ICD-10-CM · Spine

M46.51

Infectious inflammation of the spinal structures at the occipito-atlanto-axial region (C0–C1–C2 junction) caused by a pathogen not classified elsewhere in the M46 category.

Verified May 8, 2026 · 5 sources ↓

Status: Billable
Chapter: 13
Related CPT: 8
Region: Spine

Drawn from CDCICD10DataAAPCFindacode

Documentation tips

What should appear in the chart to support M46.51.

Source · Editorial brief grounded in 5 cited references ↓

Explicitly name the anatomical region as 'occipito-atlanto-axial,' 'C0–C1–C2,' or 'upper cervical' — generic 'cervical spine infection' defaults to an unspecified or cervical-region code.
Record the infective basis: positive blood cultures, ESR/CRP values, MRI signal abnormality (T2 hyperintensity, contrast enhancement), or biopsy/aspiration results confirming infection.
Assign a causative-organism code (B95–B97 for bacterial/viral agents or appropriate A-code for specific infections such as tuberculosis or brucellosis) alongside M46.51 per ICD-10-CM Code Also convention.
Document any neurologic findings (myelopathy, radiculopathy, instability) that may drive additional codes and support medical necessity for surgical or advanced interventional procedures.
Note prior antibiotic therapy, duration of symptoms, and failed conservative management to support inpatient-level or surgical care medical necessity.

Related CPT procedures

Procedure codes commonly billed with M46.51. Linking the right diagnosis to the right procedure is what establishes medical necessity.

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

22595 $1,499.03

Posterior arthrodesis of the atlas and axis (C1-C2), surgically fusing the first and second cervical vertebrae through a posterior approach to stabilize the upper cervical spine.

22548 $1,943.60

Arthrodesis of the clivus-C1-C2 complex via anterior transoral or extraoral approach, with or without odontoid process excision.

22600 $1,282.93

Posterior or posterolateral cervical spinal fusion at a single interspace below C2, performed through a posterior approach to achieve bony arthrodesis.

72141 $190.72

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

20225 $364.74

Percutaneous bone biopsy using a trocar or needle targeting deep skeletal structures such as the vertebral body or femur.

72040 $39.75

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

72125 View procedure details

61001 View procedure details

Common coding pitfalls

The recurring mistakes coders make with M46.51 and adjacent codes.

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

Submitting the non-billable parent M46.5 instead of the site-specific M46.51 — payers will reject or downcode the claim.
Omitting the causative-organism code; ICD-10-CM instructs 'Code Also' for the infectious agent, and its absence is an audit flag.
Confusing M46.51 with M46.41 (Discitis, unspecified, occipito-atlanto-axial region) — if the infection is specifically isolated to the disc space and no organism is identified, discitis unspecified may be more appropriate; when an infectious etiology is confirmed, M46.51 is correct.
Using M46.51 for vertebral osteomyelitis at C1–C2 — osteomyelitis maps to M46.21 (Osteomyelitis of vertebra, occipito-atlanto-axial region), not M46.51.
Defaulting to an unspecified cervical region code when the clinical record clearly localizes the infection to the C0–C1–C2 level — specificity is required and supported when imaging or surgical reports identify the occipito-atlanto-axial region.

Clinical context

Source · Editorial summary grounded in 5 cited references ↓

M46.51 applies to infections of the upper cervical spine — specifically the occiput, atlas (C1), and axis (C2) — that do not fall under more specific infective spondylopathy codes (e.g., vertebral osteomyelitis, which maps to M46.2x). Use it when the documented diagnosis is an infectious process of the occipito-atlanto-axial spinal region and the causative organism or condition doesn't drive you to a more specific code elsewhere in the M46 or M00–M02 range. Common scenarios include pyogenic spondylitis, granulomatous infections, or post-surgical infections localized to C0–C2.

