🧬 ICD-10 CM G35.C0 — Secondary Progressive Multiple Sclerosis, Unspecified
Billable Code Confirmed
ICD-10 CM G35.C0 is a valid, billable 5-character ICD-10-CM code for FY2026. All required characters are present:
G35(category) +.C(secondary progressive phenotype) +0(activity status unspecified).
Non-Billable Parent Codes — Never Submit These
- ❌
G35— 3-character header — missing phenotype and activity status- ❌
G35.C— 4-character header — missing activity statusAlways submit G35.C0 (all 5 characters) when SPMS is documented but disease activity (active vs. non-active) is not specified.
Clinical Context: "Secondary Progressive" vs. Other Phenotypes
ICD-10 CM G35.C0 specifically identifies Secondary Progressive Multiple Sclerosis (SPMS). SPMS begins as Relapsing-Remitting MS (RRMS) and later transitions into a phase of steady neurologic progression, with or without occasional superimposed relapses. This is fundamentally different from Primary Progressive MS (PPMS, the G35.B0 family), which is progressive from onset with no prior relapsing course. The trailing
0indicates the documentation does not specify whether the disease is currently active or non-active.
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.C0 classifies Secondary progressive multiple sclerosis, unspecified. It denotes an immune-mediated demyelinating disease of the central nervous system in which the clinical course began as relapsing-remitting disease and has since transitioned to steady, progressive accumulation of disability.
In SPMS, the inflammatory, relapse-driven activity that characterized the earlier RRMS phase gives way to a more neurodegenerative process — progressive axonal loss and CNS atrophy — that produces gradually worsening function (often gait, balance, and lower-extremity strength) independent of discrete attacks. Some patients continue to have occasional relapses superimposed on the progression, while others progress without them.
The qualifier “unspecified” means the medical record documents the secondary progressive phenotype but does not state whether the disease is currently active (recent relapse and/or new MRI lesion activity) or non-active. When activity status is documented, a more specific code is required: G35.C1 (active) or G35.C2 (non-active).
🌳 Code Tree / Hierarchy
G35 Multiple Sclerosis ❌ Non-billable
│
├── G35.A Relapsing-remitting multiple sclerosis (RRMS) ✅ Billable
│
├── G35.B Primary progressive multiple sclerosis (PPMS) ❌ Non-billable
│ │
│ ├── G35.B0 PPMS, unspecified ✅ Billable
│ ├── G35.B1 PPMS, active ✅ Billable
│ └── G35.B2 PPMS, not active ✅ Billable
│
├── G35.C Secondary progressive multiple sclerosis (SPMS) ❌ Non-billable
│ │
│ ├── G35.C0 SPMS, UNSPECIFIED ◀ THIS CODE ✅ Billable
│ ├── G35.C1 SPMS, active ✅ Billable
│ └── G35.C2 SPMS, not active ✅ Billable
│
└── G35.D Multiple sclerosis, unspecified ✅ Billable
Specificity is Key for Proper Care Management
Recognizing the transition from RRMS to SPMS reshapes the treatment strategy: relapse-focused disease-modifying therapies become less effective as inflammatory activity wanes, and management shifts toward progression-targeted agents and rehabilitation. Documenting whether the SPMS is active or non-active (G35.C1 vs. G35.C2) further refines therapy selection. Capturing the G35.C- family justifies the medical necessity for these specific care pathways.
✅ Includes
The following clinical terms and scenarios map to G35.C0 when SPMS is documented without a stated activity status:
- Secondary progressive MS (SPMS) NOS
- Secondary progressive multiple sclerosis, activity status not documented
- SPMS following a known relapsing-remitting course, current activity not specified
❌ Excludes
Excludes 1 — Cannot Be Coded Simultaneously with G35.C0
| 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 SPMS. |
| G37.81 | MOGAD | Myelin oligodendrocyte glycoprotein antibody-associated disease is a distinct demyelinating syndrome. |
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 — The Critical Factor
The MS category expansion requires coders to distinguish the disease trajectory. This distinction must be explicitly documented by the neurologist.
| Feature | Secondary Progressive (SPMS) | Relapsing-Remitting (RRMS) | Primary Progressive (PPMS) |
|---|---|---|---|
| Disease Course | Begins as RRMS, then transitions to steady progression (± occasional relapses). | Unpredictable attacks followed by periods of remission. | Steady decline from onset, no prior relapsing course. |
| Typical Onset | Emerges ~10-20 years after an initial RRMS diagnosis. | Usually younger (age 20-30), highly female-predominant. | Usually older (age 40+), roughly equal male-to-female ratio. |
| Common Presentation | Gradually worsening mobility/spasticity despite few or no obvious flares. | Optic neuritis, sensory changes, focal brainstem signs. | Progressive myelopathy (spinal cord involvement), gait issues. |
| Code Family | G35.C- series (This code) | G35.A | G35.B- series |
CDI Query Trigger — "Multiple Sclerosis" NOS
If the physician documents only “Multiple Sclerosis” for a patient clearly on a DMT or with a long history of the disease, a CDI query is warranted. The difference between RRMS, PPMS, and SPMS dictates risk adjustment, care pathways, and payer approvals. Defaulting to G35.D (Unspecified) should be a last resort.
