Excludes1 pair
A86 vs A88-
A86 and A88 are not coded together. ICD-10-CM declares them mutually exclusive with an Excludes1 note — the two conditions are not expected to occur together, so exactly one of them is normally correct for a given encounter. The Official Guidelines carve out one exception: if the two conditions are clearly unrelated to each other, both may be reported.
The official note, declared on A88
viral encephalitis NOS (A86)
A86
Unspecified viral encephalitis
BillableUnspecified
- Chapter 1
- Certain infectious and parasitic diseases
- Section
- A80-A89
Use when the record says
- Viral encephalomyelitis NOS
- Viral meningoencephalitis NOS
Indexed under
- Encephalitis › acute
- Encephalitis › endemic (viral)
- Encephalitis › epidemic NEC (viral)
- Encephalitis › infectious NEC (acute) (virus)
- Encephalitis › postviral NEC
A88
Other viral infections of central nervous system, not elsewhere classified
Not billable
- Chapter 1
- Certain infectious and parasitic diseases
- Section
- A80-A89
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