ICD-10-CM · Spine

M46.35

Pyogenic (bacterial) infection of the intervertebral disc at the thoracolumbar junction, typically spanning the T12–L1 level, resulting in discitis caused by an identified or presumed bacterial organism.

Verified May 8, 2026 · 4 sources ↓

Status: Billable
Chapter: 13
Related CPT: 10
Region: Spine

Drawn from CDCICD10DataCMSAAPC

Documentation tips

What should appear in the chart to support M46.35.

Source · Editorial brief grounded in 4 cited references ↓

Document the spinal region by name — 'thoracolumbar' or 'T12–L1 junction' — not just 'lower thoracic' or 'upper lumbar,' which could map to adjacent-level codes.
Record MRI findings explicitly: T2 signal increase within the disc space, endplate erosion, and any paraspinal or epidural extension support M46.35 over unspecified discitis codes.
Identify the causative organism whenever possible; if blood or disc-space cultures are positive, add the appropriate B95–B97 code to specify the pathogen.
Document whether conservative treatment (IV antibiotics, bracing, rest) was attempted and failed if the encounter is heading toward surgical intervention — this supports medical necessity for fusion CPT codes.
Note systemic signs (fever, elevated ESR/CRP, leukocytosis) and any hematogenous source (recent procedure, IV drug use, bacteremia) to establish the pyogenic etiology in the record.

Related CPT procedures

Procedure codes commonly billed with M46.35. Linking the right diagnosis to the right procedure is what establishes medical necessity.

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

22558 $1,423.88

Anterior interbody arthrodesis of the lumbar spine using an anterior or anterolateral approach, including the minimal discectomy required to prepare the interspace for fusion.

22630 $1,510.72

Posterior interbody arthrodesis of a single lumbar interspace, including laminectomy and/or discectomy performed to prepare the interspace for fusion rather than for decompression.

22800 $1,312.99

Posterior spinal arthrodesis for deformity correction spanning up to 6 vertebral segments, with or without application of a body cast.

22840 $668.35

Posterior non-segmental instrumentation placed during spinal surgery, using rods, hooks, or wires that span multiple vertebral levels without anchoring at each intervening segment.

22842 $680.04

Posterior segmental spinal instrumentation spanning 3 to 6 vertebral segments, reported as an add-on to the primary spinal procedure code.

72148 $191.72

Non-contrast MRI of the lumbar spine used to evaluate disc pathology, spinal stenosis, nerve root compression, and other structural abnormalities without administration of contrast material.

72158 $318.31

MRI of the lumbar spinal canal and its contents performed first without contrast, then repeated after contrast administration for enhanced visualization.

20251 $421.19

Open surgical biopsy of the vertebral body, performed at the lumbar or cervical level, to obtain tissue for pathologic diagnosis.

63030 $898.15

Single-interspace lumbar laminotomy with nerve root decompression, including partial facetectomy, foraminotomy, and/or herniated disc excision performed via open surgical technique.

63047 $1,065.49

Lumbar laminectomy at a single vertebral segment that also includes facetectomy and foraminotomy for decompression of the spinal cord, cauda equina, and/or nerve roots — unilateral or bilateral.

Common coding pitfalls

The recurring mistakes coders make with M46.35 and adjacent codes.

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

Using M46.45 (discitis, unspecified, thoracolumbar region) when the provider has explicitly documented pyogenic or bacterial discitis — M46.35 is the correct, more specific code in that scenario.
Selecting M46.36 (lumbar region) or M46.34 (thoracic region) when documentation specifies the thoracolumbar junction (T12–L1); the junction has its own distinct code at M46.35.
Omitting the B95–B97 organism code when cultures are positive — pairing M46.35 with the pathogen code is required for maximum specificity and may affect DRG assignment.
Coding M54.5 (low back pain) or M54.6 (pain in thoracic spine) as the principal diagnosis when discitis is confirmed — the infection code must lead.
Confusing M46.25 (osteomyelitis of vertebra, thoracolumbar region) with M46.35 — osteomyelitis involves the vertebral body, while M46.35 is specific to the intervertebral disc space.

Clinical context

Source · Editorial summary grounded in 4 cited references ↓

M46.35 applies when a provider has documented pyogenic discitis or pyogenic disc infection specifically at the thoracolumbar region (T12–L1 junction). 'Pyogenic' is the operative word: use this code only when the infection is bacterial or presumed bacterial — not when etiology is unknown or unspecified (use M46.45 for unspecified discitis at this level). MRI findings consistent with discitis, elevated inflammatory markers, and positive blood or disc-space cultures all support this diagnosis and strengthen medical necessity.

