the diverticula in the digestive tract can cause abdominal pain and may lead to lymphadenopathy, including enlargement of inguinal lymph nodes, especially if the infection spreads.
Appendicitis: Although appendicitis typically presents with right lower quadrant pain, it can sometimes cause more generalized abdominal pain and may be associated with lymph node enlargement.
Inguinal Hernia with Incarceration or Strangulation: An inguinal hernia can cause abdominal pain and enlarged inguinal lymph nodes if it becomes incarcerated or strangulated, leading to an inflammatory response.

Testicular Cancer with Metastasis: Testicular cancer can metastasize to the inguinal lymph nodes, causing enlargement. Although less common, missing this diagnosis could be catastrophic.
Lymphoma: Both Hodgkin's and non-Hodgkin's lymphoma can present with lymphadenopathy, including inguinal lymph nodes, and abdominal pain due to involvement of abdominal lymph nodes or other organs.
Abdominal Aortic Aneurysm (AAA): An AAA can cause abdominal pain and, if it ruptures, can lead to a severe inflammatory response that might involve the lymph nodes.

Kaposi's Sarcoma: This rare cancer can cause lymphadenopathy and abdominal pain, especially in immunocompromised patients.
Castleman Disease: A rare disorder that involves an overgrowth of cells in the lymph nodes, which can cause lymphadenopathy and systemic symptoms including abdominal pain.
Whipple's Disease: A rare, systemic bacterial infection that can cause abdominal pain, weight loss, and lymphadenopathy, among other symptoms.