**Core Concept**
Central diabetes insipidus (CDI) and nephrogenic diabetes insipidus (NDI) are two forms of inappropriate antidiuretic hormone (ADH) secretion. CDI is characterized by a deficiency of ADH, resulting in inadequate water reabsorption in the kidneys. NDI, on the other hand, is caused by a resistance to ADH, leading to impaired water reabsorption.

**Why the Correct Answer is Right**
In CDI, the lack of ADH results in an inability to concentrate urine, leading to excessive thirst and polyuria. In NDI, the kidneys are unable to respond to ADH, resulting in a similar presentation of polyuria and polydipsia. The kidneys' inability to concentrate urine is a hallmark of both conditions.

**Why Each Wrong Option is Incorrect**
**Option A:** This option should list a characteristic of CDI or NDI, such as polyuria, polydipsia, or hyponatremia.
**Option B:** This option should list a characteristic of CDI or NDI, such as polyuria, polydipsia, or hyponatremia.
**Option C:** This option should list a characteristic of CDI or NDI, such as polyuria, polydipsia, or hyponatremia.

**Clinical Pearl / High-Yield Fact**
A key difference between CDI and NDI is that CDI is often associated with a history of head trauma or surgery, whereas NDI is often seen in patients with chronic kidney disease or lithium toxicity.

**Correct Answer:** A
Inappropriate ADH secretion is characterized by hypernatremia, which is not seen in CDI or NDI.