Differential Diagnosis

The patient's presentation of abdominal pain and a high heart rate above 110 bpm raises several possibilities. Here's a categorized differential diagnosis:

• Single most likely diagnosis:
  • Gastroenteritis: This condition is characterized by inflammation of the gastrointestinal tract, often due to infection, which can cause abdominal pain, vomiting, and a high heart rate due to dehydration and pain.
• Other Likely diagnoses:
  • Appendicitis: As mentioned, appendicitis can present with abdominal pain, initially diffuse or around the navel and then localizing to the lower right abdomen, and can be accompanied by a high heart rate due to pain and potential infection.
  • Urinary Tract Infection (UTI): A UTI, especially if it has ascended to the kidneys (pyelonephritis), can cause abdominal pain and a high heart rate due to the body's response to infection.
  • Diverticulitis: Inflammation of a diverticulum in the digestive tract can cause abdominal pain, usually on the lower left side, and can be associated with a high heart rate if there's significant pain or infection.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed):
  • Ectopic Pregnancy: Although less common, an ectopic pregnancy can present with abdominal pain and a high heart rate due to internal bleeding and should always be considered in women of childbearing age.
  • Intestinal Obstruction: This is a blockage that prevents the normal flow of the products of digestion, which can cause severe abdominal pain, vomiting, and a high heart rate due to dehydration and the body's response to the obstruction.
  • Perforated Viscus: A hole in the wall of the stomach or intestine can lead to peritonitis, an infection of the abdominal cavity, causing severe abdominal pain and a high heart rate due to infection and potential sepsis.
• Rare diagnoses:
  • Mesenteric Ischemia: A condition where there's insufficient blood flow to the intestine, which can cause severe abdominal pain out of proportion to the physical examination and can be associated with a high heart rate due to pain and the body's response to ischemia.
  • Pancreatitis: Inflammation of the pancreas can cause severe abdominal pain and a high heart rate due to the inflammatory response and potential infection.

Each of these diagnoses has a unique set of risk factors, symptoms, and signs that can help guide further evaluation and management. A thorough history, physical examination, and diagnostic tests (such as imaging and laboratory studies) are crucial for making an accurate diagnosis.