ICD-10-CM · Spine

M45.A3

Inflammatory axial spondyloarthritis localized to the cervicothoracic spinal region (C7–T1 junction) in which structural damage — sacroiliitis or syndesmophytes — is absent on plain radiographs but may be detectable on MRI.

Verified May 8, 2026 · 3 sources ↓

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

Drawn from CDCICD10DataAAPC

Documentation tips

What should appear in the chart to support M45.A3.

Source · Editorial brief grounded in 3 cited references ↓

Explicitly document 'non-radiographic' status — note that X-rays do not meet modified New York criteria for sacroiliitis or vertebral structural damage.
Specify the cervicothoracic region by name or reference C7–T1 segment involvement; vague 'cervical spine' pain maps to M45.A2, not M45.A3.
Record MRI findings supporting active inflammation (bone marrow edema, Modic changes) even when X-ray is negative, to justify the nr-axSpA diagnosis under scrutiny.
Document HLA-B27 status, inflammatory back pain features, and duration of symptoms — payers often require these for biologic (TNFi, IL-17i) prior authorization linked to this code.
If the patient progresses to radiographic AS at the cervicothoracic level, update the diagnosis code to M45.3 and document the imaging change that triggered reclassification.

Related CPT procedures

Procedure codes commonly billed with M45.A3. Linking the right diagnosis to the right procedure is what establishes medical necessity.

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

99213 $95.19

Established patient office or outpatient visit requiring 20–29 minutes of total time or low-complexity medical decision-making.

99214 $135.61

Office visit for an established patient requiring moderate-complexity medical decision making (MDM), or 30–39 minutes of total provider time on the date of service.

99215 $192.39

Highest-level office or outpatient E/M visit for an established patient, qualifying via high-complexity medical decision making or 40–54 minutes of total provider time on the date of service.

72040 $39.75

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

72141 $190.72

MRI of the cervical spinal canal and its contents performed without contrast material.

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.

20610 $68.81

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

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.

72156 View procedure details

Common coding pitfalls

The recurring mistakes coders make with M45.A3 and adjacent codes.

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

Assigning M45.3 (ankylosing spondylitis, cervicothoracic) instead of M45.A3 when X-rays are negative — the two codes are mutually exclusive; use M45.A3 only while structural changes are absent on plain film.
Using M45.A0 (unspecified sites) when the provider has documented cervicothoracic involvement — always code to the highest specificity available.
Coding M45.A3 alongside M02.3– (Reiter's disease arthropathy) or M08.1 (juvenile ankylosing spondylitis) — both are Excludes1 and cannot appear on the same claim.
Applying a 7th-character extension to M45.A3 — M-codes in Chapter 13 do not use 7th-character trauma extensions; the code is complete as five characters.
Failing to update the code when disease progresses radiographically — continued use of M45.A3 after structural damage is confirmed on X-ray constitutes inaccurate diagnosis reporting.

Clinical context

Source · Editorial summary grounded in 3 cited references ↓

M45.A3 applies when a rheumatologist or spine specialist has diagnosed non-radiographic axial spondyloarthritis (nr-axSpA) with primary involvement at the cervicothoracic region, meaning the C7–T1 junction area. The defining feature is that conventional X-rays do not show the structural changes required for an ankylosing spondylitis (AS) diagnosis under modified New York criteria, yet the clinical and/or MRI picture is consistent with axial SpA. This distinction matters for coding because M45.A3 is the nr-axSpA code — not the AS code (M45.1–M45.9) — and conflating the two invites audit risk and payer denials, especially for biologic therapy authorizations that hinge on the specific diagnosis.

Use M45.A3 only when documentation explicitly names the region as cervicothoracic (or references C7–T1 segment involvement) and explicitly states non-radiographic status. If imaging later shows structural progression meeting AS criteria, reclassify to the corresponding ankylosing spondylitis code (M45.1 for occipito-atlanto-axial, M45.2 for cervical, M45.3 for cervicothoracic AS). When disease spans multiple spinal regions, consider M45.AB (multiple sites). For unspecified spinal site, use M45.A0.

