ICD-10-CM · Other

M60.18

M60.18 classifies interstitial myositis occurring at a body site not captured by any other specific subcategory under M60.1 — meaning not the shoulder, upper arm, forearm, hand, thigh, lower leg, or ankle/foot.

Verified May 8, 2026 · 4 sources ↓

Status: Billable
Chapter: 13
Related CPT: 6
Region: Other

Drawn from CDCicd10data.com 2026AAPCCMS

Documentation tips

What should appear in the chart to support M60.18.

Source · Editorial brief grounded in 4 cited references ↓

Provider must name the specific anatomical site (e.g., paraspinal, intercostal, pelvic girdle) and confirm it is not one of the M60.1 subcategory sites (shoulder through ankle/foot).
Document the nature of the inflammation as interstitial/fibrotic — not infective, not granulomatous — to differentiate from M60.0x and M60.2x subcategories.
If imaging (MRI) is obtained, capture signal characteristics consistent with fibrotic or inflammatory infiltration of muscle interstitium to support medical necessity.
Record whether IBM (inclusion body myositis) was ruled out; IBM must be coded G72.41, not M60.18, per the Excludes2 note at the M60 category level.
If multiple sites are involved, evaluate M60.19 (interstitial myositis, multiple sites) before defaulting to M60.18.

Related CPT procedures

Procedure codes commonly billed with M60.18. Linking the right diagnosis to the right procedure is what establishes medical necessity.

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

20200 $241.82

Surgical removal of a tissue sample from a superficial muscle — tissue located just below the skin surface or just beneath the muscle fascia — for diagnostic laboratory analysis.

20205 $338.69

Surgical biopsy of deep muscle tissue located below the fascia or beneath adjacent muscles or bone structures.

20206 $209.76

Percutaneous needle biopsy of muscle tissue obtained without open incision, used to sample suspected pathology for diagnostic analysis.

73221 $205.08

MRI of any upper extremity joint — shoulder, elbow, or wrist — performed without contrast material.

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.

97530 View procedure details

Common coding pitfalls

The recurring mistakes coders make with M60.18 and adjacent codes.

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

Using M60.18 for inclusion body myositis — IBM is explicitly excluded from M60 via an Excludes2 note and must be coded G72.41.
Assigning M60.18 when the affected site actually maps to a specific M60.1x subcategory (e.g., coding paraspinal myositis as M60.18 is appropriate, but lower leg myositis must go to M60.16x, not M60.18).
Confusing interstitial myositis with infective myositis — infective cases require M60.0x; documentation must reflect the non-infective, fibrotic nature to support M60.18.
Defaulting to M60.18 when multiple sites are involved — M60.19 exists specifically for multi-site interstitial myositis and should be evaluated first in those scenarios.

Clinical context

Source · Editorial summary grounded in 4 cited references ↓

Interstitial myositis (M60.1x) is a non-infective inflammatory condition characterized by fibrous tissue proliferation within muscle, distinguishable from infective myositis (M60.0x) and foreign body granuloma (M60.2). M60.18 is the residual 'other site' subcategory — use it only when the affected muscle group falls outside every named anatomical subcategory in the M60.1 series. Clinically applicable sites might include the trunk musculature (paraspinal, abdominal, intercostal, pelvic girdle) or head/neck muscles not captured elsewhere in the hierarchy.

Before assigning M60.18, confirm the documentation specifies interstitial (fibrotic/infiltrative) rather than infective inflammation, and that the affected site genuinely has no more specific code. Check the Excludes2 note at M60: inclusion body myositis [IBM] maps to G72.41, not to any M60 code — do not use M60.18 as a stand-in for IBM.

For orthopedic coders, M60.18 surfaces most often in complex soft-tissue or spine cases where paraspinal or trunk muscle fibrosis is documented as a secondary or comorbid finding. Confirm the diagnosing provider explicitly names interstitial myositis; vague terms like 'muscle inflammation' or 'myalgia' do not support this code.

Sibling codes

Other billable codes under M60.1 (laterality / anatomic variants).

M60.10

Interstitial myositis of unspecified site

M60.19

Interstitial myositis, multiple sites

Frequently asked questions

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

01What sites qualify for M60.18 versus other M60.1x codes?

M60.18 applies to sites not listed in M60.10–M60.17 or M60.19. Named subcategories cover shoulder, upper arm, forearm, hand, thigh, lower leg, and ankle/foot. Trunk, paraspinal, pelvic girdle, intercostal, and head/neck muscles fall under M60.18 when only one site is affected.

02Can M60.18 and G72.41 be coded together on the same claim?

No. The Excludes2 note at M60 means a patient can theoretically have both conditions, but IBM (G72.41) is a distinct diagnosis requiring its own workup. If IBM is confirmed, use G72.41 — not M60.18. If IBM is ruled out and a separate interstitial myositis at another site is documented, M60.18 stands alone.

03When should M60.19 be used instead of M60.18?

Use M60.19 (interstitial myositis, multiple sites) when the provider documents interstitial myositis affecting two or more anatomical sites. M60.18 is reserved for a single site that is not one of the named subcategory locations.

04Does M60.18 require a 7th character?

No. M60.18 is a 5-character billable code under Chapter 13 (M-codes). The 7th-character extension convention (A/D/S) applies to injury codes (S-codes), not to musculoskeletal disease codes like M60.18.

05What documentation distinguishes M60.18 from M60.08 (infective myositis, other site)?

M60.08 requires evidence of infection — bacterial, viral, or parasitic — as the cause of muscle inflammation. M60.18 is non-infective and fibrotic in nature. The provider's clinical documentation or pathology/biopsy result must clearly indicate which type is present; absent specificity, query the provider before assigning either code.

06Is M60.18 valid for FY2026 claims?

Yes. M60.18 is a billable, valid code in the FY2026 ICD-10-CM Tabular List (effective October 1, 2025), confirmed in the CDC ICD-10-CM Tabular List 2026.

Sources & references

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

01CDC ICD-10-CM Tabular List 2026 — https://www.cdc.gov/nchs/icd/icd10cm.htm
02icd10data.com 2026 ICD-10-CM M60.18 — https://www.icd10data.com/ICD10CM/Codes/M00-M99/M60-M63/M60-/M60.18
03AAPC Codify M60.18 — https://www.aapc.com/codes/icd-10-codes/M60.18
04CMS ICD-10 Coding Resources — https://www.cms.gov/medicare/coding-billing/icd-10-codes

Mira AI Scribe

Mira AI Scribe captures the anatomical site of muscle involvement (named explicitly, outside the standard limb subcategories), the inflammatory character described as fibrotic or interstitial rather than infective, any MRI or biopsy findings supporting interstitial inflammation, and the provider's statement ruling out inclusion body myositis. This prevents downcoding to a nonspecific myositis code and blocks inadvertent use of G72.41 for a non-IBM case.

See how Mira captures M60.18 documentation