M45.A2 identifies non-radiographic axial spondyloarthritis (nr-axSpA) localized to the cervical spine — an inflammatory spondyloarthropathy meeting clinical and MRI criteria for axSpA but lacking the structural sacroiliac changes visible on plain radiographs required for an ankylosing spondylitis diagnosis.

Documentation tips

What should appear in the chart to support M45.A2.

Source · Editorial brief grounded in 5 cited references ↓

• Physician must explicitly document 'non-radiographic axial spondyloarthritis' — do not infer the diagnosis from symptom descriptions alone; nr-axSpA requires a confirmed clinical diagnosis.
• Record that cervical region is the primary or documented site of involvement; if the note describes only lumbar or sacroiliac symptoms, a different M45.A subcode applies.
• Document the negative or non-diagnostic plain radiograph finding — this is the definitional separator from ankylosing spondylitis (M45.1–M45.9) and directly defends the nr-axSpA code selection on audit.
• Capture supporting diagnostic evidence in the note: MRI findings (bone marrow edema at cervical facets or vertebral endplates), HLA-B27 status, CRP/ESR levels, and duration/character of inflammatory-pattern neck pain.
• If a biologic agent (e.g., TNF inhibitor or IL-17 inhibitor) is being managed, document the medication and the nr-axSpA indication — payers may require diagnosis specificity for prior authorization and claim adjudication.
• Distinguish cervical region (C3–C7, coded M45.A2) from occipito-atlanto-axial region (C1–C2, coded M45.A1) and cervicothoracic region (M45.A3); the physician note should specify the spinal levels affected.

Related CPT procedures

Procedure codes commonly billed with M45.A2. Linking the right diagnosis to the right procedure is what establishes medical necessity.

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

Common coding pitfalls

The recurring mistakes coders make with M45.A2 and adjacent codes.

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

• Using M45.1 (ankylosing spondylitis of cervical region) instead of M45.A2 when radiographs are negative — these codes are mutually exclusive by definition; nr-axSpA requires absence of radiographic sacroiliitis meeting AS criteria.
• Defaulting to M45.A0 (unspecified sites) when the physician has documented cervical involvement — always assign the most specific regional subcode supported by documentation.
• Assigning M45.A2 based only on chronic neck pain or cervical spondylosis without a documented nr-axSpA diagnosis — this code requires a confirmed inflammatory diagnosis, not just a symptom.
• Failing to check Excludes1 at the M45 category level; coding M45.A2 alongside M02.3- or M08.1 in the same encounter is a tabular exclusion violation.
• Missing a multi-site code opportunity: if the physician documents cervical AND lumbar nr-axSpA involvement in the same encounter, M45.AB (multiple sites) may be more accurate than M45.A2 alone.
• Confusing cervical region (M45.A2) with cervicothoracic region (M45.A3) — the cervicothoracic junction is a distinct ICD-10 anatomic category; the physician note must specify spinal levels to assign correctly.

Clinical context

Source · Editorial summary grounded in 5 cited references ↓

Sibling codes

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