**Question:** A 75-year old woman with chronic atrial fibrillation presented to the hospital with a 2-day history of colicky abdominal pain. The physical examination revealed hypoactive bowel sounds and diffuse abdominal tenderness. Laboratory tests showed a white cell count of 19,400 per cubic millimeter with 92% neutrophils, a blood urea nitrogen level of 42 mg per deciliter (15 mmol per liter) and a serum creatinine level of 3.0 mg per deciliter (267 micromol per liter). The most probable diagnosis in this patient would be-

A. Sepsis
B. Acute appendicitis
C. Peritonitis
D. Acute myocardial infarction

**Correct Answer:**

**Core Concept:** The clinical presentation described in the question is highly suggestive of a peritonitic process, as evidenced by the patient's history of abdominal pain, hypoactive bowel sounds, and diffuse abdominal tenderness. These signs are commonly observed in conditions involving the peritoneum, such as peritonitis.

**Why the Correct Answer is Right:**

The patient's laboratory findings, including a white cell count of 19,400 per cubic millimeter with 92% neutrophils, elevated blood urea nitrogen (BUN) level of 42 mg/dL (15 mmol/L), and elevated serum creatinine level of 3.0 mg/dL (267 μmol/L), support the diagnosis of peritonitis or peritoneal inflammation. These laboratory values are consistent with a systemic inflammatory response and tissue damage, both of which are typical of peritonitis.

**Why Each Wrong Option is Incorrect:**

A. Sepsis: Although sepsis can present with systemic inflammation, the clinical features mentioned in the question are specific to peritonitis. The patient's age, abdominal pain, hypoactive bowel sounds, and tenderness are more consistent with peritonitis than sepsis.

B. Acute appendicitis: Although appendicitis can cause abdominal pain, the clinical features (hypoactive bowel sounds and abdominal tenderness) are more in line with peritonitis than acute appendicitis. Additionally, the elevated BUN and creatinine levels are not typical of appendicitis.

C. Acute myocardial infarction: The clinical features (hypoactive bowel sounds and abdominal tenderness) are more consistent with peritonitis than acute myocardial infarction. Elevated BUN and creatinine levels are not typical of a myocardial infarction.

D. Acute myocardial infarction: Similar to option C, the clinical features (hypoactive bowel sounds and abdominal tenderness) are more indicative of peritonitis than acute myocardial infarction. Elevated BUN and creatinine levels are not associated with myocardial infarction.

**Clinical Pearl:**

**Clinical Pearls:**

- Age-related abnormalities and elevated inflammatory markers (BUN, creatinine) are more suggestive of peritonitis than myocardial infarction.
- The patient's presentation with