Professional and Linguistic Assessments Board (PLAB) Practice Exam

What syndrome is associated with the loss of negative feedback to the pituitary after surgical removal of the adrenal glands?

1. Syndrome of inappropriate antidiuretic hormone secretion (SIADH)

2. Nelson's syndrome

3. Secondary adrenal insufficiency

4. Addison's disease

The correct answer is: Nelson's syndrome

The correct answer is associated with Nelson's syndrome, which occurs after the surgical removal of the adrenal glands (adrenalectomy). The adrenal glands produce hormones like cortisol that exert negative feedback on the pituitary gland, inhibiting the secretion of adrenocorticotropic hormone (ACTH). When the adrenal glands are removed, this feedback loop is disrupted. As a result, ACTH levels can rise in response to the lack of cortisol, leading to hyperplasia of the pituitary gland and increased production of ACTH. This condition is characterized by the presence of an ACTH-secreting pituitary adenoma and can lead to hyperpigmentation of the skin due to increased production of melanocyte-stimulating hormone (MSH), which is derived from the same precursor as ACTH. Understanding how the feedback mechanisms work is crucial for recognizing why the absence of adrenal hormones leads to this condition. The other options reflect different mechanisms and conditions pertaining to hormone regulation and deficiencies. For instance, secondary adrenal insufficiency refers to inadequate ACTH response and is usually due to pituitary issues, and Addison's disease is characterized by primary adrenal insufficiency where there is a direct loss of adrenal function. Syndrome of inappropriate antidiuretic hormone secretion (SIADH)