**Question:** A 42-year-old obese woman (BMI =32 kg/m2) presents with severe abdominal pain that radiates to the back. There is no history of alcohol or drug abuse. The blood pressure is 90/45 mm Hg, respirations are 32 per minute, and pulse is 100 per minute. Physical examination shows abdominal tenderness, guarding, and rigidity. An X-ray film of the chest shows a left pleural effusion. Laboratory studies reveal elevated serum amylase (850 U/L) and lipase (675 U/L), and hypocalcemia (7.8 mg/dL). Which of the following is the most likely diagnosis?

A. Acute pancreatitis
B. Acute cholecystitis
C. Acute appendicitis
D. Acute pyelonephritis

**Correct Answer:** **A. Acute pancreatitis**

**Core Concept:**
Acute pancreatitis is a condition characterized by inflammation of the pancreas, which can be triggered by various factors such as gallstones, alcohol consumption, or idiopathic causes. The clinical presentation typically includes abdominal pain, which is usually severe and radiating to the back, as observed in this case. Other symptoms like hypotension, tachycardia, and elevated serum amylase and lipase levels are also consistent with pancreatitis.

**Why the Correct Answer is Right:**
In this scenario, the patient presents with a history of severe abdominal pain, radiating to the back, hypotension, tachycardia, and elevated serum amylase and lipase levels. These symptoms and laboratory findings strongly indicate the presence of acute pancreatitis.

**Why Other Options are Incorrect:**

**B. Acute cholecystitis (Option B)** is incorrect because the patient's clinical presentation and laboratory values do not suggest a gallbladder-related condition. Gallstones may cause cholecystitis, but the abdominal pain is not typically radiating to the back, nor are there elevated serum amylase and lipase levels.

**C. Acute appendicitis (Option C)** is less likely because the patient's abdominal pain is severe and radiating to the back, which is atypical for appendicitis. Additionally, the elevated serum amylase and lipase levels are not consistent with appendicitis.

**D. Acute pyelonephritis (Option D)** is incorrect as well. The patient's clinical presentation and laboratory values do not suggest a urinary tract infection. The elevated serum amylase and lipase levels are not consistent with pyelonephritis. Furthermore, pyelonephritis typically presents with flank pain, which is not mentioned in the patient's history or examination findings.

**Clinical Pearl:**

When assessing patients with acute abdominal pain, clinicians should consider the possibility of acute pancreatitis, especially in cases with radiating back pain, hypotension, tachycardia, and elevated serum amylase and lipase levels. Acute pancreatitis is a common differential diagnosis in cases of severe abdominal pain.