Manifestations & Symptom Burden
The symptoms of G35.C0 reflect the patient’s progressive baseline trajectory. These often include:
- Progressive spastic paraparesis: Stiffness and weakness in the legs.
- Neurogenic bowel/bladder: Urgency, retention, or incontinence.
- Cognitive changes: Processing speed delays.
- Severe fatigue: Often disproportionate to the physical exertion.
Coding Manifestations
Always code the documented manifestations to fully capture the patient’s complexity, especially in the inpatient profee setting where evaluation and management of these specific symptoms drive the E/M level. Examples include:
💰 HCC Risk Adjustment (CMS-HCC v28)
| Field | Detail |
|---|---|
| CMS-HCC Model Version | v28 (2024-2025 Implementation) |
| HCC Assignment | ✅ Mapped |
| HCC Category | HCC 198 — Multiple Sclerosis |
| RAF Coefficient | ~0.45 - 0.65 (varies by demographic/status) |
G35.C0 maps directly to an HCC and contributes significantly to the RAF score.
Verify the Crosswalk and Capture Annually
Under CMS-HCC v28, Multiple Sclerosis maps to HCC 198 (this replaces the old v24 number, HCC 77). Confirm the current mapping against the active CMS HCC crosswalk for the payment year. Even though SPMS is a lifelong, incurable condition, it must be evaluated, documented, and coded at least once every calendar year to be calculated in the patient’s risk profile.
🏥 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.
MS as a Secondary Diagnosis
While an admission strictly for SPMS is rare, SPMS patients are frequently admitted for complications (e.g., severe pressure ulcers, urosepsis, aspiration pneumonia). When G35.C0 is a secondary diagnosis, it often functions as a crucial Comorbidity (CC) that accurately increases the DRG weight to reflect the intensive nursing and physical therapy requirements.
🔗 Related ICD-10-CM Codes
Activity Status Variants (Secondary Progressive)
Phenotype Variants
| Code | Description |
|---|---|
| G35.A | Relapsing-remitting multiple sclerosis (RRMS) |
| G35.B0 | Primary progressive multiple sclerosis, unspecified |
| G35.D | Multiple sclerosis, unspecified |
🛠️ Commonly Associated CPT Codes (Neurology / PM&R)
Outpatient and Profee Setting Context
The CPT codes below are associated with the diagnostic workup and management of SPMS in profee and outpatient settings.
| CPT Code | Description | Profee Coding Notes (Modifier 26) |
|---|---|---|
| 70551 | MRI brain without contrast material | Append -26 if the physician is only interpreting the imaging in a facility setting. |
| 72141 | MRI cervical spine without contrast | SPMS often carries a heavy cervical cord lesion burden. |
| 62270 | Spinal puncture, lumbar, diagnostic | Used to check for oligoclonal bands. |
| 96365 | Intravenous infusion, for therapy, prophylaxis, or diagnosis; initial, up to 1 hour | Frequently used for administering DMTs. |
| 96366 | Intravenous infusion, each additional hour |
NCCI Bundling Considerations
- When coding 62270 (lumbar puncture), fluoroscopic guidance (77003) is typically bundled depending on the payer, but may be billed separately with appropriate modifiers if distinct medical necessity is documented.
- Infusion services (96365) billed on the same day as an E/M visit require the E/M to be significant and separately identifiable (Modifier -25).
🔬 ICD-10-PCS Crosswalk (Inpatient Procedures)
When G35.C0 is an inpatient diagnosis and a procedure is performed (e.g., during an admission for severe disease progression requiring inpatient rehab transfer or complication management), these PCS codes are relevant.
| 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) | 9 (Drainage) | Diagnostic Lumbar Puncture. Example: 009U3ZX (Drainage of Spinal Canal, Percutaneous, Diagnostic). |
| 0 (Medical & Surgical) | 0 (Central Nervous System) | H (Insertion) | Implantation of intrathecal baclofen pump for severe, refractory spasticity associated with SPMS. |
💊 Coding Scenarios and Examples
Scenario 1 — Outpatient Biologic Infusion (Profee / Outpatient Facility)
Clinical Vignette: A 52-year-old female with a long-standing history of MS that began as relapsing-remitting disease and has, over the past several years, transitioned to a steadily progressive course presents to the outpatient infusion center for scheduled DMT therapy. The neurologist documents “secondary progressive MS” but does not characterize current disease activity. Infusion lasts exactly 2.5 hours without complication.
