ICD-10-CM · Spine

M45.3

Ankylosing spondylitis localized to the cervicothoracic junction, the transitional zone between the cervical and thoracic spine (roughly C7–T1).

Verified May 8, 2026 · 8 sources ↓

Status: Billable
Chapter: 13
Related CPT: 9
Region: Spine

Drawn from CDCICD10DataAAPCHealioAsahq

Documentation tips

What should appear in the chart to support M45.3.

Source · Editorial brief grounded in 8 cited references ↓

Specify 'cervicothoracic region' (C7–T1 junction) explicitly in the note — vague language like 'upper spine' or 'neck and upper back' does not map cleanly to M45.3.
Record radiographic findings that confirm AS: bilateral sacroiliitis grade ≥2 on plain X-ray, syndesmophytes, or bamboo spine appearance on imaging.
Document HLA-B27 status and inflammatory markers (CRP, ESR) to support the AS diagnosis in the medical record, even though ICD-10 does not require lab results for code selection.
If MRI shows active inflammation but X-ray is negative for sacroiliitis, the correct code is M45.A3, not M45.3 — document which modality was used and the findings.
Note the duration and character of symptoms (e.g., inflammatory back pain >3 months, morning stiffness, improvement with exercise) to differentiate AS from mechanical cervicothoracic disorders.

Related CPT procedures

Procedure codes commonly billed with M45.3. Linking the right diagnosis to the right procedure is what establishes medical necessity.

Source · CMS LCDs · AAOS specialty guidance · claims-pattern analysis

72040 $39.75

Radiologic examination of the cervical spine capturing two or three views (e.g., AP, lateral, oblique).

72050 $55.11

Radiologic examination of the cervical spine capturing a minimum of four views, used to evaluate alignment, fractures, degeneration, or other structural pathology of the neck.

72052 $62.79

Radiologic examination of the cervical spine using six or more distinct views, the highest-level plain-film cervical series in the CPT spine imaging family.

72148 $191.72

Non-contrast MRI of the lumbar spine used to evaluate disc pathology, spinal stenosis, nerve root compression, and other structural abnormalities without administration of contrast material.

97110 $29.06

Therapeutic exercise billed per 15-minute unit, targeting strength, endurance, range of motion, or flexibility with direct one-on-one patient contact.

20610 $68.81

Aspiration and/or injection of a major joint or bursa (shoulder, hip, knee, or subacromial bursa) performed without ultrasound guidance.

72156 View procedure details

77080 View procedure details

97530 View procedure details

Common coding pitfalls

The recurring mistakes coders make with M45.3 and adjacent codes.

Source · Editorial brief grounded in CDC ICD-10-CM tabular guidance, AAOS coding references, and cited references ↓

Reporting parent code M45 instead of M45.3 — M45 is non-billable and the claim will reject; always report to the full 4-character level.
Confusing M45.3 with M45.A3: M45.3 requires radiographic sacroiliitis; M45.A3 is for non-radiographic axial spondyloarthritis at the same spinal level — check which imaging was performed and what it showed.
Using M45.3 when disease involves multiple spinal regions; if the provider documents diffuse or multilevel AS involvement, M45.0 (multiple sites) is the correct code.
Applying M45.3 to juvenile patients — ankylosing spondylitis in patients under 16 is classified to M08.1, not the M45 series.
Coding M45.3 alongside M02.3– (Reiter's disease arthropathy) — the Excludes1 note prohibits reporting both codes for the same encounter.

Clinical context

Source · Editorial summary grounded in 8 cited references ↓

M45.3 is the correct code when a provider has documented radiographically confirmed ankylosing spondylitis (AS) with predominant or isolated involvement of the cervicothoracic region. AS is a chronic seronegative inflammatory arthropathy — also classified under rheumatoid arthritis of the spine — characterized by sacroiliitis, progressive vertebral ankylosis, and enthesitis. The cervicothoracic region designation is specific: if disease spans multiple spinal regions, use M45.0 (multiple sites). If the documented region is purely cervical, use M45.2; purely thoracic, use M45.4.

Key distinction from adjacent codes: M45.A3 covers non-radiographic axial spondyloarthritis of the cervicothoracic region — use that when MRI shows active sacroiliac inflammation but plain radiographs are negative for sacroiliitis. M45.3 requires radiographic evidence (bilateral grade ≥2 sacroiliitis on X-ray or established AS diagnosis). Never report parent code M45 alone — it is non-billable and claims will reject.

Excludes1 notes bar use of M45.3 when the underlying condition is Reiter's disease arthropathy (M02.3–) or juvenile ankylosing spondylitis (M08.1). Behçet's disease (M35.2) is an Excludes2, meaning it can be coded alongside M45.3 if both conditions coexist and are independently documented.

Sibling codes

Other billable codes under M45 (laterality / anatomic variants).

M45.1

Ankylosing spondylitis of occipito-atlanto-axial region

M45.0

Ankylosing spondylitis of multiple sites in spine

M45.6

Ankylosing spondylitis lumbar region

M45.2

Ankylosing spondylitis of cervical region

M45.8

Ankylosing spondylitis sacral and sacrococcygeal region

M45.9

Ankylosing spondylitis of unspecified sites in spine

M45.5

Ankylosing spondylitis of thoracolumbar region

M45.7

Ankylosing spondylitis of lumbosacral region

Frequently asked questions

Source · Generated from the editorial pipeline, verified against 8 cited references ↓

01What is the cervicothoracic region for M45.3 coding purposes?

The cervicothoracic region refers to the junction between the cervical and thoracic spine, centered on C7–T1. If the provider documents involvement of both cervical and thoracic levels, consider M45.0 (multiple sites) instead.

02When should I use M45.A3 instead of M45.3?

Use M45.A3 when the provider documents axial spondyloarthritis at the cervicothoracic level with MRI evidence of active sacroiliac inflammation but negative plain radiographs. M45.3 requires radiographically confirmed AS (sacroiliitis on X-ray or established bamboo spine findings).

03Can M45.3 be coded for a pediatric patient?

No. Juvenile ankylosing spondylitis (onset under age 16) is classified to M08.1. The M45 series, including M45.3, carries an Excludes1 note for juvenile cases — do not use M45.3 for pediatric patients.

04Can I report M45.3 and M35.2 (Behçet's disease) together?

Yes. Behçet's disease is listed as an Excludes2 under the M45 category, meaning both conditions may be coded simultaneously if independently documented and clinically distinct at the same encounter.

05What happens if I submit M45 instead of M45.3?

The claim will reject. M45 is a non-billable parent code. CMS and payers require the highest level of specificity; M45.3 is the valid billable code for cervicothoracic AS.

06Does M45.3 require a 7th character extension?

No. M-codes for musculoskeletal conditions do not use 7th-character extensions. The code M45.3 is complete as a 4-character code and requires no additional character.

07Which code do I use if AS involves both the cervicothoracic and thoracic regions?

Use M45.0 (ankylosing spondylitis of multiple sites in spine) when the provider documents disease spanning more than one spinal region. M45.3 is reserved for cervicothoracic region involvement only.

Sources & references

Editorial content was developed using the following public sources. Last verified May 8, 2026.

Mira AI Scribe

Mira AI Scribe captures the spinal region documented by the provider (cervicothoracic junction), the imaging modality and findings (X-ray sacroiliitis grade, syndesmophytes, or MRI active inflammation), HLA-B27 status, and inflammatory marker results. This prevents the scribe from defaulting to unspecified M45.9 when region-level specificity is available, and ensures the M45.3 vs. M45.A3 distinction is flagged before the claim is submitted.

See how Mira captures M45.3 documentation