FY2027
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Excludes1 pair

M85.8- vs Q78.2

M85.8 and Q78.2 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 M85.8
osteosclerosis fragilitas (generalista) (Q78.2)
M85.8

Other specified disorders of bone density and structure

Not billable
Chapter 13
Diseases of the musculoskeletal system and connective tissue
Section
M80-M85
Use when the record says
  • Hyperostosis of bones, except skull
  • Osteosclerosis, acquired
Indexed under
  • Osteopenia
  • Borderline › osteopenia
  • Osteopenia › borderline
  • Osteosclerosis › acquired
  • Disorder › bone › density and structure › specified type NEC
Q78.2

Osteopetrosis

Billable
Chapter 17
Congenital malformations, deformations, chromosomal abnormalities, and genetic disorders
Section
Q65-Q79
Use when the record says
  • Albers-Schönberg syndrome
  • Osteosclerosis NOS
Indexed under
  • Albers-Schönberg syndrome
  • Ivory bones
  • Osteopetrosis (familial)
  • Osteosclerosis
  • Disease, diseased › Albers-Schönberg (marble bones)

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