Question: Encounter notes indicate that a patient suffers from “periarthritis NOS.” Is there a specific diagnosis code for this condition? Tennessee Subscriber Answer: Yes, there is, but you have to dig to find it. On your claim, report M77.9 (Enthesopathy, unspecified). Periarthritis NOS is listed as a condition that you’d code with M77.9. Other conditions that you’d report with M77.9 include: