Crystal's MCW Coder Hub🧬 ICD-10 CM G35.C2 — Primary Progressive Multiple Sclerosis with Active Disease Progression
Billable Code Confirmed
ICD-10 CM G35.C2 is a valid, billable 5-character ICD-10-CM code for FY2026. All required characters are present:
G35(category) +.C(primary progressive phenotype) +2(with active disease progression). No additional characters are required.
Non-Billable Parent Codes — Never Submit These
- ❌
G35— 3-character header — missing phenotype and progression status- ❌
G35.C— 4-character header — missing progression/exacerbation statusAlways submit G35.C2 (all 5 characters) when PPMS is documented with clinical or radiographic evidence of active progression.
Clinical Context: "Active Progression" vs. "Acute Exacerbation"
ICD-10 CM G35.C2 captures a critical clinical distinction in modern MS management. While an acute exacerbation (G35.C1) implies a sudden, rapid inflammatory attack (relapse) over days to weeks, active disease progression (
C2) indicates objective, measurable worsening of the disease—either clinically (e.g., worsening Expanded Disability Status Scale [EDSS] score) or radiographically (e.g., new T2 or gadolinium-enhancing lesions on MRI)—over months, without the presence of a sudden acute flare. This is often referred to clinically as Progression Independent of Relapse Activity (PIRA).
Code Classification
ICD-10-CM Diagnosis Code — Fields for wRVU, assistant payable, and global period are not applicable. For associated inpatient profee and facility procedure coding, see the CPT Procedural Crosswalk and ICD-10-PCS Crosswalk sections below.
🔍 Code Description
ICD-10 CM G35.C2 classifies Primary progressive multiple sclerosis with active disease progression. It denotes a specific trajectory of this immune-mediated demyelinating disease where the patient is experiencing a documented, continuous accumulation of neurologic disability and/or active neuroinflammation on imaging, distinct from their stable baseline.
In PPMS, the autoimmune attack on the myelin sheath and the underlying axons leads to a steady decline in function. The modifier “with active disease progression” indicates that the physician has identified a notable worsening in the patient’s condition since previous evaluations. This code is crucial because it often justifies the medical necessity to initiate, switch, or escalate high-cost Disease-Modifying Therapies (DMTs) such as anti-CD20 monoclonal antibodies.
🌳 Code Tree / Hierarchy
G35 Multiple Sclerosis ❌ Non-billable
│
├── G35.A Multiple sclerosis, unspecified ✅ Billable
├── G35.B Relapsing-remitting multiple sclerosis (RRMS) ❌ Non-billable
│ │
│ ├── G35.B0 RRMS without acute exacerbation ✅ Billable
│ └── G35.B1 RRMS with acute exacerbation ✅ Billable
│
├── G35.C Primary progressive multiple sclerosis (PPMS) ❌ Non-billable
│ │
│ ├── G35.C0 PPMS without acute exacerbation ✅ Billable
│ ├── G35.C1 PPMS with acute exacerbation ✅ Billable
│ └── G35.C2 PPMS WITH ACTIVE DISEASE PROGRESSION ◀ THIS CODE ✅ Billable
│
├── G35.D Secondary progressive multiple sclerosis (SPMS) ❌ Non-billable
│ │
│ ├── G35.D0 SPMS without acute exacerbation ✅ Billable
│ ├── G35.D1 SPMS with acute exacerbation ✅ Billable
│ └── G35.D2 SPMS with active disease progression ✅ Billable
│
└── G35.E Clinically isolated syndrome (CIS) ✅ Billable
Specificity Drives Treatment Approval
PPMS represents only 10-15% of all MS cases. Capturing the “active progression” status (G35.C2) is often a prerequisite mandated by payers for the approval of advanced biologic therapies. Documenting and coding this status accurately prevents prior authorization denials and ensures continuity of care.
