G35.A

🧬 ICD-10 CM G35.A — Multiple Sclerosis, Unspecified

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 (unspecified MS phenotype). No additional characters are required.

Non-Billable Parent Codes — Never Submit These

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

  As of the January 2026 update, G35 has been expanded. Always submit a 4-character code (such as G35.A) to indicate the specific clinical course or its unspecified nature.

Clinical Context: "Unspecified" vs. Specific Phenotype

ICD-10 CM G35.A indicates a diagnosis of Multiple Sclerosis (MS) where the exact clinical course (e.g., Relapsing-Remitting, Primary Progressive) is not documented. If the neurologist’s note specifies the disease pattern, a more specific code (like the newly established codes for RRMS, PPMS, or SPMS) is strongly preferred over G35.A to accurately reflect disease trajectory and treatment appropriateness.

🔍 Code Description

ICD-10 CM G35.A classifies a chronic, immune-mediated inflammatory disease of the central nervous system where the specific phenotypic course is not documented in the medical record.

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.

Clinical presentation varies widely depending on the location of the lesions (plaques) 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.

🌳 Code Tree / Hierarchy

G35 Multiple sclerosis ❌ Non-billable (Expanded Jan 2026)
│

├── G35.A MULTIPLE SCLEROSIS, UNSPECIFIED ◀ THIS CODE ✅
├── G35.B Relapsing-remitting multiple sclerosis (RRMS) ✅
├── G35.C Primary progressive multiple sclerosis (PPMS) ✅
├── G35.D Secondary progressive multiple sclerosis (SPMS) ✅
└── G35.E Clinically isolated syndrome (CIS) ✅

✅ Includes

The following clinical scenarios and terms map to G35.A when the clinical course is not further specified:

• Multiple sclerosis NOS
• Disseminated sclerosis NOS
• Generalized multiple sclerosis
• Demyelinating disease of CNS, specified as MS

❌ 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 MS rely heavily on advanced neuroimaging, cerebrospinal fluid analysis, and infusion 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 Infusion Therapy

Clinical Vignette: A 42-year-old female with a known history of multiple sclerosis presents to the outpatient infusion center for her scheduled disease-modifying therapy (DMT). The specific subtype of her MS is not listed in the encounter note. She receives an intravenous infusion of a biologic agent over 2.5 hours without any adverse reactions.

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 — Multiple sclerosis, unspecified (Coded because the specific phenotype like RRMS is not documented in this visit note)

Scenario 2 — Inpatient Admission for Acute Exacerbation

Clinical Vignette: A 35-year-old male with MS is admitted from the emergency department with acute onset of severe left leg weakness and extreme fatigue over the last 3 days, consistent with an acute MS exacerbation. The admitting neurologist notes the patient’s MS subtype is unspecified in old records. The patient is admitted to the neurology floor and started on high-dose IV methylprednisolone (1000 mg/day) for 5 days.

CPT / HCPCS:

• 99222 — Initial hospital inpatient care, moderate complexity

ICD-10-CM:

• G35.A — Multiple sclerosis, unspecified (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 — CDI Query: Specifying the MS Phenotype

Clinical Vignette: A patient’s problem list merely states “Multiple Sclerosis.” However, the neurology consultation note dictates: “Patient is here for follow-up of her MS. She has had two distinct clinical relapses in the past year, with near-complete recovery between flares. MRI shows new enhancing lesions. Plan to escalate DMT.”

Action / Outcome:

If the coder uses the problem list, they will default to G35.A (Unspecified). However, the neurologist’s documentation clearly describes a “relapsing-remitting” pattern. The coder should either code from the consult note or query the provider to officially update the diagnosis to Relapsing-Remitting MS.

Corrected ICD-10-CM Coding (Instead of G35.A):

• G35.B — Relapsing-remitting multiple sclerosis (RRMS)

⚠️ Coding Pitfalls and Tips

	Pitfall or Tip
❌	Do not use the old parent code G35: As of 2026, the 3-character code is invalid. You must apply the 4th character (A, B, C, D, or E) to specify the disease state or note that it is unspecified.
❌	Do not code G35.A if the subtype is documented elsewhere: If the physician clearly notes “Primary Progressive MS” or “RRMS” in the H&P or consult, use the specific codes (G35.C or G35.B) rather than defaulting to the unspecified code G35.A.
✅	Code additional manifestations: MS affects multiple body systems. Always code additional documented symptoms such as neurogenic bladder (N31.9), muscle spasticity (M62.838), or ataxia (R27.0) if they are actively being managed.
✅	Query for specificity: “Unspecified” codes should be a last resort. Because treatment protocols differ drastically between progressive and relapsing forms of MS, CDI queries are highly recommended when the subtype is missing for established patients.

📚 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).