ICD-10-CM · Spine

M46.85

M46.85 identifies inflammatory spondylopathies of the thoracolumbar region — specifically the T12–L1 junction — that are classified as 'other specified,' meaning the condition is documented and defined but doesn't fit a more precise M46 subcategory such as ankylosing spondylitis or discitis.

Verified May 8, 2026 · 4 sources ↓

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

Drawn from CDCICD10DataAAPCCMS

Documentation tips

What should appear in the chart to support M46.85.

Source · Editorial brief grounded in 4 cited references ↓

Specify 'thoracolumbar' or 'T12-L1' region explicitly in the assessment — 'lumbar' or 'thoracic' alone will push the code to M46.86 or M46.84 respectively.
Record the imaging modality and relevant findings that support an inflammatory etiology (e.g., MRI bone marrow edema, erosive endplate changes, sacroiliac joint involvement on STIR sequence).
Document the specific type of inflammatory spondylopathy when known (e.g., psoriatic, reactive, enteropathic) so auditors can confirm 'other specified' rather than 'unspecified' is correct; if truly unspecified, M46.90 is the appropriate fallback.
Note any elevated inflammatory markers (CRP, ESR, HLA-B27 status) in the clinical note — these support medical necessity and distinguish inflammatory from mechanical back conditions.
If the patient has a known systemic inflammatory condition (e.g., IBD, psoriasis), code the underlying condition additionally, as it corroborates the inflammatory spondylopathy diagnosis.

Related CPT procedures

Procedure codes commonly billed with M46.85. 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.

72158 $318.31

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

72020 $23.71

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

72070 $33.07

Two-view radiologic examination of the thoracic spine, including AP and lateral projections of the 12 thoracic vertebrae.

72100 $40.42

Radiologic examination of the lumbosacral spine capturing two or three views, used to evaluate the lumbar vertebrae and sacrum for injury, degeneration, or structural abnormality.

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.

20610 $68.81

Aspiration and/or injection of a major joint or bursa (shoulder, hip, knee, or subacromial bursa) performed without ultrasound guidance.

77080 View procedure details

Common coding pitfalls

The recurring mistakes coders make with M46.85 and adjacent codes.

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

Assigning M46.85 based on clinical suspicion alone without imaging or lab evidence of inflammation — payers flag this as unsupported and may deny or downcode to an unspecified or symptom code.
Confusing 'thoracolumbar' (T12–L1 junction, coded as 5th character '5') with 'thoracic' (5th character '4') or 'lumbar' (5th character '6') — these are distinct codes and the wrong one triggers a specificity mismatch on audit.
Using M46.85 when ankylosing spondylitis is the confirmed diagnosis — AS has its own code (M45.x) and M46.85 should not be used as a substitute.
Defaulting to M46.85 for any inflammatory-sounding back pain instead of querying the provider for specificity — if the condition is truly unspecified, M46.90 (unspecified inflammatory spondylopathy, site unspecified) or the appropriate site-specific unspecified code applies.

Clinical context

Source · Editorial summary grounded in 4 cited references ↓

Use M46.85 when the treating provider has documented a specific inflammatory spondylopathy affecting the thoracolumbar spine (the T12–L1 transitional zone) and the condition doesn't map to a named category elsewhere in M46. Classic examples include reactive arthritis-related spinal inflammation, psoriatic spondylopathy, or enteropathic spondylopathy localized to the thoracolumbar region — provided the physician's documentation uses inflammatory language and imaging supports an inflammatory rather than degenerative process.

Do not use M46.85 as a default for nonspecific back pain at the thoracolumbar level. Imaging must reflect an inflammatory process — bone marrow edema on MRI, erosive changes, or equivalent findings — before this code is clinically supported. If the imaging shows degenerative joint disease, osteoarthritis codes from the M47 range are more appropriate.

