Differential Diagnosis for Lower Abdominal Pain and Diarrhea

Given the symptoms of lower abdominal pain, lower peri-abdominal pain, diarrhea for 5 days that is getting better, no nausea or vomiting, a history of appendectomy, and a history of eating old food, the differential diagnosis can be categorized as follows:

• Single Most Likely Diagnosis
  • Gastroenteritis: This is likely due to the consumption of old food, which could be contaminated with bacteria, viruses, or other pathogens. The symptoms of diarrhea and abdominal pain are consistent with an infectious cause, and the fact that the symptoms are improving suggests a self-limiting condition.
• Other Likely Diagnoses
  • Irritable Bowel Syndrome (IBS): Although less likely given the acute onset, IBS could be considered if the patient has a history of similar episodes or if the symptoms persist beyond what is expected for an infectious cause.
  • Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease or ulcerative colitis could present with similar symptoms, especially if the patient has a history of such conditions. However, the acute onset and improvement with time make this less likely.
• Do Not Miss Diagnoses
  • Intestinal Obstruction: Although the patient has had an appendectomy, which reduces the risk of some causes of obstruction, other causes like adhesions or internal hernias could still occur. The absence of nausea and vomiting makes this less likely, but it's crucial to consider due to its potential severity.
  • Diverticulitis: Given the lower abdominal pain, diverticulitis is a possibility, especially in older adults. The history of eating old food is less directly related to this condition, but the pain location and nature warrant consideration.
  • Mesenteric Lymphadenitis: This condition can mimic appendicitis and could be considered in the differential, especially given the patient's history of appendectomy and the current symptoms.
• Rare Diagnoses
  • Yersiniosis: This bacterial infection can cause abdominal pain and diarrhea, and while it's less common, eating contaminated food could be a risk factor.
  • Giardiasis: An intestinal infection caused by the Giardia parasite, which could result from consuming contaminated food or water. It's less likely but should be considered in the appropriate clinical context.
  • Food Poisoning from Specific Pathogens: Depending on the type of old food consumed, specific types of food poisoning (e.g., Salmonella, E. coli) could be considered, though the improving nature of the symptoms might make these less likely.

Each diagnosis is considered based on the combination of symptoms, patient history, and potential exposures. The justification for each includes the match between symptoms and known presentations of the conditions, as well as the need to consider both common and less common but potentially serious diagnoses.