M46.04 identifies pathological changes at the tendon and ligament insertion sites along the thoracic spine (T1–T12), classified under other inflammatory spondylopathies.
Verified May 8, 2026 · 5 sources ↓
- Status
- Billable
- Chapter
- 13
- Related CPT
- 10
- Region
- Spine
Documentation tips
What should appear in the chart to support M46.04.
Source · Editorial brief grounded in 5 cited references ↓
- Specify 'thoracic region' or individual thoracic levels (e.g., T4–T6) in the assessment — vague 'back pain' won't support M46.04 on audit.
- Document whether the enthesopathy is inflammatory in etiology (e.g., associated with ankylosing spondylitis, psoriatic arthritis) or mechanical, as this guides medical necessity for imaging and biologics.
- Record imaging findings that support entheseal involvement: bone marrow edema at attachment sites on MRI, erosions, or new bone formation on CT or plain film.
- Note functional limitations and any conservative care already attempted (NSAIDs, PT, injections) when requesting advanced imaging or procedural authorization.
- If systemic inflammatory disease is the underlying cause, code that condition first and list M46.04 as an additional code to reflect the spinal manifestation.
Related CPT procedures
Procedure codes commonly billed with M46.04. 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 M46.04 and adjacent codes.
Source · Editorial brief grounded in CDC ICD-10-CM tabular guidance, AAOS coding references, and cited references ↓
- Using M46.00 (site unspecified) when the provider clearly documents thoracic involvement — always code to the highest specificity available.
- Selecting M46.04 for thoracolumbar junction pathology; the junction has its own code, M46.05, and mixing them creates audit exposure.
- Stacking M46.04 with M46.05 when a single enthesopathy spans both regions — use M46.09 (multiple sites) instead.
- Confusing spinal enthesopathy with peripheral enthesopathy; M46.04 is spine-only. Plantar fasciitis, epicondylitis, and similar conditions map to completely different code families.
- Failing to code the underlying spondyloarthropathy (e.g., M45.x for ankylosing spondylitis) when M46.04 represents a spinal manifestation of that systemic condition.
Clinical context
Source · Editorial summary grounded in 5 cited references ↓
Use M46.04 when the documented diagnosis is spinal enthesopathy specifically localized to the thoracic region. Enthesopathy refers to disease at the enthesis — the point where tendons, ligaments, or joint capsules attach to bone. In the thoracic spine, this manifests as pain, stiffness, or instability at costovertebral or intervertebral attachment sites, often driven by inflammatory conditions (e.g., seronegative spondyloarthropathy) or chronic mechanical overload.
M46.04 sits under parent code M46.0 (Spinal enthesopathy), which requires a 5th character for anatomic region. If the enthesopathy spans both thoracic and lumbar levels, consider M46.09 (multiple sites in spine) instead of stacking region-specific codes. If the thoracolumbar junction is the primary site, M46.05 is the correct pick. Do not use M46.04 for peripheral enthesopathy (e.g., Achilles or patellar tendon insertion) — those map to M77.x or site-specific enthesopathy codes.
MS-DRG v43.0 groups M46.04 into DRG 551 (Medical back problems with MCC) or DRG 552 (Medical back problems without MCC), making thorough comorbidity documentation directly relevant to reimbursement weight.
Sibling codes
Other billable codes under M46.0 (laterality / anatomic variants).
Frequently asked questions
Source · Generated from the editorial pipeline, verified against 5 cited references ↓
01What is the difference between M46.04 and M46.05?
02Can M46.04 be used as a primary diagnosis on a claim?
03Should I code M46.04 alongside an ankylosing spondylitis code?
04Which DRGs does M46.04 map to?
05Is M46.04 appropriate when the patient has thoracic back pain but no confirmed imaging findings yet?
06Can M46.04 and M54.6 (thoracic spine pain) be billed together?
07Does M46.04 require a 7th character?
Sources & references
Editorial content was developed using the following public sources. Last verified May 8, 2026.
- 01CDC ICD-10-CM Tabular List 2026
- 02icd10data.comhttps://www.icd10data.com/ICD10CM/Codes/M00-M99/M45-M49/M46-/M46.04
- 03aapc.comhttps://www.aapc.com/codes/icd-10-codes/M46.04
- 04unboundmedicine.comhttps://www.unboundmedicine.com/icd/view/ICD-10-CM/930206/all/M46_04___Spinal_enthesopathy__thoracic_region
- 05CMS MS-DRG v43.0 Grouper
Mira AI Scribe
Mira AI Scribe captures the anatomic level (thoracic spine, specific vertebral levels when documented), the clinical characterization of entheseal involvement (inflammatory vs. mechanical), relevant imaging findings (MRI bone marrow edema, erosions, enthesophytes), and any prior treatment tried — preventing a downcode to M46.00 (unspecified site) and supporting medical necessity for advanced imaging or injection authorization.
See how Mira captures M46.04 documentation