Arthus phenomenon, initial encounter

This code represents a localized immune complex-mediated hypersensitivity reaction, specifically a type III reaction, characterized by inflammation and tissue damage at the site of antigen injection. It typically manifests as erythema, edema, and induration, often progressing to necrosis, due to the formation of antigen-antibody complexes that activate complement and attract inflammatory cells.

Use this code when documenting the initial presentation and treatment of an Arthus reaction, which often occurs after repeated subcutaneous or intradermal injections of an antigen, such as a vaccine or antitoxin. This code is appropriate for the first encounter where the condition is diagnosed and managed.

• Ensure documentation clearly states "initial encounter" for the Arthus phenomenon.
• Look for keywords like "localized immune complex reaction," "Type III hypersensitivity," or "Arthus reaction" in the clinical notes.
• Consider any associated symptoms or complications, such as necrosis, and code them separately if applicable.