Central diabetes insipidus is characterised by-
**Core Concept**
Central diabetes insipidus (CDI) is a disorder of the posterior pituitary gland, resulting from a deficiency of the antidiuretic hormone (ADH), also known as vasopressin. This hormone plays a crucial role in regulating water reabsorption in the kidneys.
**Why the Correct Answer is Right**
In CDI, the decreased production or release of ADH leads to impaired water reabsorption in the collecting ducts of the kidneys. This results in an inability to concentrate urine, causing an excessive production of diluted urine. The patient experiences polyuria (excessive urine production) and polydipsia (excessive thirst). The kidneys are not able to concentrate urine due to the lack of ADH, which normally promotes water reabsorption.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not relevant to the pathophysiology of central diabetes insipidus.
* **Option B:** Hypernatremia can be a complication of CDI due to the excessive loss of water, but it is not the characteristic feature of the condition.
* **Option C:** This option is incorrect because it describes a different condition, nephrogenic diabetes insipidus, which is caused by the kidneys' inability to respond to ADH.
**Clinical Pearl / High-Yield Fact**
A key clinical feature of central diabetes insipidus is the presence of a concentrated urine osmolality in the presence of polyuria, which distinguishes it from nephrogenic diabetes insipidus.
**Correct Answer: C. Nephrogenic diabetes insipidus is characterised by an inability of the kidneys to respond to ADH, whereas central diabetes insipidus is caused by a deficiency of ADH secretion.**