multiple sclerosis

DEFINITION of multiple sclerosis

Multiple sclerosis (MS) is a chronic, immune-mediated demyelinating disease of the central nervous system (CNS) in which autoreactive T-lymphocytes and B-cells breach the blood-brain barrier and attack the myelin sheath — the lipid-rich insulating layer encasing nerve axons — triggering focal inflammatory lesions called plaques that progress to gliotic scars (sclerosis) throughout the brain, spinal cord, and optic nerves. Destruction of myelin and eventual axonal loss disrupts the speed and fidelity of electrical impulse conduction along affected neural pathways, producing the hallmark clinical syndrome: relapsing or progressive neurological dysfunction that can affect motor function, sensation, vision, cognition, bladder control, and coordination. The disease course is classified into four primary phenotypes — relapsing-remitting (RRMS), primary progressive (PPMS), secondary progressive (SPMS), and clinically isolated syndrome (CIS) — each with distinct biology, prognosis, and therapeutic approach. MS is the most common nontraumatic disabling neurological disease in young adults, disproportionately affecting women and those of Northern European descent, with onset typically between ages 20-40. As an inpatient profee coder, MS is a high-impact diagnosis across neurology, medicine, and rehabilitation admissions — and FY2026 brought one of the biggest MS coding overhauls in a decade: G35 is now a parent code and is no longer billable. You must drill down to G35.A, G35.B0-G35.B2, G35.C0-G35.C2, or G35.D based on documented disease course AND activity status. Every MS admission should trigger a documentation query if the neurologist hasn’t specified subtype and current activity — the difference between active and non-active disease can drive HCC risk adjustment and DRG weight in meaningful ways.

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ETYMOLOGY of multiple sclerosis

latin greek

Component	Origin	Meaning
multi-	Latin multus	”Many / multiple” — indicating the plural, disseminated nature of the lesions throughout the CNS
-ple	Latin -plex (from plectere)	“Fold / layer” — combined with multi- to form multiple, meaning “consisting of many parts”
scler-	Ancient Greek σκληρός (sklērós)	“Hard” — referring to the hardened, gliotic scar tissue (sclerotic plaques) that form at sites of demyelination
-osis	Greek noun-forming suffix -ωσις (-ōsis)	“Condition of / abnormal process” — denotes a pathological state or process, particularly one of degeneration or accumulation

The term multiple sclerosis was coined by French neurologist Jean-Martin Charcot in 1868, who used it to describe the multiple hardened (sclerotic) plaques he observed on autopsy of patients who had suffered recurring episodes of neurological dysfunction. The descriptor multiple captured the hallmark dissemination of lesions throughout the white matter of the CNS — a feature now formalized as dissemination in space (DIS) in the 2018 McDonald diagnostic criteria. The combining form scler- (Greek: hard) gave rise to sclerosis, arteriosclerosis, atherosclerosis, and amyotrophic lateral sclerosis (ALS) — all sharing the concept of pathological hardening of tissue. The term disseminated sclerosis was also used historically and persists as an alias under the ICD-10-CM G35.D descriptor.

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🔀 ALIASES / ALTERNATE TERMS

• MS (universal clinical abbreviation)
• RRMS (relapsing-remitting MS — most common form; ~85% of initial diagnoses; characterized by discrete relapses followed by partial or complete recovery)
• PPMS (primary progressive MS — steady neurological decline from onset without early relapses; ~10-15% of cases; coded with activity status in G35.B0-B2)
• SPMS (secondary progressive MS — transition from RRMS to a progressive course, with or without ongoing relapses; coded G35.C0-C2)
• Clinically Isolated Syndrome (CIS) (first demyelinating episode not yet meeting McDonald criteria for MS; coded G37.9 in ICD-10-CM 2026)
• Radiologically Isolated Syndrome (RIS) (incidental MS-like MRI lesions without clinical symptoms)
• Disseminated sclerosis (historical alias; still listed as inclusion term under G35.D)
• Generalized multiple sclerosis (older synonym; listed under G35.D)
• Lhermitte’s sign (electric shock sensation on neck flexion; classic MS symptom from cervical cord lesion)
• McDonald criteria (2018 diagnostic framework requiring dissemination in space (DIS) and time (DIT) via MRI and/or CSF)
• Uhthoff’s phenomenon (transient worsening of symptoms with increased body temperature — heat sensitivity pathognomonic of MS)
• Pseudoexacerbation (MS symptom worsening due to fever/infection, NOT a true relapse — important distinction for coding and clinical management)

