2026 ICD-10-CM Diagnosis Code M46.91Unspecified inflammatory spondylopathy, occipito-atlanto-axial region
ICD-10-CM Codes›M00–M99›M45-M49›M46
- Billable — Valid for Submission
- Not Chronic
M46.91 is a billable ICD-10-CM diagnosis code for unspecified inflammatory spondylopathy, occipito-atlanto-axial region. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 551 through 552. Coders also document this condition as axial spondyloarthritis. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Spondylopathies/spondyloarthropathy (including infective).
M46.91 no longer risk-adjusts for Medicare Advantage: it mapped to HCC 40 under the retired CMS-HCC V24 model through payment year 2025 but maps to no category in the live V28 model. It still risk-adjusts in the PACE (CMS-HCC V22) category 40, ESRD (V21) category 40, and ESRD (V24) category 40 for payment year 2026.
Code Identity
Code Classification
Medicare Risk Adjustment (HCC)Billing
M46.91 no longer risk-adjusts for Medicare Advantage: it maps to no payment category in the live CMS-HCC V28 model, although it still risk-adjusts in the other CMS models shown below.
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.
- Axial spondyloarthritis
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
Axial Spondyloarthritis
a spectrum of chronic inflammatory conditions affecting the axial joints (e.g., spine), characterized by pain, stiffness of joints (ankylosis), reduced mobility and inflammation. when joint inflammation and damage are visible on regular x-rays it is called ankylosing spondylitis; otherwise it is referred to as non-radiographic axial spondyloarthritis. hla-b27 antigen is a biomarker and il-23/il-17 pathway a potential therapeutic target for axial and other related spondyloarthritis.Non-Radiographic Axial Spondyloarthritis
chronic inflammatory conditions affecting the axial joints which cannot be detectable on x-rays. it is characterized by pain, stiffness of joints and inflammation. non-radiographic axial spondyloarthritis can have symptoms onset before the age of 45 and progress to more severe ankylosing spondylitis over time.
Patient EducationClinical
Spine Injuries and Disorders
Your backbone, or spine, is made up of 26 bone discs called vertebrae. The vertebrae protect your spinal cord and allow you to stand and bend. A number of problems can change the structure of the spine or damage the vertebrae and surrounding tissue. They include:
Read the full article at MedlinePlus
Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.
Convert M46.91 to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About M46.91Overview
What is the ICD-10 code for unspecified inflammatory spondylopathy, occipito-atlanto-axial region?
The ICD-10-CM code for unspecified inflammatory spondylopathy, occipito-atlanto-axial region is M46.91 (sometimes written as M4691). It is billable on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
Is M46.91 (Unspecified inflammatory spondylopathy) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report unspecified inflammatory spondylopathy, occipito-atlanto-axial region on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
What MS-DRG does M46.91 group to?
When unspecified inflammatory spondylopathy, occipito-atlanto-axial region is the principal diagnosis on an inpatient stay, it groups to MS-DRG 551, 552, with relative weights from 0.9613 to 1.6761 depending on complications. Higher weights mean higher Medicare reimbursement.
What is the ICD-9 equivalent of M46.91?
Under the General Equivalence Mappings, unspecified inflammatory spondylopathy, occipito-atlanto-axial region converts to ICD-9-CM 720.9 (inflam spondylopathy NOS). The mapping is approximate, so confirm the match fits the documentation.
Does M46.91 risk-adjust for Medicare Advantage payment?
Not for Medicare Advantage. M46.91 mapped to HCC 40 in the retired CMS-HCC V24 model, which last determined payment in 2025, but it maps to no category in the live V28 model; see all codes that no longer risk-adjust. It still risk-adjusts in the PACE (CMS-HCC V22) category 40 (Rheumatoid Arthritis and Inflammatory Connective Tissue Disease), ESRD (V21) category 40 (Rheumatoid Arthritis and Inflammatory Connective Tissue Disease), and ESRD (V24) category 40 (Rheumatoid Arthritis and Inflammatory Connective Tissue Disease).
