**Core Concept**
Reiter's syndrome, also known as reactive arthritis, is a type of spondyloarthritis characterized by a triad of clinical manifestations: urethritis, conjunctivitis, and arthritis. This condition typically follows a bacterial infection, often gastrointestinal or genitourinary.

**Why the Correct Answer is Right**
The correct answer is the one that does not belong to the classic triad of Reiter's syndrome. The pathophysiology of Reiter's syndrome is thought to be triggered by an abnormal immune response to the bacterial infection, leading to inflammation and joint damage. The condition often involves the HLA-B27 gene, which is a genetic marker for spondyloarthritis.

**Why Each Wrong Option is Incorrect**
* **Option A:** This is one of the classic symptoms of Reiter's syndrome, characterized by inflammation of the urethra, often accompanied by discharge and dysuria.
* **Option B:** This is another hallmark of Reiter's syndrome, involving inflammation of the conjunctiva, which can cause redness, discharge, and photophobia.
* **Option C:** This is the third component of the classic triad, involving inflammation of the joints, often affecting the knees, ankles, and feet.

**Clinical Pearl / High-Yield Fact**
Remember the classic triad of Reiter's syndrome: urethritis (A), conjunctivitis (B), and arthritis (C). This condition often follows a bacterial infection and is associated with the HLA-B27 gene.

**Correct Answer:** D