A 45-year-old woman presents with fatigue, weight gain, and constipation. Laboratory tests reveal low TSH and high free T4 levels. What is the most likely diagnosis?

Correct Answer: B

Rationale: The correct answer is B: Hyperthyroidism. In this case, the low TSH and high free T4 levels indicate overproduction of thyroid hormones, leading to symptoms like fatigue, weight gain, and constipation. Low TSH is a result of negative feedback due to high T4 levels. Hyperthyroidism is characterized by an overactive thyroid gland, resulting in excess thyroid hormone production. Other choices are incorrect because hypothyroidism would show high TSH levels, thyroiditis typically presents with thyroid tenderness and inflammation, and thyroid cancer usually does not cause these hormonal imbalances.

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 for a 40-year-old woman presenting with fatigue, polyuria, polydipsia, hyperglycemia, and ketonuria is Type 1 diabetes mellitus. 1. Age: Type 1 diabetes commonly presents at a younger age. 2. Symptoms: Polyuria, polydipsia, fatigue are classic symptoms of uncontrolled diabetes. 3. Laboratory tests: Hyperglycemia and ketonuria indicate insulin deficiency. 4. Clinical presentation: Presence of ketonuria suggests metabolic derangement due to lack of insulin. In summary, Type 1 diabetes is the correct choice due to the age of the patient, symptoms, laboratory findings, and clinical presentation. Diabetes insipidus (choice C) presents with polyuria and polydipsia but lacks hyperglycemia and ketonuria. Type 2 diabetes (choice B) typically presents at an older age and rarely with ketonuria. Hyperthyroidism (choice D)

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.