Rosh Internal Medicine Boost Practice Exam

A woman presenting with excessive thirst and nocturia after pituitary surgery is likely suffering from which condition?

1. Central diabetes insipidus

2. Nephrogenic diabetes insipidus

3. Primary polydipsia

4. Type 2 diabetes mellitus

The correct answer is: Central diabetes insipidus

The symptoms of excessive thirst and nocturia following pituitary surgery suggest a disorder related to antidiuretic hormone (ADH) deficiency. In this scenario, central diabetes insipidus is the most likely condition. After pituitary surgery, there can be damage to the pituitary gland or the hypothalamus, leading to a decreased secretion of ADH. This hormone plays a crucial role in the regulation of water balance in the body by promoting water reabsorption in the kidneys. When there is insufficient ADH, the kidneys cannot reabsorb water effectively, resulting in large volumes of dilute urine. This is precisely what leads to symptoms of excessive thirst (polydipsia) and nocturia, as the patient must frequently urinate and thus becomes dehydrated, driving the compensatory mechanism of increased fluid intake. While nephrogenic diabetes insipidus is characterized by a kidney's inability to respond to ADH, it is typically not a result of pituitary surgery. Moreover, primary polydipsia arises from excessive fluid intake rather than a hormonal deficiency. Type 2 diabetes mellitus would also not typically present with these specific symptoms following pituitary intervention. Thus, central diabetes insipidus is the most coherent diagnosis based on the patient's