Pyogenic (bacterial) infection of the intervertebral disc located in the occipito-atlanto-axial region — spanning the articulations between the occiput, atlas (C1), and axis (C2).
Verified May 8, 2026 · 3 sources ↓
- Status
- Billable
- Chapter
- 13
- Related CPT
- 9
- Region
- Spine
Documentation tips
What should appear in the chart to support M46.31.
Source · Editorial brief grounded in 3 cited references ↓
- Specify the region by name — 'occipito-atlanto-axial' or 'C1–C2' — in the assessment to distinguish M46.31 from subaxial cervical codes like M46.32.
- Add a B95–B97 organism code whenever culture or sensitivity data is available; the M46.3 parent code carries a 'Use Additional' instruction that auditors will flag if missing.
- Document imaging findings (MRI signal change, endplate erosion, disc space narrowing, epidural involvement) to support medical necessity for both the diagnosis and any associated surgical or interventional procedures.
- Record any associated neurological deficits separately — myelopathy, radiculopathy, or cord compression codes are not bundled into M46.31 and should be listed as additional diagnoses.
- Note the source or presumed route of infection (hematogenous, post-procedural, contiguous) to support clinical context in the record, even though this distinction does not change the ICD-10 code.
Related CPT procedures
Procedure codes commonly billed with M46.31. 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 M46.31 and adjacent codes.
Source · Editorial brief grounded in CDC ICD-10-CM tabular guidance, AAOS coding references, and cited references ↓
- Using M46.31 when the infection spans multiple spinal levels beyond C1–C2 — if the occipito-atlanto-axial region plus other regions are all infected, M46.39 (multiple sites) is correct.
- Omitting the B95–B97 organism code — the parent code M46.3 carries an explicit 'Use Additional' instruction; claims without it may trigger a medical necessity or compliance flag.
- Confusing M46.31 with M46.4x (discitis, unspecified) — use M46.31 only when documentation specifies pyogenic (bacterial) etiology; unspecified or non-bacterial discitis maps elsewhere.
- Defaulting to a subaxial cervical code (M46.32, cervical region) when the infection is documented at C1–C2; the occipito-atlanto-axial region has its own distinct code.
- Failing to code associated epidural abscess or cord compression separately — M46.31 describes the disc infection only, not downstream structural or neurologic consequences.
Clinical context
Source · Editorial summary grounded in 3 cited references ↓
M46.31 identifies a bacterial discitis confined to the uppermost cervical spine: the occipito-atlanto-axial junction (occiput–C1–C2). This region is anatomically distinct from the subaxial cervical spine, and infection here carries significant risk of neurologic compromise due to proximity of the brainstem and spinal cord. Common causative organisms include Staphylococcus aureus, streptococcal species, and gram-negative rods in immunocompromised patients — use an additional code from B95–B97 to identify the infectious agent, per the Use Additional note on parent code M46.3.
This code applies whether the infection is hematogenous (the most common route), post-procedural, or secondary to contiguous spread from an adjacent abscess. It does not capture discitis of unspecified or mixed etiology; those map to M46.4x. If the infection involves multiple spinal regions, consider M46.39 instead, but only if the occipito-atlanto-axial region is also documented as infected.
In orthopaedic practice, M46.31 most commonly surfaces in the context of imaging workup (MRI with contrast is the gold standard), surgical consultation for drainage or stabilization, or intraoperative culture confirmation. Pair it with the organism code and any associated abscess or neurological deficit codes to fully represent the clinical picture and support medical necessity.
Sibling codes
Other billable codes under M46.3 (laterality / anatomic variants).
Frequently asked questions
Source · Generated from the editorial pipeline, verified against 3 cited references ↓
01What is the difference between M46.31 and M46.32?
02Do I need to add an organism code with M46.31?
03What if the infection involves both C1–C2 and lower cervical levels?
04Can M46.31 be used for post-procedural discitis at this level?
05What imaging documentation best supports M46.31?
06Is M46.31 appropriate when the causative organism has not yet been confirmed?
07Should I separately code associated myelopathy or cord compression?
Sources & references
Editorial content was developed using the following public sources. Last verified May 8, 2026.
- 01CDC ICD-10-CM Tabular List 2026 (effective Oct 1, 2025)
- 02icd10data.comhttps://www.icd10data.com/ICD10CM/Codes/M00-M99/M45-M49/M46-/M46.31
- 03aapc.comhttps://www.aapc.com/codes/icd-10-codes/M46.31
Mira AI Scribe
Mira AI Scribe captures the anatomic level (occiput/C1/C2), organism if cultured or suspected, MRI findings (endplate changes, disc signal, epidural extension), and any documented neurological deficits — preventing downcoding to unspecified discitis (M46.40), a missing organism code, or an audit flag for incomplete spinal level documentation.
See how Mira captures M46.31 documentation