ICD-10 Code G35: Multiple Sclerosis 2025 Essential Medical Billing updates

Multiple sclerosis ICD 10 code G35 classifies one of the most common demyelinating diseases affecting the nervous system. This condition primarily affects young adults, typically beginning between ages 20 and 40, and shows higher prevalence in women than men. A recent study involving 1,091 children and adolescents with MS found that 72.2% were female, with diagnosis occurring at an average age of 15.7 years.

The ICD-10 code for multiple sclerosis (G35) falls under diseases of the nervous system classification. Understanding this specific code is essential for accurate medical billing and proper documentation. Multiple sclerosis is characterized by the destruction of myelin in the central nervous system, leading to weakness, numbness, coordination problems, and vision disturbances. Although there is no cure for multiple sclerosis, available treatments may slow disease progression and help manage symptoms.

As you prepare for the 2025 medical billing updates, it's crucial to understand the nuances of code G35 and its documentation requirements. Proper coding not only ensures accurate reimbursement but also supports appropriate patient care through precise diagnosis classification. This guide explores the essential aspects of multiple sclerosis coding, from clinical features to specific 2025 updates that will impact your medical billing practices.

What does ICD-10 Code G35 represent in 2025?

In the 2025 ICD-10-CM codebook, G35 specifically designates multiple sclerosis, a complex neurological condition affecting the central nervous system. This code remains billable for reimbursement purposes through September 30, 2025 and is classified as a chronic condition requiring ongoing medical attention.

What conditions are included under G35?

Code G35 encompasses several variants of multiple sclerosis, creating a comprehensive classification for this demyelinating disorder. The inclusion terms specifically cover:

• Disseminated multiple sclerosis
• Generalized multiple sclerosis
• Multiple sclerosis NOS (Not Otherwise Specified)
• Multiple sclerosis of brain stem
• Multiple sclerosis of cord

G35 serves as the sole dedicated code for multiple sclerosis, unlike other neurological conditions that may have multiple subcodes. This simplifies documentation while still acknowledging the various presentations of the disease. Furthermore, G35 represents an autoimmune disorder primarily affecting young adults, characterized by the destruction of myelin in the central nervous system.

How is G35 classified in ICD-10 Chapter VI?

Within the ICD-10 hierarchical structure, G35 falls under Chapter VI: Diseases of the Nervous System (G00-G99). More specifically, it belongs to the block G35-G37, which covers demyelinating diseases of the central nervous system. This classification block includes three distinct categories:

• G35: Multiple sclerosis
• G36: Other acute disseminated demyelination
• G37: Other demyelinating diseases of central nervous system

This placement within the coding hierarchy reflects the pathophysiological nature of multiple sclerosis as a demyelinating condition. Additionally, for Diagnostic Related Group (DRG) classification purposes, G35 maps to MS-DRGs 058-060, depending on the presence of complications or comorbidities.

What are the official descriptors for G35?

The official descriptor for G35 is simply "Multiple sclerosis". Nevertheless, the World Health Organization and Centers for Medicare & Medicaid Services provide additional clarification through inclusion terms that expand upon this primary descriptor.

The code lacks exclusion notes, which means no conditions must be coded elsewhere when using G35. This straightforward coding approach simplifies documentation requirements while maintaining clinical specificity. The 2025 edition of ICD-10-CM maintains these descriptors with no significant changes from previous versions.

For clinical classification purposes, G35 is categorized under the Clinical Classification Software Refined (CCSR) category NVS005, designated as the default assignment for both inpatient and outpatient principal diagnoses.

What are the clinical features of multiple sclerosis relevant to coding?

Understanding the clinical features of multiple sclerosis is crucial for accurate ICD-10 code G35 assignment. Multiple sclerosis represents an autoimmune disorder primarily affecting young adults, characterized by destruction of myelin in the central nervous system.

What are the early signs of multiple sclerosis?

