Differential Diagnosis for Lower Abdominal Pain and Diarrhea

Single Most Likely Diagnosis

• Viral Gastroenteritis: This is the most likely diagnosis given the patient's symptoms of lower abdominal pain, diarrhea, and a low-grade fever. Viral gastroenteritis is a common condition that can be caused by various viruses, including norovirus and rotavirus, and typically presents with these symptoms.

Other Likely Diagnoses

• Bacterial Gastroenteritis: Similar to viral gastroenteritis but caused by bacteria such as Salmonella, Shigella, or E. coli. The symptoms can be more severe and may include bloody stools.
• Inflammatory Bowel Disease (IBD) Flare: Conditions like Crohn's disease or ulcerative colitis can cause lower abdominal pain and diarrhea, especially if the patient has a history of IBD.
• Irritable Bowel Syndrome (IBS): Although IBS is a chronic condition, an acute exacerbation could present with these symptoms, especially if the patient has a history of IBS.

Do Not Miss Diagnoses

• Appendicitis: Although the pain is described as lower abdominal, appendicitis typically starts near the belly button and then moves to the lower right abdomen. It's crucial to consider appendicitis due to its potential for severe complications if not promptly treated.
• Diverticulitis: Inflammation of the diverticula in the colon can cause severe abdominal pain, usually on the lower left side, and changes in bowel habits. It's more common in older adults.
• Intestinal Obstruction: A blockage in the intestine can cause severe abdominal pain, vomiting, and changes in bowel habits. This is a medical emergency.
• Ectopic Pregnancy: In women of childbearing age, an ectopic pregnancy can cause lower abdominal pain and other symptoms. This is a life-threatening condition if not promptly diagnosed and treated.

Rare Diagnoses

• Intussusception: A condition where a part of the intestine slides into an adjacent part, causing bowel obstruction. It's rare in adults but can cause severe abdominal pain and changes in bowel habits.
• Mesenteric Lymphadenitis: Inflammation of the lymph nodes in the mesentery (the tissue that attaches the intestine to the back of the abdominal wall) can mimic appendicitis and cause lower abdominal pain.
• Yersiniosis: A bacterial infection caused by Yersinia enterocolitica, which can cause abdominal pain and diarrhea, and is more common in children but can occur in adults.