Which of the following is a characteristic manifestation of Addison's disease?

A. Hyperpigmentation of the skin. Addison's disease involves primary adrenal insufficiency, which triggers a compensatory increase in adrenocorticotropic hormone (ACTH) from the pituitary. High levels of ACTH stimulate melanocytes, leading to a "bronzed" or tan appearance of the skin and mucous membranes. This is a classic diagnostic sign that distinguishes primary from secondary adrenal insufficiency. B. Hypertension. Addison's disease causes a deficiency in aldosterone, which leads to the loss of sodium and water in the urine. This results in hypovolemia and significant hypotension, often manifesting as orthostatic changes or circulatory collapse. Hypertension is more characteristic of Cushing's syndrome or a pheochromocytoma rather than the adrenal failure seen in Addison's. C. Weight gain. The lack of cortisol in Addison's disease leads to impaired metabolism, anorexia, and chronic nausea. Most patients experience significant weight loss and muscle wasting due to the loss of glucocorticoid and mineralocorticoid effects. Weight gain and "moon face" are symptoms of cortisol excess, not the adrenal deficiency characteristic of this condition. D. Excessive thirst. While patients may lose fluid, the primary manifestation is a "salt craving" due to hyponatremia from aldosterone deficiency. Excessive thirst and polyuria are more commonly associated with diabetes mellitus or diabetes insipidus. In Addison's, the focus is on the loss of salt and the resulting low blood pressure and hyperkalemia.