ICD-10 Code M05.46 – Rheumatoid myopathy with rheumatoid arthritis of knee (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code M05.46 – Rheumatoid myopathy with rheumatoid arthritis of knee
What it is
This code identifies rheumatoid arthritis affecting the knee with associated rheumatoid myopathy. Use it when the record shows both inflammatory joint disease and muscle involvement linked to rheumatoid arthritis.
Clinical signs
Typical findings include knee pain, swelling, stiffness, and reduced range of motion, along with muscle weakness or myopathic changes. Clinical features vary; refer to documentation.
When to use this code
Use this code when the provider documents rheumatoid arthritis of the knee and specifically links myopathy to the rheumatoid condition. It is appropriate when the knee is the documented joint site and muscle involvement is part of the diagnosis. Check documentation if the site or relationship is unclear.
Do not use for
Do not use this code for rheumatoid arthritis without documented myopathy, or for knee pain from another cause. Do not assume rheumatoid myopathy unless the record clearly states it.
Coding tip
Verify that the knee involvement and the myopathy are both explicitly documented before assigning M05.46.