M46.85 maps to MS-DRG 551 (Medical back problems with MCC) or 552 (Medical back problems without MCC) under CMS v43.0, so correct assignment directly affects DRG weight and facility reimbursement. Thoracolumbar-region specificity is encoded in the 5th character (5 = thoracolumbar); adjacent codes M46.84 (thoracic) and M46.86 (lumbar) differ only in regional location, so region documentation is critical.

Sibling codes

Other billable codes under M46.8 (laterality / anatomic variants).

M46.87

Oth inflammatory spondylopathies, lumbosacral region

M46.82

Oth inflammatory spondylopathies, cervical region

M46.83

Oth inflammatory spondylopathies, cervicothoracic region

M46.81

Oth inflammatory spondylopathies, occipt-atlan-ax region

M46.89

Oth inflammatory spondylopathies, multiple sites in spine

M46.88

Oth inflammatory spondylopathies, sacr/sacrocygl region

M46.84

Oth inflammatory spondylopathies, thoracic region

M46.86

Other specified inflammatory spondylopathies, lumbar region

Frequently asked questions

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

01What makes a spondylopathy 'other specified' versus 'unspecified' for M46.85?

'Other specified' means the provider has identified and documented a defined type of inflammatory spondylopathy (e.g., reactive, psoriatic, enteropathic) that doesn't have its own dedicated ICD-10-CM code. 'Unspecified' (M46.90–M46.99) applies when the documentation doesn't name a specific condition. If the chart says only 'inflammatory back pain,' query the provider before using M46.85.

02Can M46.85 be used alongside a code for ankylosing spondylitis?

No. Ankylosing spondylitis is classified under M45.x, which excludes other inflammatory spondylopathies in the same coding session for the same condition. Use M45.x when AS is the confirmed diagnosis.

03What DRGs does M46.85 map to?

Under MS-DRG v43.0, M46.85 groups to DRG 551 (Medical back problems with MCC) or DRG 552 (Medical back problems without MCC), depending on the presence of a major complication or comorbidity.

04Is imaging required to support M46.85?

Imaging supporting an inflammatory process — MRI bone marrow edema, erosive endplate changes, or equivalent findings — is the standard of clinical and coding support. Without it, the diagnosis is difficult to defend on audit and payers may deny medical necessity. Lab markers (CRP, ESR, HLA-B27) further corroborate the diagnosis.

05How does M46.85 differ from M46.84 and M46.86?

All three fall under M46.8 (other specified inflammatory spondylopathies) and differ only by spinal region: M46.84 = thoracic, M46.85 = thoracolumbar (T12–L1), M46.86 = lumbar. The provider must document the affected region by name or anatomic level for the correct 5th-character assignment.

06Can M46.85 be a primary diagnosis on an orthopedic claim?

Yes, M46.85 is a fully billable, specific ICD-10-CM code and can stand as the primary diagnosis when the encounter is driven by the management of the inflammatory spondylopathy at the thoracolumbar region.

07Should a secondary code be added for a systemic condition driving the spinal inflammation?

Yes. If a systemic condition — such as Crohn's disease, ulcerative colitis, or psoriasis — is the underlying cause of the spondylopathy, code the systemic condition additionally. Sequencing depends on which condition is the reason for the encounter.

Sources & references

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

01CDC ICD-10-CM Tabular List 2026
02
icd10data.com
https://www.icd10data.com/ICD10CM/Codes/M00-M99/M45-M49/M46-/M46.85
03
aapc.com
https://www.aapc.com/codes/icd-10-codes/M46.85
04CMS MS-DRG v43.0 Grouper Documentation

Mira AI Scribe

Mira's AI scribe captures the specific spinal region (thoracolumbar/T12–L1), the imaging findings confirming inflammation (MRI edema pattern, erosions, Kellgren grade if applicable), any associated systemic inflammatory condition, and the provider's explicit characterization of the spondylopathy type. This prevents downcoding to an unspecified spondylopathy code and supports the 'other specified' designation required to bill M46.85 without an audit flag.

See how Mira captures M46.85 documentation