Because this region is mechanically unique — the atlantoaxial and atlantooccipital joints govern most head rotation and flexion — infections here carry risk of instability, myelopathy, and atlantoaxial subluxation. Payers scrutinize upper cervical infection diagnoses closely; documentation must establish the anatomical region by name and link it to objective findings (MRI signal changes, ESR/CRP elevation, positive cultures, or biopsy). Code Also any identified organism using B95–B97 or A00–B94 as applicable.

M46.51 sits under the non-billable parent M46.5 (Other infective spondylopathies). Do not submit M46.5 for reimbursement — always code to the highest specificity. If the site is genuinely unknown, use M46.50. If multiple spinal regions are affected, review whether M46.59 (multiple sites) better reflects the documented extent of disease.

Sibling codes

Other billable codes under M46.5 (laterality / anatomic variants).

M46.53

Other infective spondylopathies, cervicothoracic region

M46.55

Other infective spondylopathies, thoracolumbar region

M46.59

Other infective spondylopathies, multiple sites in spine

M46.58

Oth infective spondylopathies, sacr/sacrocygl region

M46.50

Other infective spondylopathies, site unspecified

M46.54

Other infective spondylopathies, thoracic region

M46.57

Other infective spondylopathies, lumbosacral region

M46.52

Other infective spondylopathies, cervical region

Frequently asked questions

Source · Generated from the editorial pipeline, verified against 5 cited references ↓

01What distinguishes M46.51 from M46.41?

M46.41 is discitis of unspecified etiology at the occipito-atlanto-axial region. M46.51 is used when an infectious cause has been established. If the provider documents confirmed or suspected infection as the basis for the disc/vertebral inflammation at C0–C2, M46.51 is the correct choice.

02Should I also code the causative organism when using M46.51?

Yes. ICD-10-CM instructs coders to 'Code Also' the infectious agent. Add the appropriate B95–B97 code for common bacteria or viruses, or a specific A-code (e.g., A18.01 for spinal tuberculosis) when the organism is identified. Omitting this is a common audit trigger.

03Can M46.51 be used for vertebral osteomyelitis at C1–C2?

No. Vertebral osteomyelitis at the occipito-atlanto-axial level maps to M46.21. Reserve M46.51 for other infective spondylopathies — infectious processes involving the spinal structures at C0–C2 that are not classified as osteomyelitis.

04What imaging documentation supports M46.51?

MRI with and without contrast is the primary modality — document T2 signal hyperintensity, epidural or paraspinal enhancement, or end-plate changes at C0–C2. CT findings of bone erosion or destruction and nuclear medicine scan results (if performed) also support the diagnosis.

05Is M46.51 appropriate for post-surgical infections at the occipito-atlanto-axial level?

It can be used for infectious spondylopathy following surgery when the residual spinal infection is the primary diagnosis being coded. However, if the encounter is specifically for a post-procedural complication, review whether a complication code (T84.6x series or similar) should be sequenced first per ICD-10-CM guidelines.

06When should I use M46.50 instead of M46.51?

Use M46.50 only when the site of the infective spondylopathy is genuinely not documented or cannot be determined. If the clinical record identifies the C0–C2 level by imaging, surgical report, or provider notation, M46.51 is required for maximum specificity.

Sources & references

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

01CDC ICD-10-CM Tabular List 2026 (effective October 1, 2025)
02
icd10data.com
https://www.icd10data.com/ICD10CM/Codes/M00-M99/M45-M49/M46-/M46.51
03
aapc.com
https://www.aapc.com/codes/icd-10-codes/M46.5
04
findacode.com
https://www.findacode.com/icd-10-cm/icd-10-cm-diagnosis-codes-M46-group.html
05
cdc.gov
https://www.cdc.gov/nchs/icd/icd-10-cm/index.html

Mira AI Scribe

Mira AI Scribe captures the anatomical level (occipito-atlanto-axial/C0–C2), confirmation of infectious etiology (MRI findings, lab values, culture results), identified organism if available, and any neurologic compromise — preventing a drop to the unspecified M46.50 and flagging the missing organism code before the claim is submitted.

See how Mira captures M46.51 documentation