Starting October 1, 2025, the single diagnosis code doctors have long used for multiple sclerosis (MS)—ICD-10 code G35—will be retired. In its place, new phenotype-specific codes will describe the exact type and activity level of each person’s MS.
What Is an ICD-10 Code?
“ICD” stands for International Classification of Diseases. These are standardized numbers that doctors, hospitals, pharmacies, and insurance companies use to describe a diagnosis in electronic health records and on insurance claims.
- Think of it like a universal medical shorthand—instead of writing “relapsing-remitting multiple sclerosis,” a provider enters a code that every computer system and insurance plan recognizes.
- These codes are required for billing and insurance approval, but they also help track public health trends and guide research.
Why the Change Matters
Until now, all MS care used the single code G35, no matter what type of MS a person had. After October 1, insurance claims and authorizations that still list only “G35” can be delayed or denied. Accurate, up-to-date codes ensure:
- Timely coverage of infusion therapies and medications.
- Fewer billing errors, which helps keep treatment schedules on track.
- Better data for research, leading to improved understanding of MS and new therapies.
The New Codes
Your neurologist will need to document your MS subtype and disease activity:
| New Code | Description |
|---|---|
| G35A | Relapsing-remitting MS |
| G35B0 | Primary progressive MS, unspecified |
| G35B1 | Active primary progressive MS |
| G35B2 | Non-active primary progressive MS |
| G35C0 | Secondary progressive MS, unspecified |
| G35C1 | Active secondary progressive MS |
| G35C2 | Non-active secondary progressive MS |
| G35D | MS, unspecified |
A separate code (G37.9) now covers Clinically Isolated Syndrome (CIS), often the first sign of MS.
What You Can Do Now
- Check in with your prescriber. Ask if your records clearly state your MS subtype and whether new office notes or infusion orders are needed.
- Confirm upcoming appointments. If you have infusions or tests scheduled for early October, make sure the office has updated your authorization.
- Know your treatment type. Some infusion drugs—like Ocrevus®, Tysabri®, or Lemtrada®—are approved for specific MS forms. Having the right code helps avoid interruptions.
The Infusion Access Foundation is here to help patients stay on therapy without delays. Visit infusionaccessfoundation.org for resources and updates as the deadline approaches.
Companion Email Template for Patients to Send to Their Prescriber
Subject: Request to Update My Multiple Sclerosis ICD-10 Code Before October 1, 2025
Dear [Doctor/Provider Name],
I recently learned that the ICD-10 code G35 for multiple sclerosis will be retired on October 1, 2025 and replaced with new phenotype-specific codes (G35A, G35B0–B2, G35C0–C2, G35D).
Because ICD-10 codes are required for insurance authorizations and billing, I want to be sure my records are updated so my treatment continues without delays.
Could you please:
- Confirm that my chart clearly states my MS subtype and disease activity (e.g., relapsing-remitting, primary progressive active/non-active, or secondary progressive active/non-active).
- Update any office notes and infusion orders with the appropriate new ICD-10 code.
- Submit or resubmit prior authorizations using the new code for appointments on or after October 1, 2025.
Thank you for helping me stay on therapy without interruption. Please let me know if you need any information from me.
Sincerely,
[Your Name]
[Date of Birth]
[Preferred Contact Information]
[Your Name]
[Date of Birth]
[Preferred Contact Information]
