A66.6 vs M25.4
A66.6 and M25.4 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 M25.4
hydrarthrosis in yaws (A66.6)
A66.6
Bone and joint lesions of yaws
Billable
- Chapter 1
- Certain infectious and parasitic diseases
- Section
- A65-A69
Use when the record says
- Yaws ganglion
- Yaws goundou
- Yaws gumma, bone
- Yaws gummatous osteitis or periostitis
- Yaws hydrarthrosis
- Yaws osteitis
- Yaws periostitis (hypertrophic)
Indexed under
- Goundou
- Henpue, henpuye
- Ganglion › of yaws (compound) (diffuse) (joint) (tendon (sheath))
- Hydrarthrosis › of yaws
- Osteitis › due to yaws
M25.4
Effusion of joint
Not billable
- Chapter 13
- Diseases of the musculoskeletal system and connective tissue
- Section
- M20-M25
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