M45Ankylosing spondylitis

M45 is the ICD-10-CM diagnosis code for ankylosing spondylitis. It belongs to block M45-M49 (spondylopathies) and chapter 13 (diseases of the musculoskeletal system and connective tissue). It is a header code, so it can't be reported by itself; one of its 11 subcodes must be used instead.

To report this condition, pick the subcode that matches the documentation: M45.0 (of multiple sites in spine), M45.1 (of occipito-atlanto-axial region), M45.2 (of cervical region), M45.3 (of cervicothoracic region), M45.4 (of thoracic region), M45.5 (of thoracolumbar region), M45.6 (lumbar region), M45.7 (of lumbosacral region) and 3 more.

Don't report M45 together with the conditions in its Excludes1 note: arthropathy in Reiter's disease (M02.3-) and juvenile (ankylosing) spondylitis (M08.1).

The conditions in its Excludes2 note aren't part of M45, but may be coded alongside it if the patient has both: Behçet's disease (M35.2).

It has been part of ICD-10-CM since the code set took effect on October 1, 2015 and hasn't changed since.