**Question:** A 63-year-old asymptomatic woman is seen in the clinic for investigation of a persistently elevated alkaline phosphatase (ALP) level. The elevated ALP is an isolated finding and the remaining liver enzymes are normal. She reports no abdominal symptoms suggestive of biliary colic or hepatitis. On physical examination, the vital signs are normal, she is not icteric, the heart sounds are normal and the lungs are clear. The abdomen is soft and the liver span is 12 cm in the mid-clavicular line. X-rays of the pelvis show multiple porotic and sclerotic lesions with characteristic whorls of trabeculation. Her excretion of urinary hydroxyproline is also elevated. Which of the following is the most likely diagnosis?

A. Primary biliary cirrhosis
B. Primary liver cancer
C. Paget's disease
D. Secondary biliary cirrhosis

**Correct Answer:** C. Paget's disease

**Core Concept:**

Paget's disease is a chronic bone disorder characterized by abnormal bone remodeling, leading to increased bone resorption and formation. It results in bone pain, fractures, and a raised alkaline phosphatase (ALP) level, as seen in this case. In Paget's disease, the liver enzyme levels remain normal, unlike in conditions like primary liver cancer (option B) and biliary cirrhosis (options A and D).

**Why the Correct Answer is Right:**

In this scenario, the patient presents with elevated ALP levels and normal liver enzymes, and has no abdominal symptoms, jaundice, or ascites. The X-ray findings of multiple porotic and sclerotic lesions with whorls of trabeculation (option C) and elevated urinary hydroxyproline excretion support the diagnosis of Paget's disease.

**Why Other Options Are Incorrect:**

Primary biliary cirrhosis (option A) is characterized by a triad of chronic liver disease, jaundice, and portal hypertension. In contrast, the patient in question has normal liver enzymes and no clinical symptoms of portal hypertension.

Primary liver cancer (option B) is often associated with hepatitis and elevated liver enzymes. The patient does not have these signs or symptoms.

Secondary biliary cirrhosis (option D) is a result of primary liver disease, such as hepatitis, cholangitis, or cholestasis. The patient's normal liver enzymes and absence of abdominal symptoms, jaundice, and ascites rule out this option.

**Clinical Pearls:**

Paget's disease is a rare condition, affecting mainly the elderly, and can cause elevated ALP levels due to increased bone resorption and remodeling. The presence of multiple bone lesions and elevated hydroxyproline excretion help differentiate Paget's disease from other liver diseases.