CPT / HCPCS (Profee/Outpatient):
- 96365 — IV infusion, initial, up to 1 hour
- 96366 x2 — IV infusion, each additional hour
- DMT HCPCS J-code — code units based on exact dosage
ICD-10-CM:
- G35.C0 — Secondary progressive multiple sclerosis, unspecified
- R26.89 — Other abnormalities of gait and mobility (Supports the clinical picture of slow decline)
Query Opportunity
Scenario 2 — Admitted for Sepsis, SPMS as Comorbidity (Inpatient Facility)
Clinical Vignette: A 60-year-old female with advanced secondary progressive MS (wheelchair dependent, neurogenic bladder managed with indwelling Foley) is admitted from the ER for altered mental status and hypotension. Blood and urine cultures are positive for E. coli. She is treated with IV antibiotics for severe sepsis. Her MS phenotype is documented as secondary progressive, but activity status is not specified.
Principal Diagnosis:
- A41.51 — Sepsis due to Escherichia coli (Reason for admission)
Secondary Diagnoses:
- N39.0 — Urinary tract infection, site not specified
- G35.C0 — Secondary progressive multiple sclerosis, unspecified (Crucial secondary diagnosis driving nursing care burden)
- N31.9 — Neuromuscular dysfunction of bladder, unspecified
- Z99.3 — Dependence on wheelchair
- Z46.6 — Encounter for fitting and adjustment of urinary device (Foley catheter)
MS-DRG Assignment: - The sepsis principal diagnosis groups this to MDC 18. The inclusion of G35.C0 and other complexities acts as a CC, properly adjusting the DRG weight (e.g., DRG 871 - Septicemia or Severe Sepsis w/o MV >96 Hours w/ MCC, if an MCC is present, or DRG 872 w/ CC).
Scenario 3 — CDI Query: Clarifying the Disease Course
Clinical Vignette: The H&P for a patient admitted to the inpatient rehab unit states: “Patient with a 15-year history of MS, originally relapsing-remitting, now with steadily worsening lower extremity weakness over the last 3 years and few discrete attacks. Admitted for intensive physical therapy and baclofen pump optimization.”
Action / Outcome: If a coder relies solely on the term “multiple sclerosis,” they would assign G35.D (Unspecified). However, the clinical description (RRMS that has shifted to steady progression) points to a secondary progressive phenotype. A CDI query should be sent to the attending physician to confirm the phenotype — and, ideally, the current activity status.
Query Response: The physician updates the documentation to “Secondary Progressive MS,” but does not state whether it is active or non-active.
Corrected ICD-10-CM Coding:
- G35.C0 — Secondary progressive multiple sclerosis, unspecified
- Z51.89 — Encounter for other specified aftercare (Baclofen pump optimization)
One More Query Layer
⚠️ Coding Pitfalls and Tips
| Pitfall or Tip | |
|---|---|
| ❌ | Do not default to G35.D (Unspecified) if documentation provides clues. If the note says “SPMS,” “PPMS,” or “RRMS,” you must use the specific phenotype code. |
| ❌ | Do not confuse secondary progressive (G35.C-) with primary progressive (G35.B-). SPMS begins as RRMS and then transitions to progression; PPMS is progressive from onset with no prior relapsing course. |
| ❌ | Do not invent an activity status. G35.C0 is the correct code only when active vs. non-active is not documented. If the record states active disease, use G35.C1; if explicitly stable/non-active, use G35.C2. Query when it is unclear. |
| ✅ | Sequence properly. In an inpatient setting, if the patient is admitted for an acute issue (e.g., pneumonia, UTI, fracture), code the acute condition first. G35.C0 is sequenced secondarily but remains critical for DRG capture and risk adjustment. |
| ✅ | Capture all manifestations. For profee coders, capturing the specific manifestations (spasticity, neurogenic bladder, fatigue) paints a clear picture of the Medical Decision Making (MDM) complexity, supporting higher level E/M codes. |
| ✅ | Append Modifier -26 correctly. If billing profee for diagnostic testing (MRIs, OCTs) performed in a hospital setting, ensure Modifier -26 is appended so you are only billing for the professional interpretation. |
📚 Sources
- CMS/NCHS. ICD-10-CM Official Guidelines for Coding and Reporting, FY2026.
- National Multiple Sclerosis Society. Types of MS: Secondary Progressive MS.
- CMS. 2025-2026 Medicare Advantage Risk Adjustment — CMS-HCC Model v28 ICD-10-CM Mappings.
- CMS. IPPS Final Rule FY2026 — MS-DRG Definitions Manual v43. MDC 01 logic tables.
- CMS. ICD-10-PCS Reference Manual FY2026. Section 0 (Central Nervous System), Section 3 (Administration).
- AMA. CPT Professional Edition 2026. Neurology and Medicine subsections.