Note the parent-code Excludes1 annotations: arthropathy in Reiter's disease (M02.3–) and juvenile (ankylosing) spondylitis (M08.1) cannot be coded with M45.A3. Behçet's disease (M35.2) is Excludes2, meaning it can coexist on the same claim when separately documented.

Sibling codes

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

M45.A4

Non-radiographic axial spondyloarthritis of thoracic region

M45.A1

Non-radiographic axial spondyloarthritis occipt-atlan-ax rgn

M45.A7

Non-radiographic axial spondyloarthritis of lumbosacr region

M45.A5

Non-radiographic axial spondyloarthritis of thrclm region

M45.A8

Non-radiographic axial spondyloarthritis sacr/sacrocygl rgn

M45.A0

Non-radiographic axial spondyloarthritis unsp site in spin

M45.A2

Non-radiographic axial spondyloarthritis of cervical region

M45.AB

Non-radiographic axial spondyloarthritis mult site in spine

Frequently asked questions

Source · Generated from the editorial pipeline, verified against 3 cited references ↓

01What is the difference between M45.A3 and M45.3?

M45.3 is ankylosing spondylitis of the cervicothoracic region — structural damage (sacroiliitis grade ≥2 bilaterally or grade 3–4 unilaterally) is visible on plain radiographs. M45.A3 is the non-radiographic variant: same region, same inflammatory disease, but X-rays do not yet show the structural threshold required for an AS diagnosis.

02Can M45.A3 be used before a rheumatologist confirms the diagnosis?

No. Axial SpA — radiographic or non-radiographic — requires specialist confirmation. An orthopedic coder should not assign M45.A3 based solely on a PCP's note about neck and upper back pain; there must be a documented clinical diagnosis from a provider qualified to render it.

03Which code applies when nr-axSpA affects both cervicothoracic and lumbar regions?

Use M45.AB (non-radiographic axial spondyloarthritis of multiple sites in spine) when two or more spinal regions are involved and documented. Do not stack individual site codes.

04Does M45.A3 require a 7th character?

No. M45.A3 is a five-character billable code with no 7th-character extension. Seventh-character requirements apply to injury codes (S-codes), not to Chapter 13 inflammatory spondylopathy codes.

05Is M45.A3 accepted for biologic drug prior authorizations?

Most commercial payers and Medicare Advantage plans accept nr-axSpA codes for TNF inhibitor and IL-17 inhibitor PAs, but requirements vary. Confirm the payer's LCD or coverage policy; some still require an AS (M45.x) code or additional clinical evidence such as elevated CRP or positive MRI for approval.

06When did M45.A3 become valid for billing?

M45.A3 was introduced as a new code in FY2022 ICD-10-CM (effective October 1, 2021). Claims with a date of service before that date must use the closest available prior-code equivalent. The FY2026 edition (effective October 1, 2025) retains the code without change.

07Can M45.A3 and M35.2 (Behçet's disease) appear on the same claim?

Yes. M35.2 is listed under Excludes2 at the M45 category level, meaning Behçet's disease and nr-axSpA can coexist and be coded together when both are separately documented and clinically distinct.

Sources & references

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

01CDC ICD-10-CM Tabular List 2026 (FY2026, effective October 1, 2025)
02
icd10data.com
https://www.icd10data.com/ICD10CM/Codes/M00-M99/M45-M49/M45-/M45.A3
03
aapc.com
https://www.aapc.com/codes/icd-10-codes/M45.A3

Mira AI Scribe

The Mira AI Scribe captures the spinal region by name (cervicothoracic/C7–T1), radiographic status (no structural changes on plain film), MRI inflammatory findings if present, HLA-B27 result, and the treating specialist's explicit nr-axSpA diagnosis. This specificity prevents downcoding to M45.A0 (unspecified) and protects biologic prior-authorization submissions that require the precise anatomic subcode.

See how Mira captures M45.A3 documentation