I77.6 vs M31.5
I77.6 and M31.5 can never be reported together. ICD-10-CM declares them mutually exclusive with an Excludes1 note, meaning the two conditions cannot occur in the same patient — so exactly one of them is correct for any given encounter.
I77.6
Arteritis, unspecified
BillableUnspecified
- Chapter 9
- Diseases of the circulatory system
- Section
- I70-I79
Use when the record says
- Aortitis NOS
- Endarteritis NOS
Indexed under
- Angiitis
- Aortitis (nonsyphilitic) (calcific)
- Arteriolitis
- Arteritis
- Endarteritis (bacterial, subacute) (infective)
M31.5
Giant cell arteritis with polymyalgia rheumatica
Billable
- Chapter 13
- Diseases of the musculoskeletal system and connective tissue
- Section
- M30-M36
Indexed under
- Polymyalgia › arteritica, giant cell
- Arteritis › giant cell NEC › with polymyalgia rheumatica
- Polymyalgia › rheumatica › with giant cell arteritis
These two codes sit in different chapters of the Tabular List, which is usually the clearest signal that they describe different underlying processes rather than different degrees of the same one.
Excludes1 is not always absolute: where two conditions covered by the note are genuinely unrelated, CMS guidance permits reporting both. Document the reasoning rather than assuming it. More on Excludes1 vs Excludes2 · FY2027