G35.A

🧬 ICD-10 CM G35.A — Relapsing-Remitting Multiple Sclerosis (RRMS)

Billable Code Confirmed

ICD-10 CM G35.A is a valid, billable 4-character ICD-10-CM code effective for FY2026. All required characters are present: G35 (category) + .A (relapsing-remitting phenotype). No additional characters are required.

Non-Billable Parent Codes — Never Submit These

• ❌ G35 — 3-character header — missing phenotype specification

  As of the FY2026 update, G35 has been expanded. The legacy 3-character G35 is non-billable. Always submit a 4-character code (such as G35.A) to indicate the specific clinical course or its unspecified nature.

Clinical Context: RRMS as a Specific Phenotype

ICD-10 CM G35.A identifies Relapsing-Remitting Multiple Sclerosis (RRMS) — the disease course defined by discrete clinical relapses (attacks) followed by periods of full or partial recovery, with no clinical progression between relapses. This is the most common MS phenotype at onset (~85% of cases). Code G35.A only when the relapsing-remitting course is documented; if the subtype is not stated, use G35.D (Multiple sclerosis, unspecified) instead.

🔍 Code Description

ICD-10 CM G35.A classifies relapsing-remitting multiple sclerosis, a chronic, immune-mediated inflammatory disease of the central nervous system characterized by clearly defined acute relapses with full or partial recovery and a stable, non-progressive clinical course between attacks.

In patients with MS, the immune system mounts an autoimmune attack against myelin—the protective sheath covering nerve fibers—and the underlying axons themselves. This leads to demyelination and the formation of scar tissue (sclerosis) in the brain and spinal cord, disrupting the transmission of electrical signals.

In RRMS specifically, inflammatory activity produces episodic relapses (also called attacks, exacerbations, or flares) that evolve over days, plateau, and then remit. Between relapses the patient is neurologically stable, distinguishing RRMS from the progressive forms:

• Primary progressive MS (PPMS, G35.B) — steady accumulation of disability from onset, without distinct early relapses.
• Secondary progressive MS (SPMS, G35.C) — begins as RRMS, then transitions to gradual progression with or without superimposed relapses.

Clinical presentation of an RRMS relapse varies with lesion (plaque) location and may include:

• Visual disturbances (e.g., optic neuritis)
• Severe fatigue
• Muscle weakness, spasticity, or ataxia
• Sensory changes (paresthesia, numbness)
• Bowel or bladder dysfunction

Note

The diagnosis of MS relies on the McDonald criteria, requiring evidence of central nervous system lesions that are disseminated in both “space” (different parts of the CNS) and “time” (occurring at different points in time), alongside the exclusion of other demyelinating conditions. The relapsing-remitting pattern of attacks with recovery is the clinical hallmark supporting G35.A.

🌳 Code Tree / Hierarchy

G35 Multiple sclerosis ❌ Non-billable (Expanded FY2026)
│
├── G35.A Relapsing-remitting multiple sclerosis (RRMS) ◀ THIS CODE ✅
│
├── G35.B Primary progressive multiple sclerosis (PPMS) ❌ Non-billable header
│   ├── G35.B0 Primary progressive MS, unspecified ✅
│   ├── G35.B1 Primary progressive MS, active ✅
│   └── G35.B2 Primary progressive MS, not active ✅
│
├── G35.C Secondary progressive multiple sclerosis (SPMS) ❌ Non-billable header
│   ├── G35.C0 Secondary progressive MS, unspecified ✅
│   ├── G35.C1 Secondary progressive MS, active ✅
│   └── G35.C2 Secondary progressive MS, not active ✅
│
└── G35.D Multiple sclerosis, unspecified ✅

✅ Includes

The following clinical scenarios and terms map to G35.A when a relapsing-remitting course is documented:

• Relapsing-remitting multiple sclerosis (RRMS)
• Multiple sclerosis with relapses and remissions
• MS with documented relapse and recovery, no progression between attacks
• Active relapsing-remitting MS (relapse/new enhancing lesion documented)

❌ Excludes

Excludes1 — Cannot be coded together

The Excludes1 note dictates that the following conditions cannot be coded alongside G35.A. They represent distinct pathophysiologic mechanisms or alternative demyelinating diseases:

• Neuromyelitis optica [Devic] (G36.0)
• Acute disseminated demyelination (G36.9)
• Schilder’s disease (G37.0)
• Myelin oligodendrocyte glycoprotein antibody-associated disease (MOGAD) (G37.81)

Excludes2 — Can be coded together if both are present

• Other demyelinating diseases of central nervous system (G37.-)

🛠️ CPT Procedural Crosswalk — wRVU & Assistant Payable Status

Diagnosis and management of RRMS rely heavily on advanced neuroimaging, cerebrospinal fluid analysis, and infusion-based disease-modifying therapies. Below are the most common procedural CPT codes paired with G35.A.

