FY2027
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Excludes1 pair

A66.6 vs M25.4-

A66.6 and M25.4 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 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 (early) (late)
  • Hydrarthrosis › of yaws (early) (late)
  • 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