M99.46

M99.46 identifies connective tissue stenosis of the neural canal localized to the lower extremity — a biomechanical lesion in which fibrotic or thickened connective tissue narrows the bony canal through which neural structures pass in the lower limb region.

Verified May 8, 2026 · 5 sources ↓

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

Drawn from CDCicd10data.com —AAPCPain PhysicianCMS

Documentation tips

What should appear in the chart to support M99.46.

Source · Editorial brief grounded in 5 cited references ↓

Specify the tissue type causing stenosis — document 'fibrosis,' 'ligamentous hypertrophy,' or 'connective tissue thickening' to justify M99.46 over osseous (M99.36) or disc-related (M99.56) alternatives.
Identify the anatomic segment of the lower extremity affected (hip, thigh, knee, leg, or ankle region) even though the code does not have a laterality character — this supports audit defense and clinical coherence.
Record imaging or diagnostic findings that confirm connective tissue involvement: MRI soft-tissue signal changes, ultrasound findings of fibrotic bands, or operative/pathology notes describing connective tissue proliferation.
Document the resulting neural compromise: numbness, radicular pain, neurogenic claudication, weakness, or reflex changes in the lower extremity distribution.
Note conservative treatment history (physical therapy, injections, manual therapy) when used as the primary diagnosis on claims for ongoing management — payers require evidence of active treatment rationale.

Related CPT procedures

Procedure codes commonly billed with M99.46. Linking the right diagnosis to the right procedure is what establishes medical necessity.

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

27096 $175.69

Injection into the sacroiliac joint with fluoroscopic or CT image guidance, including arthrography when performed.

27447 $1,159.35

Knee replacement surgery addressing both the medial and lateral tibiofemoral compartments, with or without resurfacing of the patella.

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.

73721 $204.41

MRI of a lower extremity joint (hip, knee, or ankle) performed without contrast material.

97110 $29.06

Therapeutic exercise billed per 15-minute unit, targeting strength, endurance, range of motion, or flexibility with direct one-on-one patient contact.

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.

64483 View procedure details

98940 View procedure details

98941 View procedure details

Common coding pitfalls

The recurring mistakes coders make with M99.46 and adjacent codes.

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

Using M99.46 interchangeably with M48.06 (spinal stenosis, lumbar region) — M99.46 is reserved for connective tissue mechanism affecting the lower extremity neural canal, not the lumbar vertebral canal itself.
Selecting M99.46 when the stenosis is driven by bony overgrowth or osteophytes — that scenario codes to M99.36 (osseous stenosis of neural canal of lower extremity), not M99.46.
Omitting a secondary symptom or functional impairment code — M99.46 alone rarely establishes medical necessity for imaging, injections, or surgical consult without a paired pain or neurological deficit code.
Confusing the M99.4x series (neural canal stenosis) with the M99.7x series (connective tissue and disc stenosis of intervertebral foramina) — foraminal stenosis has its own subcategory and should not be reported with M99.46.
Assuming M99.46 requires a 7th character — it does not. M-codes in this section are complete without 7th-character extensions.

Clinical context

Source · Editorial summary grounded in 5 cited references ↓

M99.46 falls under the M99.4x subcategory (Connective tissue stenosis of neural canal) within the broader M99 block of biomechanical lesions. Unlike M48.0x spinal stenosis codes — which describe structural narrowing of the vertebral canal — M99.46 is used when the stenosis mechanism is connective tissue proliferation or fibrosis affecting neural canal space in the lower extremity. This distinction matters at audit: payers and MACs expect the code to reflect not just location but the tissue type driving the stenosis.

This code appears most often in osteopathic, chiropractic, and physiatry billing contexts, and occasionally in orthopedic documentation when connective tissue changes (e.g., scar tissue, ligamentous hypertrophy, fibrotic bands) are identified as compressing neural canal structures in the hip, thigh, knee, or leg region. If the stenosis is osseous in origin rather than connective tissue, use M99.36 instead. If the mechanism is intervertebral disc-related, use M99.56.

M99.46 does not carry a laterality 6th character — the code is complete as a 5-character billable code designating the lower extremity as the region. When bilateral lower extremity involvement is documented, coding guidelines support reporting M99.46 once unless payer-specific policy requires separate encounter-level justification. Always pair with a symptom or functional code (e.g., radiculopathy, neurogenic claudication, lower extremity pain) to establish medical necessity.

