A 60-year-old woman presents with pruritus, jaundice, and xanthomas. Laboratory tests reveal elevated cholesterol and alkaline phosphatase levels. What is the most likely diagnosis?

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 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.

Correct Answer: B

Rationale: The correct answer is B: Hyperthyroidism. In this case, the low TSH and high free T4 levels indicate an overactive thyroid gland, leading to symptoms like fatigue, weight gain, and constipation. The low TSH is due to negative feedback as the high free T4 suppresses TSH production. Hyperthyroidism fits this clinical picture, as opposed to hypothyroidism (choice A) which would have high TSH and low free T4 levels. Thyroiditis (choice C) typically presents with symptoms of both hyperthyroidism and hypothyroidism and is usually transient. Thyroid cancer (choice D) is less likely given the presentation of symptoms and specific lab results.

Correct Answer: C

Rationale: The most likely diagnosis is Crohn's disease (Choice C). This is supported by the symptoms of abdominal pain, diarrhea, weight loss, mouth ulcers, and perianal fistula, which are characteristic of Crohn's disease. These symptoms are not typically seen in irritable bowel syndrome (Choice B) or diverticulitis (Choice D). While ulcerative colitis (Choice A) may also present with similar symptoms, the presence of perianal fistula and mouth ulcers is more indicative of Crohn's disease. Crohn's disease is a chronic inflammatory condition that can affect any part of the gastrointestinal tract, leading to the diverse range of symptoms seen in this patient.