ICD-10-CM · Spine

M46.46

M46.46 designates inflammation of an intervertebral disc in the lumbar region (L1–L5) where the causative organism has not been identified or specified in the clinical record.

Verified May 8, 2026 · 7 sources ↓

Status: Billable
Chapter: 13
Related CPT: 9
Region: Spine

Drawn from CDCICD10DataIcdcodesAAPCGenhealth

Documentation tips

What should appear in the chart to support M46.46.

Source · Editorial brief grounded in 7 cited references ↓

Explicitly state 'lumbar region' or list the affected vertebral level(s) (L1–L5) — 'back pain with disc inflammation' alone won't support M46.46 over M46.40.
Record MRI findings verbatim: T2 signal hyperintensity in the disc, endplate erosion, and any paraspinal soft-tissue changes that confirm discitis rather than degenerative disc disease.
Document ESR and CRP values with dates; payers and auditors use lab thresholds (ESR >40 mm/hr, CRP >20 mg/L) as clinical validation anchors for infectious/inflammatory disc diagnoses.
If blood cultures, disc aspirate, or biopsy identify an organism, name it in the note and add the corresponding causative-organism code (e.g., B95.61 for S. aureus) — the M46 category carries a 'use additional code' instruction.
Note prior treatment history (antibiotics, bracing, prior imaging) to support medical necessity for advanced imaging or surgical intervention billed alongside this diagnosis.

Related CPT procedures

Procedure codes commonly billed with M46.46. Linking the right diagnosis to the right procedure is what establishes medical necessity.

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

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.

72141 $190.72

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

99213 $95.19

Established patient office or outpatient visit requiring 20–29 minutes of total time or low-complexity medical decision-making.

99214 $135.61

Office visit for an established patient requiring moderate-complexity medical decision making (MDM), or 30–39 minutes of total provider time on the date of service.

99215 $192.39

Highest-level office or outpatient E/M visit for an established patient, qualifying via high-complexity medical decision making or 40–54 minutes of total provider time on the date of service.

20225 $364.74

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

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.

72020 $23.71

Single-view radiologic examination of the spine at a specified level.

Common coding pitfalls

The recurring mistakes coders make with M46.46 and adjacent codes.

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

Defaulting to M46.40 (unspecified site) when the provider clearly documents lumbar involvement — always assign M46.46 when lumbar region is specified.
Omitting the causative-organism ancillary code when microbiology results are available in the same encounter record, leaving revenue and clinical accuracy on the table.
Confusing discitis (disc space inflammation) with osteomyelitis (M86.06, vertebral body involvement) — if both disc and vertebral body are infected, evaluate whether a dual code assignment is appropriate rather than using M46.46 alone.
Using M46.46 for degenerative disc disease with inflammatory features — this code is reserved for confirmed disc space infection or inflammation, not routine spondylosis or Modic changes without infectious etiology.
Failing to differentiate lumbar (M46.46) from lumbosacral (M46.47) when the MRI report specifies L5–S1 disc involvement; lumbosacral level maps to M46.47, not M46.46.

Clinical context

Source · Editorial summary grounded in 7 cited references ↓

Use M46.46 when the provider documents discitis localized to the lumbar spine and the chart does not specify the infectious or causative organism. The 'unspecified' qualifier in this code refers to the etiology, not the anatomic region — lumbar location is already built into the sixth character (6). If organism identification is later confirmed (e.g., S. aureus on blood culture or biopsy), add ancillary code B95.61 (S. aureus) alongside M46.46 to satisfy the 'use additional code' instruction from the M46 category.

Clinical validation typically requires MRI demonstrating T2 hyperintensity within the disc and endplate erosion, supported by inflammatory markers — ESR >40 mm/hr and CRP >20 mg/L are the commonly cited thresholds. Absent that imaging and lab documentation, payers have grounds to deny or downcode the claim. For lumbar discitis with concurrent vertebral body involvement, consider whether M86.06 (osteomyelitis, lumbar region) better captures the full extent of infection, or whether both codes are warranted.

If the region extends into the lumbosacral junction, M46.47 (discitis, unspecified, lumbosacral region) is the correct alternative. For multisegment involvement spanning thoracolumbar and lumbar levels, M46.45 covers the thoracolumbar region. Never use M46.40 (discitis, unspecified site) when the lumbar region is documented — site-specific coding is always preferred. MS-DRG grouping under v43.0 lands at 551 (medical back problems with MCC) or 552 (without MCC) depending on complication and comorbidity status.

Sibling codes

Other billable codes under M46.4 (laterality / anatomic variants).

M46.42

Discitis, unspecified, cervical region

M46.47

Discitis, unspecified, lumbosacral region

M46.40

Discitis, unspecified, site unspecified

M46.41

Discitis, unspecified, occipito-atlanto-axial region

M46.49

Discitis, unspecified, multiple sites in spine

M46.48

Discitis, unspecified, sacral and sacrococcygeal region

M46.44

Discitis, unspecified, thoracic region

M46.43

Discitis, unspecified, cervicothoracic region

Frequently asked questions

Source · Generated from the editorial pipeline, verified against 7 cited references ↓

01What is the difference between M46.46 and M46.40?

M46.46 is site-specific — lumbar region documented. M46.40 is unspecified site, used only when the record provides no regional localization. Always code M46.46 when the provider names the lumbar spine.

02Should I add a causative-organism code alongside M46.46?

Yes, when the organism is identified. The M46 category carries a 'use additional code' instruction. For S. aureus, add B95.61; for other identified organisms, select the applicable B95–B98 code. If the organism is unknown, M46.46 stands alone.

03When does lumbar discitis shift to M46.47 (lumbosacral region)?

When MRI or the provider's note specifically identifies the L5–S1 disc as the involved level, use M46.47. M46.46 covers L1–L5 disc spaces. If the report spans both zones, code the primary level documented by the provider.

04Can M46.46 and M86.06 (lumbar osteomyelitis) be coded together?

Yes, if the clinical record supports both disc space infection and vertebral body involvement. Discitis and vertebral osteomyelitis are distinct processes that can coexist; dual coding is appropriate when both are documented and confirmed on imaging.

05What MS-DRG does M46.46 map to?

Under MS-DRG v43.0, M46.46 groups to DRG 551 (Medical Back Problems with MCC) or DRG 552 (without MCC), depending on the presence of major complicating or comorbid conditions documented in the encounter.

06Is M46.46 appropriate for degenerative disc disease with Modic changes?

No. M46.46 requires confirmed disc space infection or inflammation — not degenerative endplate changes (Modic type I/II). Degenerative disc disease codes to M51.16 (lumbar region) or adjacent codes in the M51 category.

07What imaging is required to support M46.46?

MRI is the primary validation tool: T2 hyperintensity within the disc and endplate erosion are the key findings. X-ray alone is insufficient for early discitis. Pairing MRI findings with elevated ESR and CRP values strengthens medical necessity documentation.

Sources & references

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

Mira AI Scribe

Mira's AI scribe captures the anatomic level (L1–L5 vs. lumbosacral), MRI findings (T2 disc hyperintensity, endplate erosion), inflammatory marker values (ESR, CRP), and any identified organism from culture or biopsy — the four pillars that convert a vague 'back infection' note into defensible M46.46 documentation. Without those elements, the claim risks denial for lack of medical necessity or downcoding to unspecified site (M46.40).

See how Mira captures M46.46 documentation