This code appears on CMS's list of ICD-10-CM codes that support medical necessity for lumbar spinal fusion (CMS Article A56396), meaning it can anchor surgical authorization for instrumented stabilization when conservative management has failed. It maps to MS-DRG groups 539–541 (Osteomyelitis) and 456–458 (Spinal Fusion with infection), so accurate code assignment directly affects DRG weight and expected reimbursement.

When an organism is identified — e.g., Staphylococcus aureus confirmed on culture — assign an additional code from B95–B97 to specify the causative agent. Failure to add the organism code leaves clinical specificity on the table and may complicate infection-control and outcomes reporting. If infection spans multiple spinal regions, consider M46.39 (multiple sites) instead.

Sibling codes

Other billable codes under M46.3 (laterality / anatomic variants).

M46.37

Infection of intvrt disc (pyogenic), lumbosacral region

M46.36

Infection of intervertebral disc (pyogenic), lumbar region

M46.39

Infection of intvrt disc (pyogenic), multiple sites in spine

M46.32

Infection of intervertebral disc (pyogenic), cervical region

M46.38

Infection of intvrt disc (pyogenic), sacr/sacrocygl region

M46.34

Infection of intervertebral disc (pyogenic), thoracic region

M46.30

Infection of intervertebral disc (pyogenic), site unsp

M46.33

Infection of intvrt disc (pyogenic), cervicothor region

Frequently asked questions

Source · Generated from the editorial pipeline, verified against 4 cited references ↓

01What is the difference between M46.35 and M46.45?

M46.35 is pyogenic (bacterial) discitis at the thoracolumbar level; M46.45 is discitis of unspecified type at the same level. Use M46.35 when the provider has documented a bacterial or pyogenic etiology. If etiology is genuinely unknown, M46.45 is correct.

02Should I add a second code for the causative organism?

Yes. When a specific organism is identified — such as S. aureus on blood culture — assign an additional code from the B95–B97 range (bacterial and viral infectious agents) to specify the pathogen alongside M46.35.

03Does M46.35 support medical necessity for spinal fusion?

Yes. CMS Article A56396 (Lumbar Spinal Fusion) lists M46.35 as a code that supports medical necessity, placing it in MS-DRG 456–458 (spinal fusion with infection) when fusion is performed.

04What if the infection spans both the thoracolumbar and lumbar regions?

Use M46.39 (infection of intervertebral disc, pyogenic, multiple sites in spine) when documented infection involves more than one spinal region. Do not stack multiple single-level codes for contiguous multilevel disease unless each level is independently documented.

05Is M46.35 appropriate for fungal or tuberculous disc infection?

No. M46.35 is limited to pyogenic (bacterial) disc infection. Tuberculous spondylitis maps to A18.01, and fungal infections code elsewhere in the infectious disease chapter. The provider's documentation of organism type or clinical context drives the distinction.

06Which MS-DRGs does M46.35 map to?

M46.35 groups to MS-DRG 539–541 (Osteomyelitis, with/without CC/MCC) and MS-DRG 456–458 (Spinal Fusion except cervical with infection) under MS-DRG v43.0, per icd10data.com.

07Can M46.35 be the principal diagnosis on a surgical claim?

Yes. When the reason for the encounter is treatment of the pyogenic disc infection — whether surgical debridement, fusion, or inpatient IV antibiotic management — M46.35 is appropriate as the principal diagnosis.

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)
02
icd10data.com
https://www.icd10data.com/ICD10CM/Codes/M00-M99/M45-M49/M46-/M46.35
03
cms.gov
https://www.cms.gov/medicare-coverage-database/view/article.aspx?articleid=56396
04
aapc.com
https://www.aapc.com/codes/icd-10-codes/M46.35

Mira AI Scribe

Mira AI Scribe captures the documented spinal level (thoracolumbar / T12–L1), the qualifier 'pyogenic' or 'bacterial,' MRI findings (T2 disc signal, endplate erosion), culture results with organism identity, systemic infection markers (fever, CRP, ESR), and prior conservative management — preventing a downcode to unspecified discitis (M46.45), a missing organism code, or a generic pain code that would misrepresent the diagnosis and underweight the DRG.

See how Mira captures M46.35 documentation