Big ICD-10 Code Changes Are Coming for Multiple Sclerosis: What Infusion Centers Need to Know

There are big changes coming from CMS with a major update to ICD-10 code G35 for multiple sclerosis. For years, all MS patients were captured under the single code G35, but beginning October 1, 2025, that will no longer be the case. Many prescribers, providers, and payers have been unknowingly preparing for this transition, since most medical policies require that a patient’s MS be documented as either primary progressive or relapsing-remitting to meet medical necessity. Because the foundation for subtype-based documentation is already in place, we are optimistic that these ICD-10 changes will not cause a significant negative impact for infusion providers. Still, preparation is essential.

So what do you need to know?

The ICD-10 Changes

As of October 1, 2025, ICD-10 code G35 (multiple sclerosis) will be retired as a stand-alone code and replaced with a parent category and new phenotype-specific subcodes. These new codes are intended to improve accuracy in documentation, disease tracking, and payer alignment.

Here are the updated MS codes:

How to Prepare

What We Know So Far

One of the biggest questions infusion providers are asking is: “Will I need to get a new authorization for every MS patient?” Based on payer feedback so far, there appears to be no consensus among payers. For example, one payer has already stated that a new prior authorization will be required with the updated ICD-10 code. While another payer reported that current authorizations are honored through their end date.

Because payer policies may vary, we strongly encourage infusion centers to contact their contracted payers now for clarification. Specifically, ask if new authorizations will be required to replace current authorizations using G35 code and if new authorizations are required, if those requests can be submitted with the updated codes for appointments scheduled in early October.

Prioritize Early October Appointments

Start reviewing your October infusion schedule now. Patients receiving treatment in the first weeks of October will be most at risk for delays if documentation and authorizations are not updated.

1. Contact prescribers to request updated clinical notes and orders that specify MS subtype and disease activity.
2. Obtain new authorizationsusing the updated ICD-10 codes.
3. Confirm system updates with your billing software, EHR vendors, and clearinghouses to ensure the new codes are available and transmitting correctly.
4. Educate staff so that coders, nurses, and front-office teams understand that G35 alone cannot be used for dates of service on or after October 1.

Critical Components to Remember

For claims submitted with dates of service on or after October 1, 2025:

• The ICD-10 code on the claim must be supported by documentation of medical necessity in the medical record.
• The ICD-10 code on the claim must match the ICD-10 code submitted on the prior authorization.
• Claims must include a valid ICD-10 code for that date of service to be paid.
  • The new ICD-10 codes are not valid for dates of service before 10/1/2025. For example, if a patient is infused on September 30 but the claim is submitted on October 1, the old G35 code must still be used since the service date was before October 1.

Bottom line: The shift from a single G35 code to phenotype-specific MS codes represents a major change, with the potential to delay patient access to treatment and reimbursement, but infusion centers can navigate the transition smoothly by preparing now. Begin updating documentation, securing new authorizations, and ensuring staff and systems are ready. Proactive steps today will reduce the risk of denials, protect revenue, and keep patients on therapy without interruption.

NICA’s Support

As this transition unfolds, NICA will continue to monitor payer responses, authorization requirements, and any reported challenges. If you encounter issues related to the ICD-10 changes, please reach out to NICA’s Payer Relations team ([email protected]) so we can escalate concerns and provide additional guidance.

Additional Resources

• ICD-10 MS Coding Update: Documentation Request Template (single patient request)
• ICD-10 MS Coding Update: Documentation Request Template (multiple patients/batch request)
• CMS FY 2026 ICD-10-CM Official Guidelines for Coding and Reporting (PDF)
• CMS ICD-10-CM FY 2026 Code Set Updates
• Subscribe to CMS updates  and never miss important policy changes.