Non-radiographic axial spondyloarthritis localized to the thoracolumbar junction (T12–L1 region), confirmed by clinical criteria and MRI findings rather than plain radiographic sacroiliitis.

Documentation tips

What should appear in the chart to support M45.A5.

Source · Editorial brief grounded in 5 cited references ↓

• Document that plain radiographs do NOT show sacroiliitis meeting modified New York criteria — the absence of radiographic findings is what justifies nr-axSpA over ankylosing spondylitis.
• Record MRI findings explicitly: active bone marrow edema or structural lesions at the sacroiliac joints consistent with sacroiliitis, along with the spinal region(s) involved.
• Note HLA-B27 status, CRP/ESR values, and BASDAI score where available — payers reviewing biologic prior authorizations will look for this supporting data.
• Specify 'thoracolumbar region' (T12–L1 junction) by name in the assessment; vague documentation like 'mid-back and lower back pain' will not support M45.A5 over a nonspecific pain code.
• If the rheumatologist is managing the condition but the orthopedic provider is coding a related encounter, ensure the diagnosis is carried forward with the same specificity and supported by the shared record.

Related CPT procedures

Procedure codes commonly billed with M45.A5. 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.A5 and adjacent codes.

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

• Using M45.5 (ankylosing spondylitis of thoracolumbar region) when the patient has nr-axSpA — these are mutually exclusive; the distinction hinges on radiographic sacroiliitis, not symptom location.
• Defaulting to M45.A0 (unspecified sites) when the provider has documented thoracolumbar involvement — always code to the highest specificity the documentation supports.
• Reporting the non-billable parent code M45.A instead of the region-specific child code M45.A5 — claims submitted at the parent level will reject.
• Coding M46.8 for nr-axSpA after FY2022 — the dedicated M45.A subcategory replaced M46.8 as the appropriate home for nr-axSpA diagnoses.
• Failing to verify payer acceptance of M45.A5 — the code was new in FY2022 and some legacy payer systems may not have updated their tables; check remittance advice and re-submit with documentation if rejected.

Clinical context

Source · Editorial summary grounded in 5 cited references ↓

Sibling codes

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