On October 1, 2025, International Classification of Diseases, Tenth Revision, Clinical Modification (ICD-10-CM) updates took effect, introducing major changes to multiple sclerosis ICD-10 coding. The single multiple sclerosis (MS) code, G35, used since ICD-10-CM was implemented in 2015, expanded into subcategories that capture disease course: relapsing-remitting (G35.A), primary progressive (G35.B), secondary progressive (G35.C), and unspecified (G35.D), with active and non-active codes for the progressive forms.
MS is a chronic, progressive neurological disease in which the immune system attacks the protective sheath covering nerve fibers (known as myelin), disrupting communication between the brain and the rest of the body. It affects nearly 1 million people in the United States, according to the Multiple Sclerosis Association of America, and is one of the most commonly known neurological conditions.
Before this update, ICD-10-CM coding for MS lacked the specificity needed to capture disease severity, activity, and treatment decisions. This gap created challenges for documentation, risk adjustment, and reimbursement. The 2025 update marks a milestone, bringing coding into alignment with clinical practice and integrated patient care.
Article Highlights
Beginning October 1, 2025, the MS code category expanded from a single code (G35) into detailed subcategories, allowing clinicians and coders to capture disease course with greater precision.
- The subcategories are G35.A (relapsing-remitting), G35.B (primary progressive), G35.C (secondary progressive), and G35.D (unspecified), with unspecified, active, and non-active codes under G35.B and G35.C.
- Active MS refers to clinical relapses, new MRI activity, or disease progression requiring therapeutic intervention; non-active MS refers to disease stability without recent relapse or imaging changes.
- Cognitive impairment and mental health challenges are common among patients with MS, affecting up to 65% of patients according to Cleveland Clinic, and estimates suggest cognitive dysfunction affects 40–70% of people with MS, even at the time of diagnosis.
For clinicians, coders, and revenue cycle teams, these updates are more than just a coding change; they reflect evolving clinical understanding and the critical role of integrated neurology and behavioral health management.
Understanding multiple sclerosis and its impact
Symptoms of MS vary widely but often include fatigue, numbness, muscle weakness, vision problems, and mobility challenges.
Beyond the physiological symptoms, cognitive impairment and mental health challenges are common among patients with MS, affecting up to 65% of patients, according to Cleveland Clinic. Memory loss, slowed processing speed, difficulty concentrating, and depression resulting from MS can significantly reduce quality of life. Without structured assessment, cognitive and mood changes may be overlooked, limiting early interventions and leaving documentation and risk-adjusted reimbursement incomplete.
Given its complexity, MS is increasingly recognized not just as a physical disease but as one requiring integrated neurological and behavioral health management. Accurate coding reflecting both disease activity and cognitive impact is essential, not only for patient care but for ensuring documentation supports proper reimbursement, care coordination, and quality reporting.
What are the new multiple sclerosis ICD-10-CM codes?
The 2025 ICD-10-CM update introduces major revisions to MS coding, representing one of the most significant expansions in recent years.
Since ICD-10-CM was implemented in 2015, MS has been captured by a single code (G35) with no further distinctions. Beginning October 1, 2025, the MS code category expanded into detailed subcategories, allowing clinicians and coders to capture disease course with greater precision:
| Subcategory | Disease course | Codes |
|---|---|---|
| G35.A | Relapsing-remitting multiple sclerosis | G35.A |
| G35.B | Primary progressive multiple sclerosis | G35.B0: unspecified G35.B1: active G35.B2: non-active |
| G35.C | Secondary progressive multiple sclerosis | G35.C0: unspecified G35.C1: active G35.C2: non-active |
| G35.D | Multiple sclerosis, unspecified (retains prior generalized terms) | G35.D |
Defining active vs. non-active MS
- Active MS refers to clinical relapses, new MRI activity, or disease progression requiring therapeutic intervention.
- Non-active MS refers to disease stability without recent relapse or imaging changes.
These refinements enable more precise documentation of disease trajectory and treatment response, supporting care planning, quality reporting, and reimbursement integrity.
Why do the new MS codes matter?
Coding specificity is more than just an administrative detail; it directly impacts patient care, reporting accuracy, and reimbursement.
Key benefits of MS coding specificity
- Documentation accuracy: differentiates relapsing vs. progressive MS and active vs. non-active states.
