G10 vs I02
G10 and I02 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 I02
Huntington's chorea (G10)
G10
Huntington's disease
Billable
- Chapter 6
- Diseases of the nervous system
- Section
- G10-G14
Use when the record says
- Huntington's chorea
- Huntington's dementia
Indexed under
- Huntington's disease or chorea
- Chorea › hereditary (chronic) (gravis) (posthemiplegic) (senile) (spasmodic)
- Chorea › Huntington's (chronic) (gravis) (posthemiplegic) (senile) (spasmodic)
- Disease, diseased › Huntington's
- Huntington's disease or chorea › with dementia
I02
Rheumatic chorea
Not billable
- Chapter 9
- Diseases of the circulatory system
- Section
- I00-I02
Use when the record says
- Sydenham's chorea
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