Correct Answer: B

Rationale: The earliest changes observed by ophthalmoscope in background retinopathy of diabetes is typically the presence of microaneurysms. These are small dilations of retinal capillaries due to weakening of the vessel walls caused by diabetes-induced damage. Microaneurysms are a hallmark sign of diabetic retinopathy and are often the first visible sign on retinal examination. Other changes in diabetic retinopathy, such as venous dilatation, increased capillary permeability, and arteriovenous shunts, may develop later in the disease process as it progresses.

Correct Answer: B

Rationale: Prolactin levels can be increased by various factors, including chest wall trauma, pregnancy, and renal failure. However, hyperthyroidism is not typically associated with elevated prolactin levels. In fact, hyperthyroidism is more commonly associated with decreased levels of prolactin due to the inhibitory effect of thyroid hormones on prolactin secretion. Therefore, all of the options except for hyperthyroidism would be expected to increase prolactin levels.

Correct Answer: D

Rationale: Neurogenic diabetes insipidus is due to a deficiency in vasopressin (antidiuretic hormone, ADH) production in the hypothalamus or a failure of proper vasopressin release from the posterior pituitary. Causes of neurogenic DI typically involve factors affecting vasopressin synthesis, storage, or release. However, mutations in the vasopressin gene itself would be a cause of genetic forms of diabetes insipidus, not neurogenic diabetes insipidus. Common causes of neurogenic diabetes insipidus include traumatic brain injury, brain tumors, pituitary adenomas, meningitis, and Sheehan's syndrome.

Correct Answer: B

Rationale: Sheehan's syndrome, also known as postpartum hypopituitarism, is a condition characterized by pituitary gland dysfunction due to severe blood loss during childbirth, resulting in ischemic necrosis of the pituitary gland. As a consequence of pituitary hormone deficiency, one of the hallmark manifestations of Sheehan's syndrome is persistent lactation despite stopping breastfeeding. This occurs due to inadequate prolactin inhibition, leading to continuous milk production. Other common symptoms of Sheehan's syndrome include fatigue, weight loss, menstrual irregularities, hypothyroidism, adrenal insufficiency, and other pituitary hormone deficiencies. Cardiac failure, fever, and striking cachexia are not typical presentations associated with Sheehan's syndrome.

Correct Answer: D

Rationale: The overnight 1-mg dexamethasone suppression test is commonly used as an initial screening test for Cushing's syndrome. In this test, a patient takes 1 mg of dexamethasone orally at 11 p.m., and their serum cortisol level is measured the next morning. In patients with Cushing's syndrome, the cortisol levels will not be suppressed by the dexamethasone due to the presence of excessive cortisol production.