**Question:** Features of Reiter's disease are the following except?

A. Reactive arthritis
B. Infectious urethritis
C. Ocular involvement
D. Ankylosing spondylitis

**Core Concept:** Reiter's disease, also known as Reiter syndrome, is a form of reactive arthritis that develops following an infection (mainly urethritis, conjunctivitis, and enteritis) caused by certain pathogens, including Chlamydia trachomatis, Mycoplasma pneumoniae, and Epstein-Barr virus. It is characterized by three primary features:

**Why the Correct Answer is Right:**
Reiter's disease typically presents with three primary features: reactive arthritis, urethritis, and conjunctivitis. It is essential to understand the correct components of Reiter's disease in order to identify and diagnose the condition accurately.

Reiter's disease is caused by infections with certain pathogens, such as Chlamydia trachomatis, Mycoplasma pneumoniae, and Epstein-Barr virus. These pathogens lead to inflammation in the affected areas (reactive arthritis), urethritis, and conjunctivitis.

**Why Each Wrong Option is Incorrect:**

A. Ankylosing spondylitis: This is a separate entity characterized by chronic inflammation of the spine, sacroiliac joints, and peripheral joints. It is not a primary feature of Reiter's disease.

B. Infectious urethritis: This is a common feature in Reiter's disease, as it is often caused by sexually transmitted infections like Chlamydia trachomatis or Mycoplasma pneumoniae.

C. Ocular involvement: While conjunctivitis is a primary feature of Reiter's disease, ocular involvement can also occur in other conditions like Behçet's disease or uveitis, making it less specific to Reiter's disease.

D. Oral ulceration: Although oral ulcers can be present in Reiter's disease, they are not as specific to the condition as the other features.

**Clinical Pearl:** The correct identification of the primary features of Reiter's disease (reactive arthritis, urethritis, and conjunctivitis) is crucial for making an accurate diagnosis and initiating appropriate treatment. Reiter's disease is often caused by urethritis due to sexually transmitted infections or gastrointestinal infections, which can lead to arthritis and conjunctivitis.