A 40-year-old woman presents with fatigue, polyuria, and polydipsia. Laboratory tests reveal hyperglycemia and ketonuria. What is the most likely diagnosis?

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: 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.

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.