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🔗 RELATED TERMS

• Myelin — the lipid-rich insulating sheath surrounding nerve axons; the primary target of immune attack in MS
• Oligodendrocyte — the CNS cell responsible for producing and maintaining myelin; destroyed in MS lesions
• demyelination — pathologic stripping of the myelin sheath from axons; the fundamental pathologic process in MS
• Plaque — focal area of demyelination and gliosis in the CNS; the histopathologic unit of MS; visible as hyperintense lesions on MRI T2/FLAIR
• Gliosis — reactive scarring by astrocytes at sites of demyelination; the “sclerosis” in multiple sclerosis
• Relapse / Exacerbation / Attack — episode of new or worsening neurological symptoms lasting >24 hours, attributable to a new or newly active CNS lesion
• Remission — period of stability or partial/complete recovery of function between relapses in RRMS
• EDSS (Expanded Disability Status Scale) — standard scoring tool for MS disability level; 0-10 scale; critical for treatment decisions and DMT selection
• McDonald criteria — 2018 diagnostic framework; requires DIS + DIT via clinical findings, MRI, and/or CSF oligoclonal bands
• Oligoclonal bands (OCB) — IgG bands found on CSF electrophoresis; present in ~85-90% of MS patients; supports diagnosis
• Optic neuritis — inflammation of the optic nerve; common MS presentation and CIS manifestation; coded H46.11/H46.12
• Transverse myelitis — inflammatory spinal cord lesion; common MS relapse presentation; may be coded separately
• JC virus / PML (Progressive Multifocal Leukoencephalopathy) — life-threatening brain infection caused by JC virus; risk associated with natalizumab therapy
• Disease-modifying therapy (DMT) — class of agents that reduce relapse rate and slow disability progression in MS (interferons, glatiramer, natalizumab, ocrelizumab, siponimod, etc.)
• Ocrelizumab (Ocrevus) — first FDA-approved treatment for PPMS; anti-CD20 B-cell depleting agent; given via IV infusion every 6 months
• Natalizumab (Tysabri) — anti-VLA-4 monoclonal antibody; IV infusion every 4 weeks; associated with PML risk via JC virus reactivation
• Interferon beta (Avonex, Betaseron, Rebif) — first-generation injectable DMTs; reduce relapse frequency in RRMS
• Glatiramer acetate (Copaxone) — synthetic polypeptide injectable; immunomodulatory; first-line RRMS therapy
• Methylprednisolone — high-dose IV corticosteroid; standard acute relapse treatment; shortens relapse duration (not long-term disability)
• Plasmapheresis / PLEX — therapeutic plasma exchange; used for severe steroid-refractory relapses

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CODING CORNER

🏥 ICD-10-CM CODES

Multiple Sclerosis — Category G35

(Under Chapter 6: Diseases of the Nervous System; Block G35-G37: Demyelinating diseases of the CNS) (⚠️ FY2026 UPDATE: G35 is now a PARENT CODE — it is NO LONGER BILLABLE as of October 1, 2025. You MUST use a subcategory.)

Relapsing-Remitting MS

Code	Description
G35.A	Relapsing-remitting multiple sclerosis (RRMS — most common form; ~85% of new diagnoses; discrete relapses with recovery periods) — ⚠️ HCC

Primary Progressive MS — Category G35.B

(Steady neurological decline from symptom onset; no early relapses; document activity status based on MRI and clinical findings)

Code	Description
G35.B0	Primary progressive multiple sclerosis, unspecified activity (use only if activity status not documented)
G35.B1	Active primary progressive multiple sclerosis (with evidence of inflammatory disease activity — new/enlarging MRI lesions or clinical worsening) — ⚠️ HCC
G35.B2	Non-active primary progressive multiple sclerosis (without inflammatory disease activity — stable on imaging) — ⚠️ HCC

Secondary Progressive MS — Category G35.C

(Transition from RRMS to progressive course; may or may not have ongoing relapses; document activity status)

Code	Description
G35.C0	Secondary progressive multiple sclerosis, unspecified activity (use only if activity status not documented)
G35.C1	Active secondary progressive multiple sclerosis (with ongoing relapses or new MRI lesions despite progressive course) — ⚠️ HCC
G35.C2	Non-active secondary progressive multiple sclerosis (progressive without current inflammatory activity) — ⚠️ HCC

Unspecified MS

Code	Description
G35.D	Multiple sclerosis, unspecified (includes: disseminated MS, generalized MS, MS NOS — use as last resort only) — ⚠️ HCC

Clinically Isolated Syndrome & Demyelinating Disease

Code	Description
G37.9	Demyelinating disease of central nervous system, unspecified (now used for Clinically Isolated Syndrome / CIS in FY2026)
G36.0	Neuromyelitis optica (NMO / Devic disease) (Excludes1 from G35 — distinct entity, not MS)
G36.1	Acute and subacute hemorrhagic leukoencephalitis (Hurst disease)
G36.8	Other specified acute disseminated demyelination

Common MS Manifestations & Associated Codes

(Code additionally when documented as separate manifestations)

Code	Description
H46.11	Retrobulbar neuritis, right eye (optic neuritis — common MS manifestation)
H46.12	Retrobulbar neuritis, left eye
H46.8	Other optic neuritis
G35.A	(see above — optic neuritis may be the presenting CIS that evolves to RRMS)
R20.2	Paraesthesia of skin (numbness/tingling — MS sensory symptom)
G81.10	spastic hemiplegia affecting unspecified side (MS motor complication)
G82.20	paraplegia, unspecified (severe MS spinal cord involvement)
N31.9	Neuromuscular dysfunction of bladder, unspecified (neurogenic bladder — common MS complication)
G35.A	(document MS as cause when coding neurogenic bladder, spasticity, or cognitive dysfunction in MS patients)
R41.3	Other amnesia / cognitive impairment (MS-related cognitive dysfunction)
G89.29	Other chronic pain (MS-related neuropathic pain when not further specified)

