Non-radiographic axial spondyloarthritis confined to the lumbosacral region — inflammatory spondyloarthritis with active sacroiliitis on MRI or positive HLA-B27 but no definitive structural damage visible on plain radiograph.

Documentation tips

What should appear in the chart to support M45.A7.

Source · Editorial brief grounded in 5 cited references ↓

• The note must explicitly state 'non-radiographic' or document that sacroiliac joint X-rays do not meet modified New York criteria — without this, a reviewer cannot distinguish M45.A7 from AS.
• Record MRI findings supporting active sacroiliitis: bone marrow edema, periarticular inflammation, or other ASAS-defined positive MRI features in the lumbosacral region.
• Document HLA-B27 status — positive HLA-B27 is a key ASAS classification criterion and strengthens medical necessity for nr-axSpA-specific biologics.
• Specify 'lumbosacral region' by name in the assessment or impression; vague language like 'low back inflammatory arthritis' will not map cleanly to M45.A7 during audit.
• If the patient is on a biologic approved specifically for nr-axSpA, confirm the diagnosis code on prior authorization requests matches M45.A7 — payer systems may reject AS codes for nr-axSpA-labeled drugs.

Related CPT procedures

Procedure codes commonly billed with M45.A7. 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.A7 and adjacent codes.

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

• Assigning an ankylosing spondylitis code (M45.x) when the record documents no radiographic sacroiliitis — nr-axSpA and AS are mutually exclusive by definition; do not use M45.0–M45.9 for confirmed nr-axSpA.
• Using M45.A0 (unspecified sites) as a default when the provider has documented lumbosacral involvement — M45.A7 is the specific billable code and should be used whenever region is documented.
• Confusing M45.A6 (lumbar) with M45.A7 (lumbosacral) — if the provider documents sacral involvement alongside lumbar, M45.A7 is correct; lumbar-only maps to M45.A6.
• Failing to update the diagnosis code after reclassification — if a patient progresses from nr-axSpA to radiographic AS on follow-up imaging, the code must shift to the appropriate M45.x code at that encounter.
• Omitting a code for inflammatory bowel disease, psoriasis, or uveitis when documented as comorbid conditions — these are common extra-articular manifestations that should be coded additionally and support medical necessity.

Clinical context

Source · Editorial summary grounded in 5 cited references ↓

Sibling codes

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