- Clinical alignment: reflects real-world treatment decisions.
- Quality programs: supports Merit-based Incentive Payment System (MIPS) reporting, care coordination, and population health tracking.
- Reimbursement integrity: MS codes now carry Hierarchical Condition Category (HCC) risk adjustment value, affecting risk adjustment factor (RAF) scores and funding. Previously, a lack of specificity left room for undercoding and underpayment.
- Research and data: generates richer datasets that capture the full spectrum of MS clinical presentations.
Case example: coding MS progression
Consider a patient initially diagnosed with relapsing-remitting MS (G35.A). Years later, they transition to secondary progressive MS, active (G35.C1). Previously, both stages would have been coded simply as G35, masking disease progression and potentially affecting treatment decisions and reimbursement. With the updated codes, the disease trajectory is captured accurately, ensuring alignment across clinical care, research, and funding.
How does MS affect cognition and mental health?
MS affects more than mobility and motor function. Cognitive changes and comorbid mood disorders may appear early (sometimes even before physical decline) and can progress silently. Without structured assessment, these symptoms may go undetected, delaying tailored support and targeted interventions, resulting in incomplete documentation and missed reimbursement opportunities tied to risk adjustment.
Evidence highlights the value of early cognitive testing in MS
- Early impairment as a predictor of disease progression: cognitive deficits can emerge in early or even asymptomatic stages of MS, which in some cases may serve as a predictor of disease progression, prompting early rehabilitation efforts.
- Routine monitoring for informing intervention and assessing treatment effectiveness: Ongoing cognitive assessment may reveal disease activity, cognitive impacts of comorbid mood disorders, or medication effects, helping identify patients who could benefit from intervention.
- High prevalence of cognitive impairment at diagnosis: estimates published in Multiple Sclerosis and Related Disorders suggest cognitive dysfunction affects 40–70% of people with MS, even at the time of diagnosis, emphasizing the need for routine screening with validated tests like the Symbol Digit Modalities Test (SDMT).
Early detection can change care trajectories. Identifying slowed processing, memory lapses, or diminished concentration early allows clinicians to deliver tailored, adaptive treatment plans for an often-overlooked aspect of MS care.
The role of digital tools like Creyos in MS care
When integrated early in the care workflow, Creyos enables neurology and behavioral health teams to provide:
- Objective, validated assessment of key cognitive domains such as processing speed, reasoning ability, memory, and attention.
- Longitudinal tracking to detect subtle changes over time and prompt timely intervention.
- Actionable insights that support adaptive care planning and strengthen documentation for both clinical and reimbursement purposes.
By uncovering and monitoring cognitive changes that often go unnoticed, Creyos helps care teams intervene sooner and more precisely, while ensuring coding accurately reflects patient complexity and supports reimbursement.
Preparing for the MS coding updates effective October 1, 2025
To ensure readiness, clinicians and coders should:
- Review the updated MS codes and adjust documentation practices accordingly.
- Educate care teams (from neurologists to behavioral health clinicians) on capturing both physical and cognitive dimensions of MS.
- Integrate supportive tools like Creyos to strengthen assessment, documentation, and compliance.
Key takeaway for MS coding and care
The October 2025 multiple sclerosis ICD-10-CM updates reflect the growing recognition that MS impacts both physical and cognitive health. More precise coding, combined with structured cognitive and behavioral health assessments, enables clinicians to deliver better-informed care while safeguarding reimbursement integrity.
The dual benefit is clear:
- Clinical: enables more precise, tailored care strategies that improve patient outcomes.
- Financial: strengthens revenue integrity through accurate coding and compliance.
With tools like Creyos, clinicians can confidently implement these changes, ensuring patients with MS receive proactive, coordinated care while documentation and coding fully reflect their complexity.
Written by Emily Montemayor, Medical Coding Support Manager at Creyos
Emily Montemayor, a CCS, COC, CPC, CPMA, CMBCS, QMRAC, CPC-I, CPA-EDU Approved Instructor, is a recognized expert in coding compliance, revenue integrity, and provider education. As Medical Coding Support Manager at Creyos and Director of Education for OAHIMA, she has led international training and initiatives that optimize reimbursement, enhance documentation, and advance coding practices, driven by her passion for empowering healthcare teams and improving patient care through education and compliance excellence.