Arthus phenomenon, sequela

This code describes the long-term effects or complications resulting from an Arthus reaction. An Arthus reaction is a localized type III hypersensitivity reaction characterized by immune complex deposition in blood vessel walls, leading to inflammation, necrosis, and tissue damage, typically occurring after repeated exposure to an antigen. "Sequela" indicates that the acute phase of the reaction has passed, and the code is used for residual conditions.

Use this code when documenting chronic skin changes, scarring, persistent pain, or other lasting tissue damage directly attributable to a past Arthus phenomenon. This applies when the patient is no longer experiencing the acute inflammatory phase but is being treated for the residual effects. This code is appropriate for follow-up encounters related to these long-term complications.

• Always use this code as a secondary diagnosis, following the code for the specific sequela (e.g., scar, chronic ulcer).
• Ensure documentation clearly links the current condition to a previous Arthus reaction.
• The "S" in the seventh character indicates sequela and is mandatory for this code.