B27.9 vs G63
B27.9 and G63 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 G63
infectious mononucleosis complicated by polyneuropathy (B27.0-B27.9 with fifth character 1)
B27.9
Infectious mononucleosis, unspecified
Not billable
- Chapter 1
- Certain infectious and parasitic diseases
- Section
- B25-B34
G63
Polyneuropathy in diseases classified elsewhere
Billable
- Chapter 6
- Diseases of the nervous system
- Section
- G60-G65
Indexed under
- Neuritis › amyloid, any site (rheumatoid)
- Neuritis › gouty (rheumatoid)
- Neuropathy, neuropathic › uremic
- Neuropathy, neuropathic › vitamin B12
- Polyneuritis, polyneuritic › due to lack of vitamin NEC
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