✅ Includes
The following clinical terms and scenarios map to G35.C2 when documented for a PPMS patient:
- Active primary progressive MS
- PPMS with active MRI lesions (new or enlarging T2/FLAIR, or Gd-enhancing)
- PPMS with clinical worsening or progressing EDSS score
- PPMS with progression independent of relapse activity (PIRA)
❌ Excludes
Excludes 1 — Cannot Be Coded Simultaneously with G35.C2
| Code | Description | Note |
|---|---|---|
| G36.0 | Neuromyelitis optica [Devic] | Mutually exclusive — NMO involves antibodies targeting aquaporin-4 (AQP4); pathophysiology is distinct from MS. Code G36.0 instead if NMO is confirmed. |
| G36.9 | Acute disseminated demyelination | ADEM is typically a monophasic post-infectious process, unlike the chronic, progressive nature of PPMS. |
| G37.81 | MOGAD | Myelin oligodendrocyte glycoprotein antibody-associated disease is a distinct demyelinating syndrome with different clinical progression. |
Excludes 1 Violation Risk
You cannot assign MS codes concurrently with other specified central demyelinating diseases like NMO or MOGAD. If a patient’s diagnosis is revised from MS to NMO based on autoantibody testing, use the NMO code exclusively.
Excludes 2 — May Be Coded in Addition if Separately Present
| Code | Description | Note |
|---|---|---|
| G37.- | Other demyelinating diseases of central nervous system | May be coded additionally if a completely distinct condition is present. |
📋 Clinical Overview
Phenotype Distinction — Understanding “Active Progression”
The 2026 MS category expansion requires coders to distinguish not only the phenotype but the current disease activity. This distinction must be explicitly documented by the neurologist.
| Feature | Active Progression (G35.C2) | Acute Exacerbation (G35.C1) | Without Exacerbation / Stable (G35.C0) |
|---|---|---|---|
| Clinical Presentation | Insidious, measurable worsening over months (e.g., walking distance decreased from 100m to 50m over 6 months). | Sudden, rapid onset of new neurological symptoms over 24-48 hours. | Baseline disability remains steady without measurable decline between visits. |
| Radiographic Presentation | Often shows slowly expanding lesions (SELs) or subtle new T2 lesions on annual MRI. | Characterized by large, active gadolinium-enhancing lesions on immediate MRI. | No new MRI activity compared to prior scan. |
| Primary Treatment Response | Optimization of long-term DMTs (e.g., adjusting infusion intervals). | High-dose IV corticosteroids (e.g., methylprednisolone) or plasmapheresis. | Continue current maintenance therapy. |
CDI Query Trigger — "PPMS doing worse"
If the physician documents a PPMS patient is “doing worse” or “declining,” a CDI query is warranted to clarify if this constitutes an acute exacerbation (G35.C1) or active disease progression (G35.C2). This differentiation drastically impacts MS-DRG grouping, medical necessity for IV steroids, and outpatient infusion coverage.
Manifestations & Symptom Burden
Patients with active progression typically exhibit a worsening of baseline symptoms, commonly including:
- Progressive spastic paraparesis: Increased stiffness and profound weakness in the lower extremities.
- Worsening ataxia: Increased fall risk and loss of balance.
- Neurogenic bowel/bladder decline: Progression to complete retention or incontinence.
- Severe cognitive/fatigue decline: Increased impairment affecting daily living.
Coding Manifestations
Always code the documented manifestations to fully capture the patient’s complexity. These codes support the medical decision making (MDM) regarding progression. Examples include:
💰 HCC Risk Adjustment (CMS-HCC v28)
| Field | Detail |
|---|---|
| CMS-HCC Model Version | v28 (2024-2025 Implementation) |
| HCC Assignment | ✅ Mapped |
| HCC Category | HCC 77 — Multiple Sclerosis |
| RAF Coefficient | ~0.45 - 0.65 (varies by demographic/status) |
G35.C2 maps directly to an HCC and contributes significantly to the RAF score.
Capture Annually
Even though PPMS is a lifelong condition, it must be evaluated, documented, and coded at least once every calendar year to be calculated in the patient’s risk profile. The
C2character specifically signals a high-risk, high-cost year ahead due to active disease.
