I77.6 vs M31.4
I77.6 and M31.4 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.
The official note, declared on I77.6
aortic arch (M31.4)
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)
M31.4
Aortic arch syndrome [Takayasu]
Billable
- Chapter 13
- Diseases of the musculoskeletal system and connective tissue
- Section
- M30-M36
Indexed under
- Takayasu's disease or syndrome
- Arteritis › aortic arch
- Arteritis › brachiocephalic
- Arteritis › young female aortic arch syndrome
- Disease, diseased › pulseless
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