Wait— wasn’t MS one disease?
How the chaotic rollout of new ICD-10 codes for MS is reshaping care for patients and frustrating clinicians.
The irony wasn’t lost on me.
Late September, I was in Barcelona for ECTRIMS, the world’s largest conference on MS and related disorders. Sunshine. 9,500 attendees. The latest breakthroughs in MS science. Every conversation and presentation seemed to echo the same message: MS is one disease, a biological continuum with a spectrum of clinical expressions.
And yet, as I sat in sessions about unifying biology, another reality was unfolding back home. My inbox filled with messages from staff: dozens of requests to “update” my patients’ diagnoses using the new ICD-10-CM codes for MS subtypes.
Until now, we had a single administrative code—G35. Simple, unified, reflective of what we know biologically. Then, quietly and without warning, new codes appeared. Suddenly, MS had been subdivided into eight administrative categories, fragmenting on paper what scientists had finally agreed was one disease.
MS as one disease
Research tells the true story: beneath the diagnostic labels, the same biology is at work. Inflammation, demyelination, axonal injury, and neurodegeneration occur across the full spectrum of MS. Brain scans reveal overlapping patterns of new lesions and atrophy. Under the microscope, the pathology is indistinguishable. In short, the biology is unified; the differences lie in degree and timing, not in kind.
Even the so-called transition from relapsing to secondary progressive MS, which new diagnostic codes mark as a distinct boundary, unfolds gradually. Many patients straddle that line for years.
This shared biology is echoed in treatment response. Therapies developed for “relapsing MS” also benefit people with progressive disease when inflammatory activity persists. The same drugs work across subtypes because they target the same underlying process.
Defining subtypes serves an important purpose, particularly in clinical trials, where they allow researchers to assemble more homogeneous groups and evaluate treatments against consistent endpoints. But they are clinical constructs, not biological divides. For people living with MS, this distinction matters deeply. It reminds us that your disease is not defined by a code or a checkbox, but by your individual course. Seeing MS as one disease allows us to move beyond rigid categories and embrace its true continuum, recognizing that while administrative systems may require labels, the lived experience of MS is far more fluid.
Why ICD-10 codes matter?
You might ask, why does this matter? Aren’t ICD-10 codes just bureaucratic shorthand?
Well, in reality, they carry tremendous weight in how care is delivered.
Every diagnosis entered into an electronic health record is translated into one of these codes. Those codes then ripple outward. To insurance companies deciding whether to cover a medication, to hospital billing systems determining reimbursement, to registries tracking outcomes, and even to researchers analyzing patterns of disease.
For a person living with MS, that ripple can feel like a wave. The “wrong” code can mean the difference between timely access to treatment or weeks of frustrating delays. Inconsistent coding can close doors to rehabilitation, clinical trials, or specialty programs that rely on those same diagnostic labels. And for clinicians, these codes shape quality metrics, workloads, and even how resources are distributed within their health systems.
That’s why the rollout of new ICD-10 codes isn’t just a bureaucratic footnote. It’s a shift with real consequences for patients, clinicians, and the future of MS care.
How is this going to play out in the real world?
Let’s imagine what this looks like in real life.
Maria is 48 and has been living with MS for more than a decade. Early on, she experienced relapses, but a high-efficacy therapy stopped all visible disease activity. In the past few years, however, she’s noticed a gradual decline in mobility, a right foot drop that’s become more pronounced.
At her next visit, Maria’s neurologist expresses concern about her immune markers and recurrent infections. Together, they decide it’s time to switch to a different medication, something that will give her immune system a break. Before wrapping up, her neurologist mentions the new ICD-10 codes. Because Maria has shown progression after a few initial relapses, it makes sense to use the secondary progressive MS code. And since she hasn’t had a relapse in years, they agree that “non-active secondary progressive MS” (G35.C2) best describes her current status.
The prescription is sent, and the insurance claim goes out with the new code.
Two weeks later, Maria receives a letter: her medication has been denied. The explanation is blunt: the treatment is not approved for non-active SPMS. Yet, under the previous umbrella MS code, it had been on formulary and covered without issue.
