Reiter's disease, left knee

This code represents Reiter's disease, also known as reactive arthritis, specifically affecting the left knee. Reiter's disease is an autoimmune condition triggered by an infection, characterized by a triad of arthritis, urethritis, and conjunctivitis, though not all symptoms may be present. The arthritis in this case is localized to the left knee joint.

Use this code when documentation clearly indicates a diagnosis of Reiter's disease with inflammatory arthritis affecting the left knee. Supporting documentation should include physician notes detailing the diagnosis, location of arthritis, and potentially the underlying infection if identified. This code is appropriate for both initial and subsequent encounters related to the left knee involvement of Reiter's disease.

• Ensure the documentation specifies "left knee" to accurately assign this laterality-specific code.
• Consider coding any associated infectious trigger (e.g., Chlamydia, Shigella) as a secondary diagnosis, if documented.
• Differentiate from other forms of seronegative spondyloarthropathies or infectious arthritis affecting the knee.