2026 ICD-10-CM Diagnosis Code M31.5Giant cell arteritis with polymyalgia rheumatica
ICD-10-CM Codes›M00–M99›M30-M36›M31
- Billable — Valid for Submission
- Risk Adjusts — HCC 94
- Chronic Condition
M31.5 is a billable ICD-10-CM diagnosis code for giant cell arteritis with polymyalgia rheumatica. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 545 through 547. Coders also document this condition as giant cell arteritis. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Systemic lupus erythematosus and connective tissue disorders and Vasculitis.
For Medicare Advantage risk adjustment, M31.5 maps to CMS-HCC Category 94 (Systemic Lupus Erythematosus and Other Specified Systemic Connective Tissue Disorders) under the V28 model, adding a risk factor of about 0.268 for a community, non-dual, aged beneficiary in payment year 2026.
Code Identity
Code Classification
Medicare Risk Adjustment (HCC)Billing
M31.5 maps to a payment category in the CMS-HCC model used to risk-adjust Medicare Advantage payments. Weights are the published community factors for payment year 2026.
Source: CMS Payment Year 2026 risk adjustment mappings and model software. Weights are relative factors, not dollar amounts; a beneficiary's total RAF also includes demographics and interactions. Browse all CMS-HCC categories.
Approximate SynonymsGuidance
Alternate terms and clinical phrases that map to this code.
- Giant cell arteritis
- Giant cell arteritis with polymyalgia rheumatica
- Polymyalgia rheumatica
Index to Diseases and InjuriesGuidance
Alphabetical index entries that point to this code.
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
Clinical InformationClinical
Giant Cell Arteritis
a systemic autoimmune disorder that typically affects medium and large arteries, usually leading to occlusive granulomatous vasculitis with transmural infiltrate containing multinucleated giant cells. the temporal artery is commonly involved. this disorder appears primarily in people over the age of 50. symptoms include fever; fatigue; headache; visual impairment; pain in the jaw and tongue; and aggravation of pain by cold temperatures. (from adams et al., principles of neurology, 6th ed)Polymyalgia Rheumatica
a syndrome in the elderly characterized by proximal joint and muscle pain, high erythrocyte sedimentation rate, and a self-limiting course. pain is usually accompanied by evidence of an inflammatory reaction. women are affected twice as commonly as men and caucasians more frequently than other groups. the condition is frequently associated with giant cell arteritis and some theories pose the possibility that the two diseases arise from a single etiology or even that they are the same entity.
Patient EducationClinical
Giant Cell Arteritis
Giant cell arteritis is a disorder that causes inflammation of your arteries, usually in the scalp, neck, and arms. It narrows the arteries, which keeps blood from flowing well. Giant cell arteritis often occurs with another disorder called polymyalgia rheumatica. Both are more common in women than in men.
Read the full article at MedlinePlus
Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.
Convert M31.5 to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About M31.5Overview
What is the ICD-10 code for giant cell arteritis with polymyalgia rheumatica?
The ICD-10-CM code for giant cell arteritis with polymyalgia rheumatica is M31.5 (sometimes written as M315). It is billable on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
Is M31.5 (Other necrotizing vasculopathies) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report giant cell arteritis with polymyalgia rheumatica on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
What MS-DRG does M31.5 group to?
When giant cell arteritis with polymyalgia rheumatica is the principal diagnosis on an inpatient stay, it groups to MS-DRG 545, 546, 547, with relative weights from 0.8362 to 2.4817 depending on complications. Higher weights mean higher Medicare reimbursement.
What is the ICD-9 equivalent of M31.5?
Under the General Equivalence Mappings, giant cell arteritis with polymyalgia rheumatica converts to ICD-9-CM 446.5 (giant cell arteritis). The mapping is approximate, so confirm the match fits the documentation.
What HCC is M31.5?
M31.5 (giant cell arteritis with polymyalgia rheumatica) maps to CMS-HCC Category 94 (Systemic Lupus Erythematosus and Other Specified Systemic Connective Tissue Disorders), commonly written as HCC 94, in the CMS-HCC V28 model used for Medicare Advantage risk adjustment in payment year 2026. It mapped to HCC 40 under the retired V24 model. It also maps in the PACE (CMS-HCC V22), ESRD (V21), and ESRD (V24) models. In the Part D prescription drug model it maps to RxHCC 84.
Does M31.5 risk-adjust for Medicare Advantage payment?
Yes. When documented and reported on a Medicare Advantage encounter, M31.5 adds a risk adjustment factor of about 0.268 to the beneficiary's RAF score for a community, non-dual, aged enrollee (published V28 weights range from 0.196 to 0.297 depending on the payment segment). A more severe related category (HCC 93) supersedes it when both are reported. See the full factor table on the HCC 94 category page.