Maria’s biology hasn’t changed. Her disease hasn’t changed. Only the administrative label has.
Both she and her neurologist know that while she hasn’t had a relapse in years, the risk remains if treatment stops. But continuing her current therapy is too dangerous. Maria is devastated when she learns that no disease-modifying therapy is covered under her plan for non-active SPMS.
Her neurologist, already exhausted by the wave of changes these new codes have unleashed, steels himself for another peer-to-peer review. The next morning at 8 a.m., the insurance company’s pharmacist calls. The neurologist explains Maria’s case, passionately outlining why she still needs therapy.
“Does Maria have non-active SPMS?” the pharmacist asks.
“Yes,” he answers, “that’s the best descriptor for her right now, but her history and what we know about MS tell us she’s likely to relapse without treatment.”
“I’m sorry,” the pharmacist replies. “If the diagnosis is non-active SPMS, I can’t approve this medication. You can file an appeal.”
By lunchtime, Maria’s neurologist is drained. He spends his break drafting an appeal letter and faxes it immediately. Two weeks later, Maria receives another denial. She is left without treatment options.
Maria’s story may be fictional for now, but I suspect we will see many such cases within a matter of months, if not weeks. As the case-study illustrate, clinicians and patients make decisions for treatment based on future risk, whereas diagnostic codes are descriptors of past clinical course often already modified by the use of medications. The fact that payers can decide (and deny) coverage based on codes that are not aligned with our approach to clinical decision-making will have far-reaching consequences for patients and the clinicians who care for them.
At the patient level, we can expect delays in treatment, confusion, and distress when coverage is denied for reasons outside their control. Clinicians will have to explain why a chart now says “non-active SPMS” or “active SPMS”, labels that may feel like an unexpected reclassification or, worse, like a door closing on treatment.
At the clinic level, staff are already overwhelmed by the administrative burden of resubmitting orders for medications, rehabilitation, and equipment under updated ICD-10 codes. With the inevitable rise in denials, those willing to fight will spend even more time on appeals, time taken away from patient care. I suspect that it will be difficult to convey the nuances of MS pathobiology and clinical decision-making when the new coding system is so black and white, and many of these appeals may remain denied.
Where do we go from here?
The honest answer is: I don’t know.
Most of us felt blindsided by the rollout of these new diagnostic codes. How clinicians respond will be worth watching and I suspect it’ll look different across settings.
Most clinicians will do what they have to do for billing and insurance, meaning they’ll use the new codes even if they don’t fully agree with the distinctions. But there’s already frustration that these codes don’t reflect how we actually understand MS biology.
Neurologists are likely to anticipate denials when prescribing disease-modifying therapies, especially for people labeled with “non-active SPMS,” a category that currently has no approved treatment options, even though treatment may be needed to stay non-active. To navigate this, some may document even subtle signs of activity - a faint MRI change, a questionable relapse - to justify coding as “active SPMS” so their patients don’t lose access to therapy. Others may use the G35.D “Unspecified MS” code instead, though how payers will interpret that remains to be seen.
At this point, people living with MS need to be aware of the change. Ask your doctor which code they plan to use and how it might affect coverage for your medications or services.
Clinicians, for our part, need support and clarity, as well as flexibility from payers. Professional and patient organizations like the American Academy of Neurology, National MS Society, and MS Association of America should start collecting real-world examples of potential harm caused by coding-related denials. These stories matter. They often drive the revisions and policy updates that data alone can’t.
And I’d also challenge manufacturers to stay engaged, to keep supporting access to medications, even as denials increase.
I’m deeply interested in your thoughts on this.
If you’re living with MS, have these new codes affected your care?
If you’re a clinician, how are you approaching the new requirements?
Thank you for drawing attention to this issue, for your fictional but realistic example of how this could play out for patients and for your practical call to action. We look forward to working alongside you to understand the challenges and to influence change where we can.
Excellent post. These codes are geared to benefit the payers, not the patients, while HCPs are working to benefit their patients. These goals are at odds and the payers seem to hold all the cards. This needs to change.