A 35-year-old man presents with fatigue, weight loss, and hyperpigmentation of the skin. Laboratory tests reveal hyponatremia, hyperkalemia, and low cortisol levels. What is the most likely diagnosis?

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: 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.

Correct Answer: D

Rationale: The correct answer is D: Place the tablet under your tongue. Nitroglycerin is a vasodilator used to relieve chest pain in patients with MI. Placing the tablet under the tongue allows for rapid absorption through the oral mucosa, providing quick relief. Taking it with food (A) may delay absorption. Swallowing the tablet whole (B) would result in slower absorption through the GI tract. Taking it at bedtime (C) is not necessary for immediate relief of chest pain.