Inflammation of optic nerves (optic neuritis) is typically the first symptom of multiple sclerosis. This early manifestation often resolves within one to two weeks, causing many patients to forgo medical attention. Consequently, this crucial diagnostic indicator may be overlooked. Symptoms of optic neuritis include:

• Unilateral visual impairment (described as "seeing through fog")
• Pain (especially upon movement) in or behind the eye
• Impaired color perception and contrast sensitivity
• Abnormal pupillary response

For coding purposes, documenting these early manifestations supports medical necessity and helps establish the timeline of disease progression, essential for proper G35 application.

How does demyelination affect the nervous system?

During multiple sclerosis, the immune system (specifically white blood cells and T cells) attacks the insulating layer of nerve fibers (myelin sheath), resulting in demyelination of axons. This immune-mediated process causes inflammation primarily in the white matter of the central nervous system. As a result, nerve conduction—the transmission of information to and from the brain—becomes significantly compromised.

Pathologic findings include multiple sharply demarcated areas of demyelination throughout the white matter of the central nervous system. These lesions form the basis for diagnosis through the principle of "lesions disseminated in space and time," meaning MS plaques occur in multiple parts of the CNS over time.

What are the common symptoms linked to G35?

Clinical manifestations documented for G35 coding include visual loss, extra-ocular movement disorders, paresthesias, loss of sensation, weakness, dysarthria, spasticity, ataxia, and bladder dysfunction. Moreover, fatigue (persistent exhaustion) and worsening of symptoms with temperature increases (Uhthoff's phenomenon) are characteristic findings.

The disease pattern typically presents as recurrent attacks followed by partial recovery (relapsing-remitting MS), though acute fulminating and chronic progressive forms also occur. Indeed, after approximately 15-20 years, about half of people initially diagnosed with relapsing MS transition to secondary progressive MS, characterized by gradual worsening between attacks.

How has ICD-10 Code G35 changed in the 2025 update?

The 2025 coding cycle maintains the stability of ICD-10 code G35 for multiple sclerosis, with minimal structural changes. According to the official updates, the 2025 edition of ICD-10-CM G35 became effective on October 1, 2024, and remains valid through September 30, 2025. This continuity helps ensure consistent documentation practices for medical billing professionals dealing with multiple sclerosis cases.

What are the new inclusions or exclusions for G35?

No new inclusions or exclusions have been added specifically to the G35 code in the 2025 update. The code continues to maintain its existing applicable terms, including disseminated multiple sclerosis, generalized multiple sclerosis, multiple sclerosis NOS, multiple sclerosis of brain stem, and multiple sclerosis of cord. Notably, the Centers for Medicare & Medicaid Services (CMS) announced that while there were 50 new ICD-10-PCS procedure codes effective April 1, 2025, no new ICD-10-CM diagnosis codes were introduced during this update cycle.

Are there any revised descriptors or notes?

The April 2025 diagnosis code update primarily addresses revisions and typographical errors rather than substantive changes to the G35 code. The basic descriptor remains "Multiple sclerosis" without modification. The Type 2 Excludes notes continue to apply across the G00-G99 chapter, directing coders to use separate codes for conditions like infectious diseases, neoplasms, and pregnancy complications when they occur alongside multiple sclerosis.

How does G35 relate to other demyelinating codes like G36 or G37?

G35 exists within a structured relationship with codes G36 (Other acute disseminated demyelination) and G37 (Other demyelinating diseases of central nervous system):

• These three codes collectively form the complete G35-G37 block covering all demyelinating diseases of the central nervous system
• G36 includes conditions like neuromyelitis optica [Devic] (G36.0) and acute hemorrhagic leukoencephalitis (G36.1)
• G37 contains specific demyelinating conditions including diffuse sclerosis (G37.0) and myelin oligodendrocyte glycoprotein antibody disease (G37.81)

For DRG grouping purposes in 2025, G35 maps to MS-DRG codes 058-060 (Multiple sclerosis and cerebellar ataxia), with the specific assignment depending on whether major complications or comorbidities exist.

How should G35 be used in medical billing and documentation?

Proper coding practices for multiple sclerosis using ICD-10 code G35 directly impact reimbursement outcomes and claims processing. Medical billers must understand several critical aspects of G35 usage to avoid denials and ensure appropriate payment.

