**Core Concept**
PANDAS is an acronym for Pediatric Autoimmune Neuropsychiatric Disorders Associated with Streptococcal Infections. It refers to a group of neuropsychiatric disorders that occur after a streptococcal infection, such as strep throat. The disorders are thought to be autoimmune in nature, where the immune system mistakenly attacks the brain.

**Why the Correct Answer is Right**
The most common psychiatric disorder associated with PANDAS is Obsessive-Compulsive Disorder (OCD). This is because the streptococcal infection triggers an autoimmune response that affects the basal ganglia and other brain regions involved in OCD. The resulting symptoms include intrusive thoughts, compulsions to perform specific rituals, and anxiety. The exact mechanism is not fully understood, but it is believed that the immune system produces antibodies against the streptococcal infection that also bind to the brain, disrupting normal function.

**Why Each Wrong Option is Incorrect**
**Option A:** While Tourette's Syndrome is a neuropsychiatric disorder that can be associated with PANDAS, it is not the most common disorder.
**Option B:** ADHD (Attention Deficit Hyperactivity Disorder) is not typically associated with PANDAS.
**Option C:** Anxiety disorders can be a part of PANDAS, but they are not the most common psychiatric disorder seen with this condition.

**Clinical Pearl / High-Yield Fact**
PANDAS is often misdiagnosed as a primary psychiatric disorder, leading to delayed treatment. Therefore, it is essential to consider a possible streptococcal infection in children with new-onset OCD or other neuropsychiatric symptoms.

**Correct Answer: C. Anxiety disorders.**