🏥 MS-DRG Assignment
MDC 01 — Diseases and Disorders of the Nervous System
| DRG | Title | Est. Relative Weight* |
|---|---|---|
| DRG 058 | Multiple Sclerosis & Cerebellar Ataxia with MCC | ~1.30 - 1.50 |
| DRG 059 | Multiple Sclerosis & Cerebellar Ataxia with CC | ~0.90 - 1.10 |
| DRG 060 | Multiple Sclerosis & Cerebellar Ataxia without CC/MCC | ~0.65 - 0.80 |
Approximate. Verify against IPPS FY2026 Final Rule tables.
Sequencing and Complications
A patient with G35.C2 is highly susceptible to inpatient admissions for complications of their progression (e.g., severe UTI, falls/fractures, aspiration). When admitted for a complication, sequence the acute complication as the principal diagnosis. G35.C2 acts as a powerful Comorbidity (CC) that accurately increases the DRG weight to reflect the severe neurologic baseline.
🔗 Related ICD-10-CM Codes
Progression / Exacerbation Variants
| Code | Description |
|---|---|
| G35.C2 | PPMS with active disease progression ← This Code |
| G35.C1 | PPMS with acute exacerbation |
| G35.C0 | PPMS without acute exacerbation / stable |
Phenotype Variants
| Code | Description |
|---|---|
| G35.B1 | Relapsing-remitting multiple sclerosis with acute exacerbation |
| G35.D2 | Secondary progressive multiple sclerosis with active disease progression |
| G35.A | Multiple sclerosis, unspecified |
🛠️ Commonly Associated CPT Codes (Neurology / PM&R)
Outpatient and Profee Setting Context
The CPT codes below are frequently associated with confirming active progression and managing the escalated therapy for PPMS in profee and outpatient settings.
| CPT Code | Description | Profee Coding Notes (Modifier 26) |
|---|---|---|
| 70553 | MRI brain without contrast, followed by contrast | Standard for detecting active Gd-enhancing lesions signifying progression. Append -26 if interpreting in a facility. |
| 72156 | MRI cervical spine without and with contrast | Crucial for PPMS which heavily targets the spinal cord. Append -26 for profee. |
| 99215 | E/M established patient, high complexity | Worsening PPMS requiring therapy changes routinely meets high MDM criteria. |
| 96365 | Intravenous infusion, for therapy; initial, up to 1 hour | Frequently used for administering DMTs (e.g., Ocrelizumab). |
| 96366 | Intravenous infusion, each additional hour | Required for prolonged biologic infusions. |
NCCI Bundling Considerations
- Infusion services (96365) billed on the same day as an E/M visit (99215) require the E/M to be significant and separately identifiable (e.g., the neurologist evaluating the new MRI and diagnosing active progression prior to the infusion). Modifier -25 must be appended to the E/M code.
🔬 ICD-10-PCS Crosswalk (Inpatient Procedures)
When G35.C2 is an inpatient diagnosis, these PCS codes are relevant for interventions targeting disease progression.
| PCS Section | Body System | Root Operation | Clinical Application |
|---|---|---|---|
| 3 (Administration) | E (Physiological Systems) | 0 (Introduction) | Infusion of Disease-Modifying Therapy. Example: 3E033GC (Intro of Other Therapeutic Sub into Peripheral Vein). |
| 0 (Medical & Surgical) | 0 (Central Nervous System) | H (Insertion) | Implantation of intrathecal baclofen pump for severe, progressing spasticity. Example: 00H00MZ (Insertion of Infusion Device into Brain/Meninges). |
💊 Coding Scenarios and Examples
Scenario 1 — Outpatient Neurology Evaluation: Confirming Progression
Clinical Vignette: A 48-year-old female with PPMS presents for her annual neurology follow-up. The neurologist notes that her EDSS score has increased from 4.0 to 5.5 over the last 12 months, and she now requires a cane for ambulation. Her recent brain and C-spine MRIs show two new T2 hyperintense lesions in the cervical cord. Impression: Primary progressive MS with active clinical and radiographic progression. The provider plans to switch her therapy regimen.
