What is ICD-10 code M31.5?

M31.5 is the ICD-10-CM diagnosis code for Giant cell arteritis with polymyalgia rheumatica. A condition where large arteries become inflamed (giant cell arteritis) and is accompanied by muscle pain and stiffness, particularly in the shoulders and hips (polymyalgia rheumatica). M31.5 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. M31.5 is part of the FY2026 ICD-10-CM code set published by the CMS National Center for Health Statistics and used on Medicare, Medicaid, and commercial claims in the United States.

Yes. M31.5 is a billable ICD-10-CM code that can be reported on professional and institutional claims as a primary or secondary diagnosis when the provider documentation supports the specific condition described. Billable codes in ICD-10-CM are coded to the highest level of specificity available for the documented diagnosis. M31.5 is current for fiscal year 2026 and remains in the active CMS ICD-10-CM code set published by the National Center for Health Statistics.

What should coders know when reporting M31.5?

Code both the giant cell arteritis and polymyalgia rheumatica components Document any vision complications or temporal artery involvement Because M31.5 maps to a payment HCC, the documentation must also satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's risk adjustment score.

2026 ICD-10-CM M31.5: Giant cell arteritis

ICD-10-CM Code View

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Code lookupM31.5Effective periodFY2026 Apr Update (Apr 1-Sep 30)

FY 2026 Apr update / Diseases of the musculoskeletal system and connective tissue (M00-M99) / Systemic connective tissue disorders (M30-M36)

M31.5

Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidance

Giant cell arteritis with polymyalgia rheumatica

A condition where large arteries become inflamed (giant cell arteritis) and is accompanied by muscle pain and stiffness, particularly in the shoulders and hips (polymyalgia rheumatica).

Buddy Insight

Giant cell arteritis with polymyalgia rheumatica represents a combination of large vessel vasculitis with associated muscle pain and stiffness, typically affecting patients over 50 years.

CMS-HCC V28

Mapped

HCC 94

Systemic Lupus Erythematosus ...

RAF 0.268

CMS-HCC V24

Mapped

HCC 40

Rheumatoid Arthritis and Infl...

RAF 0.421

ACA/HHS

Mapped

HCC 57

HHS-HCC 57

Varies by metal level

ESRD/PACE

Mapped

HCC 40

Rheumatoid Arthritis and Infl...

RAF 0.058

RXHCC

Mapped

HCC 84

Vasculitis and Other Autoimmu...

RAF 0.113

Code Book Path

Official

M31Other necrotizing vasculopathies

M31.5Giant cell arteritis with polymyalgia rheumatica

Inclusion Terms

Official

ICD-10-CM does not list inclusion terms for M31.5 in this effective period.

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for M31.5 in this effective period.

Related Child Codes

Official

M31.0Hypersensitivity angiitis

M31.1Thrombotic microangiopathy

M31.2Lethal midline granuloma

M31.3Wegener's granulomatosis

M31.4Aortic arch syndrome [Takayasu]

Includes

Official

ICD-10-CM does not list Includes notes for M31.5 in this effective period.

Excludes 1

Official

ICD-10-CM does not list Excludes 1 notes for M31.5 in this effective period.

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for M31.5 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for M31.5 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for M31.5 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance

Patient age typically over 50 years

Clinical evidence of giant cell arteritis (temporal artery involvement)

Concurrent polymyalgia rheumatica symptoms

Elevated inflammatory markers (ESR, CRP)

MEAT Support

HCC Buddy guidance

Patient age typically over 50 years

Clinical evidence of giant cell arteritis (temporal artery involvement)

Concurrent polymyalgia rheumatica symptoms

Elevated inflammatory markers (ESR, CRP)

Audit Caution

HCC Buddy guidance

Using separate codes for GCA and PMR when they coexist

Missing the combined nature of the condition

Using only headache codes for temporal symptoms

Confusing with Takayasu arteritis in younger patients

Common Mistakes

HCC Buddy guidance

M31.6 — Other giant cell arteritis (without polymyalgia rheumatica)

M35.3 — Polymyalgia rheumatica (without arteritis component)

M31.4 — Aortic arch syndrome (Takayasu arteritis)

G44.001 — Cluster headache syndrome, unspecified (headache only)

Current with CMS: FY2026 ICD-10-CM Apr 1 update (effective Apr 1 – Sep 30, 2026) · CMS-HCC V28, 100% phased in for payment year 2026. FY2027 code set already staged for October 1, 2026. How HCC Buddy stays current →

Is M31.5 an HCC code?

Yes. M31.5 (Giant cell arteritis with polymyalgia rheumatica) maps to Systemic Lupus Erythematosus and Other Specified Systemic Connective Tissue Disorders under the CMS-HCC V28 risk adjustment model (and Rheumatoid Arthritis and Inflammatory Connective Tissue Disease under V24), with a community non-dual aged RAF of 0.268. It is billable for payment year 2026.

