Differential Diagnosis for Peritonitis

When considering the possibility of peritonitis, it's crucial to approach the diagnosis systematically, taking into account the patient's symptoms, medical history, and physical examination findings. The differential diagnosis can be organized into the following categories:

• Single Most Likely Diagnosis
  • Appendicitis: This is often the first consideration in cases of suspected peritonitis, especially if the patient presents with abdominal pain that initially is diffuse or around the navel and then localizes to the lower right quadrant. Appendicitis can lead to perforation, which in turn can cause peritonitis.
• Other Likely Diagnoses
  • Diverticulitis: Inflammation of the diverticula in the colon can lead to perforation and peritonitis, especially in older adults. Symptoms may include left lower quadrant pain, fever, and changes in bowel habits.
  • Gastrointestinal Perforation: Perforation of any part of the gastrointestinal tract (e.g., peptic ulcer disease) can lead to peritonitis. Patients may present with sudden onset of severe abdominal pain.
  • Cholecystitis: Inflammation of the gallbladder, usually due to gallstones, can lead to perforation and peritonitis. Right upper quadrant pain, fever, and leukocytosis are common findings.
• Do Not Miss Diagnoses
  • Ectopic Pregnancy: Although less common, a ruptured ectopic pregnancy can cause peritonitis and is a medical emergency. It typically presents with abdominal pain and vaginal bleeding in a woman of childbearing age.
  • Ovarian Torsion: This condition, often associated with ovarian cysts, can lead to necrosis and potentially peritonitis if not promptly treated. Sudden, severe pelvic pain is a hallmark symptom.
  • Mesenteric Ischemia: Ischemia of the bowel can lead to infarction and perforation, resulting in peritonitis. It's more common in older patients with cardiovascular disease and presents with severe abdominal pain out of proportion to physical findings.
• Rare Diagnoses
  • Spontaneous Bacterial Peritonitis (SBP): This condition occurs in the absence of an obvious source of infection, typically in patients with cirrhosis and ascites. Patients may present with fever, abdominal pain, and altered mental status.
  • Tuberculous Peritonitis: A form of extrapulmonary tuberculosis that affects the peritoneum, often presenting with chronic abdominal pain, ascites, and weight loss.
  • Familial Mediterranean Fever (FMF): A genetic disorder that can cause recurrent episodes of peritonitis, characterized by severe abdominal pain, fever, and sometimes chest or joint pain.

Each of these diagnoses requires careful consideration based on the patient's clinical presentation, laboratory findings, and imaging studies to ensure timely and appropriate management.