CPT Code	Description	wRVU (Facility)	Asst. Surgeon Payable?	Co-Surgeon Payable?
70551	MRI brain without contrast material	1.18	No (Indicator 0)	No (Indicator 0)
70553	MRI brain without contrast, followed by with contrast	1.75	No (Indicator 0)	No (Indicator 0)
62270	Spinal puncture, lumbar, diagnostic	1.36	No (Indicator 0)	No (Indicator 0)
96365	Intravenous infusion, for therapy, prophylaxis, or diagnosis; initial, up to 1 hour	0.60	No (Indicator 0)	No (Indicator 0)
96366	Intravenous infusion, each additional hour	0.19	No (Indicator 0)	No (Indicator 0)

Note: wRVU values are estimates based on the standard CMS Physician Fee Schedule. Check current year exact values.

💊 Coding Scenarios

Scenario 1 — Outpatient DMT Infusion for RRMS

Clinical Vignette: A 42-year-old female with documented relapsing-remitting multiple sclerosis presents to the outpatient infusion center for scheduled disease-modifying therapy. She receives an intravenous infusion of ocrelizumab over 2.5 hours without adverse reaction. Her neurologist’s note confirms an RRMS course with two relapses in the prior 18 months and full inter-relapse recovery.

CPT / HCPCS:

• 96365 — IV infusion, initial, up to 1 hour
• 96366 x2 — IV infusion, each additional hour (capturing the remaining 1.5 hours)

ICD-10-CM:

• G35.A — Relapsing-remitting multiple sclerosis (Phenotype documented in the encounter note)

Scenario 2 — Inpatient Admission for Acute Relapse

Clinical Vignette: A 35-year-old male with known RRMS is admitted from the emergency department with acute onset of severe left leg weakness and extreme fatigue over 3 days, consistent with an acute MS relapse. He is started on high-dose IV methylprednisolone (1000 mg/day) for 5 days. The neurologist documents a relapsing-remitting course with prior recovery between attacks.

CPT / HCPCS:

• 99222 — Initial hospital inpatient care, moderate complexity

ICD-10-CM:

• G35.A — Relapsing-remitting multiple sclerosis (Principal diagnosis representing the reason for admission)
• G81.94 — Hemiplegia, unspecified affecting left nondominant side (Capturing the neurologic deficit)
• R53.83 — Other fatigue (Capturing the severe symptom burden)

Scenario 3 — Established RRMS on Maintenance Therapy

Clinical Vignette: A patient with a firm diagnosis of relapsing-remitting MS is seen for routine follow-up. The neurology note reads: “RRMS, stable. Two distinct clinical relapses over the past year with near-complete recovery between flares; surveillance MRI shows one new enhancing lesion. Continue natalizumab; counseled on PML risk and JCV status.”

Action / Outcome:

The documentation clearly establishes a relapsing-remitting course, so G35.A is the correct, fully specified code — no provider query is needed. Capture the active DMT regimen and any documented manifestations. Only when the subtype is not documented should the coder default to G35.D (MS, unspecified).

ICD-10-CM:

• G35.A — Relapsing-remitting multiple sclerosis

⚠️ Coding Pitfalls and Tips

	Pitfall or Tip
❌	Do not use the old parent code G35: As of FY2026, the 3-character code is non-billable. You must apply the 4th character to specify the disease course (A = RRMS) or use G35.D when it is unspecified.
✅	G35.A is RRMS specifically: Assign G35.A only when the record documents a relapsing-remitting course — discrete relapses with recovery and no progression between attacks. Do not use it as a generic “MS” code.
❌	Do not confuse RRMS with the progressive forms: Primary progressive MS uses the G35.B series (B0/B1/B2) and secondary progressive MS uses the G35.C series (C0/C1/C2). These require active/not-active specificity that RRMS does not.
✅	Use G35.D when the subtype is undocumented: If the provider only states “multiple sclerosis” without a phenotype, assign G35.D (Multiple sclerosis, unspecified) rather than defaulting to G35.A. Query for specificity when clinically appropriate.
✅	Code additional manifestations: RRMS affects multiple body systems. Always code documented symptoms actively being managed, such as neurogenic bladder (N31.9), muscle spasticity (M62.838), or ataxia (R27.0).

🩺 Risk Adjustment (CMS-HCC)

HCC Mapping

Under the CMS-HCC v28 model, multiple sclerosis (including G35.A RRMS) maps to HCC 198 — Multiple Sclerosis.

⚠️ Do not use HCC 77 — that is the legacy v24 number for this condition. For current payment years, the correct v28 category is HCC 198. Always confirm against the active CMS HCC crosswalk for the applicable model version and payment year.

📚 Sources

1. CMS/NCHS. ICD-10-CM Official Guidelines for Coding and Reporting, FY2026. Tabular List — G35 Multiple Sclerosis.
2. American Medical Association (AMA). CPT 2026 Professional Edition.
3. National Multiple Sclerosis Society. Diagnostic Criteria for MS (McDonald Criteria) and MS disease courses (RRMS, PPMS, SPMS).
4. CMS. CMS-HCC Risk Adjustment Model (v28) — Disease Hierarchy and Category Crosswalk.