Sibling codes

Other billable codes under M99.4 (laterality / anatomic variants).

M99.48

Connective tissue stenosis of neural canal of rib cage

M99.40

Connective tissue stenosis of neural canal of head region

M99.45

Connective tissue stenosis of neural canal of pelvic region

M99.43

Connective tissue stenosis of neural canal of lumbar region

M99.47

Connective tiss stenosis of neural canal of upper extremity

M99.42

Connective tiss stenosis of neural canal of thoracic region

M99.44

Connective tissue stenosis of neural canal of sacral region

M99.49

Conn tiss stenos of neural canal of abdomen and oth regions

Frequently asked questions

Source · Generated from the editorial pipeline, verified against 5 cited references ↓

01What distinguishes M99.46 from M48.06 (spinal stenosis, lumbar region)?

M48.06 describes structural narrowing within the lumbar vertebral canal itself, regardless of mechanism. M99.46 is a biomechanical lesion code specific to connective tissue as the stenotic mechanism, localized to the lower extremity neural canal rather than the spinal column. Use M48.06 for lumbar canal stenosis; use M99.46 when fibrotic or connective tissue changes compress neural structures in the lower limb region.

02Does M99.46 require a laterality character?

No. M99.46 is a complete 5-character billable code. The M99.4x subcategory designates region (e.g., lower extremity) rather than left-versus-right laterality, so no additional character is needed or valid.

03When should M99.36 be used instead of M99.46?

Use M99.36 (osseous stenosis of neural canal of lower extremity) when bony structures — osteophytes, hypertrophied bone, or calcified tissue — are the primary cause of neural canal narrowing. M99.46 applies only when the stenotic mechanism is connective tissue such as fibrosis, scar tissue, or ligamentous hypertrophy.

04Can M99.46 be the primary diagnosis on a chiropractic or OMT claim?

It can appear on such claims, but Medicare and many commercial payers require a segmental dysfunction code (M99.0x) as the primary diagnosis for chiropractic services, with M99.46 as a supporting secondary diagnosis. Verify payer-specific LCD requirements before listing M99.46 as the first-listed code on manual therapy claims.

05Is M99.46 appropriate for post-surgical fibrosis causing lower extremity neural compression?

Potentially yes, if the operative report or imaging confirms fibrotic connective tissue narrowing the neural canal in the lower extremity. However, if the stenosis is at the lumbar or sacral spine level as a result of scar tissue from prior back surgery, consider M96.1 (postlaminectomy syndrome) or M99.43/M99.44 (lumbar/sacral region) depending on where the connective tissue stenosis actually occurs.

06What CPT procedures are most commonly reported alongside M99.46?

Common pairings include imaging (72148 lumbar MRI, 73721 knee MRI), nerve conduction studies or EMG (not listed in CPT here), manipulation codes (98940-98941), therapeutic exercise (97110), and evaluation and management codes (99213-99214) when the condition is managed conservatively in a clinic setting.

07Is a 7th character required or permitted with M99.46?

No 7th character applies to M99.46. The 7th-character extension convention (A/D/S for initial/subsequent/sequela) is used with injury S-codes, not with M-code biomechanical lesion categories like M99.

Sources & references

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

01CDC ICD-10-CM Tabular List 2026 — https://icd10cmtool.cdc.gov/
02icd10data.com — https://www.icd10data.com/ICD10CM/Codes/M00-M99/M99-M99/M99-/M99.46
03AAPC Codify — https://www.aapc.com/codes/icd-10-codes/M99.46
04Pain Physician Journal ICD-10 comparison table — https://www.painphysicianjournal.com/current/pdf/MTUwMQ%3D%3D/63
05CMS ICD-10-CM Official Guidelines for Coding and Reporting — https://www.cms.gov/Medicare/Coding/ICD10/Downloads/2019-ICD10-Coding-Guidelines-.pdf

Mira AI Scribe

Mira's AI scribe captures the specific connective tissue mechanism (fibrosis, ligamentous thickening, fibrotic banding), the lower extremity segment involved, relevant imaging findings confirming soft-tissue neural canal compromise, and any neurological signs in the lower limb. This prevents downcoding to an unspecified stenosis code, misassignment to the osseous (M99.36) or disc (M99.56) alternatives, and denial for missing medical necessity documentation.

See how Mira captures M99.46 documentation