Question: Encounter notes indicate that a patient suffered from “allergic arthritis, R ankle.” Is this a misprint? If not, what is allergic arthritis and how should I code for this patient? Answer: No, it’s not a misprint. You’ll code allergic arthritis of the right ankle with M13.871 (Other specified arthritis, right ankle and foot). Condition explained: Allergic arthritis is arthritis that is triggered by certain food and medication, which can lead to joint inflammation and pain. The ICD-10 code is a little hard to find, as it is listed as a synonym under the M13.8- (Other specified arthritis) descriptor.