What are the DRG groupings for G35 in 2025?

For inpatient stays, G35 maps to three possible MS-DRG groupings under version 42.0, effective April 1, 2025:

• 058: Multiple sclerosis and cerebellar ataxia with major complication or comorbidity (MCC)
• 059: Multiple sclerosis and cerebellar ataxia with complication or comorbidity (CC)
• 060: Multiple sclerosis and cerebellar ataxia without CC/MCC

The assigned DRG directly affects reimbursement levels, with higher payments for cases involving complications. Documentation must clearly establish any complications to support appropriate DRG assignment and prevent revenue loss.

Can G35 be used as a primary diagnosis code?

G35 is absolutely acceptable as a first-listed or primary diagnosis code. Despite this, confusion exists among some payers and electronic lookup systems. Certain sources incorrectly indicate that G35 requires an F02 or F48 code listed first.

Surprisingly, some insurance companies, such as Ambetter in Indiana, have erroneously denied claims with G35 as the primary diagnosis. Upon provider follow-up, Ambetter acknowledged these denials were mistakes and agreed to reprocess the claims correctly. If you encounter similar denials, promptly contact the payer for claim resubmission.

What are common billing errors associated with G35?

Several documentation and coding pitfalls occur when billing for multiple sclerosis:

• Using the general G35 code when a more specific subtype is documented
• Insufficient documentation of symptoms or disease progression
• Missing documentation of treatment plans related to the diagnosis
• Failure to document functional status, which supports medical necessity

Such errors potentially lead to three significant consequences: inappropriate treatment decisions, increased audit risk, and potential reimbursement loss due to insufficient supporting documentation.

Since October 1, 2015, all claims must use ICD-10-CM codes like G35 rather than the previous ICD-9-CM code 340. This cutoff date remains important for historical claims processing and compliance reviews.

Conclusion

What are the key takeaways for medical billers handling MS cases?

Understanding ICD-10 code G35 remains essential for medical billing professionals dealing with multiple sclerosis patients in 2025. Throughout this guide, you have learned that G35 continues to be a billable code through September 30, 2025, with no significant structural changes from previous versions. Furthermore, this code encompasses several variants of multiple sclerosis, including disseminated, generalized, and NOS presentations.

Medical billers should be aware that although G35 is absolutely acceptable as a primary diagnosis, some payers have erroneously denied such claims. Therefore, staying vigilant about incorrect denials and promptly addressing them prevents revenue loss. The consistent classification of multiple sclerosis under the demyelinating diseases block (G35-G37) also helps clarify its relationship with other similar neurological conditions.

Last but certainly not least, maintaining thorough documentation of disease progression, treatment plans, and functional status not only supports proper coding but also reduces audit risk. As you navigate the 2025 medical billing landscape, this comprehensive understanding of G35 will undoubtedly strengthen your coding accuracy and reimbursement success for multiple sclerosis cases.

FAQs

Q1. What is the ICD-10 code for multiple sclerosis?

The ICD-10 code for multiple sclerosis is G35. This code is used to classify and identify multiple sclerosis in medical billing and documentation.

Q2. Is G35 a billable code for multiple sclerosis?

Yes, G35 is a billable code for multiple sclerosis. It can be used to specify a diagnosis on reimbursement claims, provided it meets the applicable criteria for the patient's condition.

Q3. How has the ICD-10 code G35 changed in the 2025 update?

The ICD-10 code G35 for multiple sclerosis has remained largely unchanged in the 2025 update. It continues to be valid through September 30, 2025, with no significant structural changes or new inclusions/exclusions.

Q4. Can G35 be used as a primary diagnosis code?

Yes, G35 can be used as a primary or first-listed diagnosis code. However, some insurance companies have erroneously denied claims with G35 as the primary diagnosis, so it's important to be aware of this potential issue and address it promptly if it occurs.

Q5. What are the DRG groupings for G35 in 2025?

In 2025, G35 maps to three possible MS-DRG groupings: 058 (with major complication or comorbidity), 059 (with complication or comorbidity), and 060 (without CC/MCC). The specific assignment depends on the presence of complications or comorbidities.

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