ICD-10 Code M05.40 – Rheumatoid myopathy with rheumatoid arthritis of unspecified site (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code M05.40 – Rheumatoid myopathy with rheumatoid arthritis of unspecified site
What it is
This code identifies rheumatoid arthritis with associated muscle disease, but the affected site is not specified. Use it when the record links myopathy directly to rheumatoid arthritis and no more precise site is documented.
Clinical signs
Findings may include proximal muscle weakness, reduced endurance, and functional difficulty with routine activities. Clinical features vary; refer to documentation for the specific muscle involvement and whether rheumatoid arthritis is active.
When to use this code
Use M05.40 when the provider documents rheumatoid myopathy as part of rheumatoid arthritis and does not name a specific joint or site. It also fits when the chart states rheumatoid arthritis with myopathy, but the location remains unspecified. Check documentation if the muscle disorder is described without a clear rheumatoid link.
Do not use for
Do not use this code for rheumatoid arthritis without myopathy, or for myopathy caused by another condition. If the site is specified elsewhere in the record, choose the more specific code instead.
Coding tip
Confirm that both rheumatoid arthritis and myopathy are documented together before assigning M05.40.