**Core Concept**
Reiter's syndrome, also known as reactive arthritis, is a type of arthritis that occurs as a reaction to an infection elsewhere in the body, often in the gastrointestinal tract or the urogenital tract. It is characterized by a triad of symptoms: arthritis, urethritis, and conjunctivitis.

**Why the Correct Answer is Right**
Reiter's syndrome typically presents with a combination of urethritis, conjunctivitis, and arthritis, usually within a few weeks of an infection. The exact mechanism is not fully understood, but it is thought to be related to an abnormal immune response to the infection. The key features of Reiter's syndrome include:
* Urethritis: inflammation of the urethra, often presenting with dysuria (painful urination) and discharge.
* Conjunctivitis: inflammation of the conjunctiva, the thin membrane covering the white part of the eye and the inside of the eyelids.
* Arthritis: inflammation of the joints, often affecting the knees, ankles, and feet.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is likely incorrect because Reiter's syndrome typically presents with a combination of urethritis, conjunctivitis, and arthritis, not just a single symptom.
* **Option B:** This option is likely incorrect because the exact cause of Reiter's syndrome is not fully understood, but it is thought to be related to an abnormal immune response to an infection, not a direct result of the infection itself.
* **Option D:** This option is likely incorrect because Reiter's syndrome is a type of arthritis that occurs as a reaction to an infection, not a type of autoimmune arthritis.

**Clinical Pearl / High-Yield Fact**
It's essential to note that Reiter's syndrome is a type of reactive arthritis, which means it occurs as a reaction to an infection elsewhere in the body. This is in contrast to other types of arthritis, such as rheumatoid arthritis, which is an autoimmune disease.

**Correct Answer:** A.