A 65-year-old man presents with weight loss, jaundice, and a palpable mass in the right upper quadrant. Laboratory tests reveal elevated bilirubin and alkaline phosphatase levels. What is the most likely diagnosis?

Correct Answer: C

Rationale: The most likely diagnosis for a 65-year-old man with weight loss, jaundice, palpable mass in the right upper quadrant, elevated bilirubin, and alkaline phosphatase levels is pancreatic cancer. This is because the symptoms and findings are classic for pancreatic cancer, which commonly presents with obstructive jaundice due to compression of the common bile duct by the tumor. Weight loss is also a common symptom of pancreatic cancer. Gallstones typically present with acute episodes of biliary colic, not a palpable mass. Hepatitis typically presents with elevated liver enzymes, but not a palpable mass. Primary biliary cirrhosis presents with chronic cholestasis and autoimmune features, not a palpable mass.

Correct Answer: A

Rationale: The most likely diagnosis is A: Primary biliary cirrhosis. Rationale: 1. Pruritus, jaundice, and xanthomas are classic symptoms of cholestatic liver disease. 2. Elevated cholesterol and alkaline phosphatase levels are characteristic of primary biliary cirrhosis. 3. Primary biliary cirrhosis is an autoimmune disease affecting small bile ducts, leading to liver damage. 4. Primary sclerosing cholangitis (B) presents with similar symptoms but typically affects larger bile ducts. 5. Gallstones (C) could cause jaundice but would not explain the elevated cholesterol levels. 6. Pancreatic cancer (D) may present with jaundice but is less likely given the specific lab findings.

Correct Answer: B

Rationale: The most likely diagnosis is Addison's disease (Choice B) because the symptoms match adrenal insufficiency. The low cortisol levels indicate adrenal cortex dysfunction, leading to fatigue and weight loss. Hyponatremia and hyperkalemia result from mineralocorticoid deficiency. Hyperpigmentation occurs due to elevated ACTH levels stimulating melanin production in Addison's. Cushing's syndrome (Choice A) presents with high cortisol levels, opposite to the low levels seen here. Hypothyroidism (Choice C) does not typically cause hyponatremia or hyperkalemia. Pheochromocytoma (Choice D) manifests with hypertension and catecholamine excess, not seen in this case.

Correct Answer: B

Rationale: The most likely diagnosis for the 70-year-old woman is Addison's disease. The symptoms of fatigue, anorexia, weight loss, darkened skin, along with hyponatremia, hyperkalemia, and low cortisol levels indicate adrenal insufficiency. Addison's disease is characterized by inadequate production of cortisol and aldosterone by the adrenal glands. The darkening of the skin, known as hyperpigmentation, is a classic sign of Addison's due to increased ACTH levels stimulating melanin production. In contrast, Cushing's syndrome presents with weight gain, hypertension, and high cortisol levels. Hypothyroidism typically presents with weight gain, cold intolerance, and constipation. Pheochromocytoma presents with hypertension, palpitations, and headaches due to excess catecholamine production. Therefore, the correct diagnosis in this case is Addison's disease.

Correct Answer: A

Rationale: The most likely diagnosis is A: Primary biliary cirrhosis. This condition typically presents with fatigue, pruritus, jaundice, elevated bilirubin, and alkaline phosphatase levels. The imaging findings of dilated intrahepatic bile ducts and a normal common bile duct are classic for primary biliary cirrhosis. It is an autoimmune disease affecting the bile ducts. Why other choices are incorrect: B: Primary sclerosing cholangitis presents with strictures and beading of bile ducts, not dilatation. C: Gallstones usually cause common bile duct obstruction, not intrahepatic dilation. D: Pancreatic cancer would typically present with different imaging findings and may involve the pancreatic duct, not just intrahepatic bile ducts.