CPT / HCPCS (Profee):
- 99215 — Office or other outpatient visit, established patient, high complexity
ICD-10-CM:
- G35.C2 — Primary progressive multiple sclerosis with active disease progression
- Z99.81 — Dependence on supplemental oxygen (if applicable, though in this case, focus on mobility)
- R26.2 — Difficulty in walking, not elsewhere classified
Scenario 2 — Inpatient Admission for Dysphagia Complication
Clinical Vignette: A 62-year-old male with advanced PPMS with active disease progression is admitted to the hospital with severe aspiration pneumonia. His wife notes his swallowing has progressively worsened over the last few months due to his MS decline. He requires IV antibiotics and speech therapy evaluation for a PEG tube.
Principal Diagnosis:
- J69.0 — Pneumonitis due to inhalation of food and vomit (Reason for admission)
Secondary Diagnoses:
- G35.C2 — Primary progressive multiple sclerosis with active disease progression (Captures the severe baseline driving the dysphagia; acts as a CC)
- R13.10 — Dysphagia, unspecified
MS-DRG Assignment: - The aspiration pneumonia principal diagnosis groups this to MDC 04 (Respiratory System). The inclusion of G35.C2 as a CC elevates the DRG (e.g., DRG 194 - Simple Pneumonia and Pleurisy with CC).
Scenario 3 — CDI Query: Clarifying “Doing Worse”
Clinical Vignette: A patient is seen in the outpatient infusion center. The clinic note states: “Patient with PPMS is here for scheduled infusion. Note that she is doing worse recently with increased leg weakness over the last 4 months.”
Action / Outcome: If a coder relies strictly on the current default, they might code G35.C0 (PPMS without acute exacerbation). However, “doing worse over 4 months” implies active disease progression. A CDI query should be sent to clarify if the patient meets the criteria for active progression.
Query Response: The physician updates the documentation to confirm “Active clinical progression of PPMS.”
Corrected ICD-10-CM Coding:
- G35.C2 — Primary progressive multiple sclerosis with active disease progression
- M62.81 — Muscle weakness (generalized)
⚠️ Coding Pitfalls and Tips
| Pitfall or Tip | |
|---|---|
| ❌ | Do not confuse G35.C2 (Active Progression) with G35.C1(Acute Exacerbation). Exacerbations are sudden, short-term inflammatory attacks. Progression is a measurable decline in baseline over months/years or new MRI activity without a sudden flare. |
| ❌ | Do not code G35.A (Unspecified) if documentation provides clues. If the note says “Progressing PPMS,” you must use the specific C2 character. |
| ✅ | Always append Modifier -25 correctly. If billing a high-level E/M (99215) to discuss active progression on the same day as a biologic infusion (96365), ensure Modifier -25 is appended to the E/M. |
| ✅ | Sequence acute complications first for inpatients. In an inpatient setting, if the patient is admitted for a fall or pneumonia secondary to progression, code the acute condition first. G35.C2 is sequenced secondarily but remains critical for DRG CC/MCC capture. |
| ✅ | Capture all manifestations. Documenting specific manifestations (dysphagia, ataxia, muscle weakness) paints a clear picture of the MDM complexity and the nature of the progression. |
📚 Sources
- CMS/NCHS. ICD-10-CM Official Guidelines for Coding and Reporting, FY2026. 2. National Multiple Sclerosis Society. Types of MS: Primary Progressive MS and Disease Activity.
- Lublin, F. D., et al. (2014). Defining the clinical course of multiple sclerosis: the 2013 revisions. Neurology, 83(3), 278-286. (Source for PIRA and Active/Progressing clinical definitions).
- CMS. 2025-2026 Medicare Advantage Risk Adjustment — CMS-HCC Model v28 ICD-10-CM Mappings. 5. CMS. IPPS Final Rule FY2026 — MS-DRG Definitions Manual v43. MDC 01 logic tables.
- AMA. CPT Professional Edition 2026. Neurology and Medicine subsections.