**Core Concept**
Delusions are fixed, false beliefs that are not amenable to change in light of conflicting evidence. They are a characteristic feature of psychotic disorders such as schizophrenia.

**Why the Correct Answer is Right**
Delusions are a hallmark symptom of psychotic disorders, including schizophrenia. They are not present in mood disorders, anxiety disorders, or personality disorders, which are more commonly associated with cognitive distortions, misinterpretations, or maladaptive thinking patterns. In mood disorders, for example, patients may experience grandiose ideation or inflated self-esteem, but these are not the same as delusions. Delusions require a more profound disruption of thought processes, often involving a disconnection from reality.

**Why Each Wrong Option is Incorrect**
**Option A:** Delusions can be present in certain mood disorders, such as bipolar disorder, especially during manic episodes.
**Option B:** While anxiety disorders and personality disorders may involve maladaptive thinking patterns, they do not typically involve delusions.
**Option C:** Delusions are not present in neurodegenerative disorders such as Alzheimer's disease, which primarily involve cognitive decline and memory loss.

**Clinical Pearl / High-Yield Fact**
A useful way to distinguish delusions from other cognitive distortions is to ask the patient to provide evidence to support their belief. If they are unable to provide any logical or reasonable evidence, it may be a delusion.

**Correct Answer:** C. Delusions are not present in neurodegenerative disorders such as Alzheimer's disease.