Coder answer: M31.5 is billable and maps to V28 HCC 94, Systemic Lupus Erythematosus and Other Specified Systemic Connective Tissue Disorders. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.

Code: M31.5
Description: Giant cell arteritis with polymyalgia rheumatica
HCC (V28): HCC 94 — Systemic Lupus Erythematosus and Other Specified Systemic Connective Tissue Disorders
RAF: 0.268
Billable: Yes
Payment year: 2026

HCC Category Mapping

V28HCC 94, Systemic Lupus Erythematosus and Other Specified Systemic Connective Tissue Disorders

0.268

V24HCC 40, Rheumatoid Arthritis and Inflammatory Connective Tissue Disease

0.421

ESRDHCC 40, Rheumatoid Arthritis and Inflammatory Connective Tissue Disease

0.058

RxHCCHCC 84, Vasculitis and Other Autoimmune Disorders

0.113

Each model's RAF is its CMS base weight for that model's standard population, so weights are not directly comparable across models: CMS-HCC V28 and V24 use Community, Non-Dual, Aged; ESRD uses the dialysis continuing-enrollee model; RxHCC is the Part D continuing-enrollee, non-low-income, aged weight (a larger scale than CMS-HCC). ACA/HHS has no single weight — it varies by metal level. Actual per-patient RAF contribution depends on member segment, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains in use during the transition and for historical data.

Work M31.5 in the Code Book — tabular path, V28 RAF, and MEAT checklist →

MEAT Criteria for M31.5

For M31.5 to count as a valid HCC diagnosis in a given encounter, the provider's documentation must show MEAT: Monitor, Evaluate, Assess, or Treat. A diagnosis from a prior year does not carry forward automatically, it has to be re-documented and supported each calendar year.

MMonitor: signs, symptoms, disease progression, or lab trending documented in the note
EEvaluate: test results, medication response, or physical findings reviewed by the provider
AAssess: explicit mention in the assessment or plan with acknowledgment of status
TTreat: medication, referral, procedure, therapy, or counseling tied to the diagnosis

Only one of M/E/A/T is required to support the code, but the documentation must be specific enough to show that the provider actually addressed M31.5 during that encounter, not just copy-forwarded from a problem list.

Coder workflow notes

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What This Code Means

M31.5 is the ICD-10-CM diagnosis code for giant cell arteritis with polymyalgia rheumatica. A condition where large arteries become inflamed (giant cell arteritis) and is accompanied by muscle pain and stiffness, particularly in the shoulders and hips (polymyalgia rheumatica). M31.5 sits in the ICD-10-CM chapter for diseases of the musculoskeletal system and connective tissue (m00-m99), within the section covering systemic connective tissue disorders (m30-m36).

Under the CMS-HCC V28 risk adjustment model, M31.5 maps to Systemic Lupus Erythematosus and Other Specified Systemic Connective Tissue Disorders (HCC 94) with a community, non-dual, aged base RAF weight of 0.268. Under the older CMS-HCC V24 model, M31.5 maps to Rheumatoid Arthritis and Inflammatory Connective Tissue Disease (HCC 40) with a community, non-dual, aged base RAF weight of 0.421. V28 is the CMS-HCC risk adjustment model that reached 100% phase-in for payment year 2026, replacing V24 which was used during the PY2024–PY2025 transition.

Code both the giant cell arteritis and polymyalgia rheumatica components. Because M31.5 maps to a payment HCC, the provider's documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's Medicare Advantage risk adjustment score. When documentation is ambiguous, coders should issue a provider query rather than assume the highest-specificity variant.

HCC Buddy maintains structured V28 and V24 mapping, RAF weights, and MEAT documentation criteria for M31.5 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•Code both the giant cell arteritis and polymyalgia rheumatica components
•Document any vision complications or temporal artery involvement

Clinical Significance

Giant cell arteritis with polymyalgia rheumatica represents a combination of large vessel vasculitis with associated muscle pain and stiffness, typically affecting patients over 50 years. This condition carries risk of blindness and requires immediate high-dose corticosteroid treatment.

Documentation Requirements

✓Patient age typically over 50 years
✓Clinical evidence of giant cell arteritis (temporal artery involvement)
✓Concurrent polymyalgia rheumatica symptoms
✓Elevated inflammatory markers (ESR, CRP)
✓Temporal artery biopsy if performed
✓Assessment of visual symptoms
✓Response to corticosteroid therapy
✓Monitoring for steroid-related complications

Commonly Confused Codes

•M31.6: Other giant cell arteritis (without polymyalgia rheumatica)
•M35.3: Polymyalgia rheumatica (without arteritis component)
•M31.4: Aortic arch syndrome (Takayasu arteritis)
•G44.001: Cluster headache syndrome, unspecified (headache only)
•H34.10: Central retinal artery occlusion, unspecified eye (visual complications only)