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🔧 COMMON CPT CODES (MS-Related Procedures, Diagnostics & Infusions)

Neuroimaging — MRI Brain & Spine

(Primary diagnostic and monitoring tool for MS lesion burden and disease activity)

CPT Code	Description
70551	MRI brain without contrast (initial lesion detection; T2/FLAIR periventricular and juxtacortical lesions)
70552	MRI brain with contrast (gadolinium-enhancing lesions indicate active inflammation/breakdown of BBB)
70553	MRI brain without and with contrast (preferred protocol for MS workup — detects both active and chronic lesions)
72141	MRI cervical spine without contrast
72142	MRI cervical spine with contrast (cord lesions; Lhermitte’s sign workup)
72146	MRI thoracic spine without contrast
72147	MRI thoracic spine with contrast
72148	MRI lumbar spine without contrast
72149	MRI lumbar spine with contrast
0866T	Quantitative MRI brain analysis with comparison to prior study; lesion detection, characterization, quantification, and brain volume — add-on to primary MRI (iCobrain MS / Icometrix — used for longitudinal MS monitoring)

Neurophysiology / Evoked Potentials

(Tests nerve conduction along demyelinated pathways — supports DIS documentation)

CPT Code	Description
95930	Visual evoked potential (VEP) testing (detects optic nerve demyelination even without clinical optic neuritis; supports MS diagnosis)
95925	Short-latency somatosensory evoked potential study (SSEP) (upper limbs — detects cervical cord/sensory pathway demyelination)
95926	Short-latency SSEP (lower limbs)
95927	Short-latency SSEP (trunk or head)
95938	Short-latency SSEP; upper and lower limbs combined

Cerebrospinal Fluid / Lumbar Puncture

CPT Code	Description
62270	Spinal puncture, lumbar, diagnostic (LP for CSF analysis — oligoclonal bands, IgG index, cell count)
83519	Immunoassay for analyte other than antibody or antigen, quantitative (CSF IgG, kappa free light chains)
86235	Nuclear antigen antibody panel (ANA — rule out SLE/CTD overlap mimicking MS)
86255	Fluorescent antibody; screen, each antibody (AQP4-IgG / NMO antibody — rule out neuromyelitis optica)
86596	Anti-myelin oligodendrocyte glycoprotein antibody (MOG-IgG) (MOGAD workup — seronegative MS mimicker)

DMT Infusion Administration

(High-value profee line items on MS infusion visits — verify provider order and supervision level)

CPT Code	Description
96365	IV infusion, therapeutic/prophylactic/diagnostic; initial, up to 1 hour (natalizumab/Tysabri, ocrelizumab/Ocrevus, ofatumumab — initial hour)
96366	IV infusion, each additional hour (add-on to 96365 — ocrelizumab infusion typically ~3.5 hours)
96367	IV infusion, additional sequential drug, up to 1 hour (if second drug infused sequentially same encounter)
96368	IV infusion, concurrent, each additional drug (concurrent second drug infusion)
96413	Chemotherapy administration, IV infusion, up to 1 hour (cyclophosphamide — used off-label for aggressive MS/HSCT prep)
96415	Chemotherapy administration, IV infusion, each additional hour (add-on to 96413)

Acute Relapse Treatment — IV Steroids

CPT Code	Description
96365	IV infusion, initial, up to 1 hour (IV methylprednisolone — standard acute relapse treatment; 1g/day × 3-5 days)
96366	IV infusion, each additional hour (add-on for prolonged methylprednisolone infusions)

Therapeutic Apheresis

(For steroid-refractory severe MS relapses)

CPT Code	Description
36514	Therapeutic apheresis; for plasma pheresis (PLEX/plasmapheresis — steroid-refractory MS relapse; typically 5-7 exchanges)

Rehabilitation & Functional Assessment

CPT Code	Description
97110	Therapeutic exercises (PT for MS-related weakness, spasticity, balance — 15-minute units)
97112	Neuromuscular reeducation (PT/OT for balance and coordination deficits)
97530	Therapeutic activities (ADL retraining — OT for MS functional limitations)
97542	Wheelchair management/propulsion training (MS mobility aid training)
97750	Physical performance test and measurement with written report (EDSS-related functional testing)
96125	Standardized cognitive performance testing per hour (neuropsychological testing for MS cognitive impairment)

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⚠️ Coding Note: G35 is no longer a valid billable code as of October 1, 2025 — it is now a parent header only. Every MS claim must use G35.A, G35.B0-G35.B2, G35.C0-G35.C2, or G35.D. If the neurologist’s documentation simply states “multiple sclerosis” without subtype and activity status, that’s a query opportunity before billing — subtype and activity documentation directly impacts HCC risk adjustment scores (CMS-HCC V28 category 198) and supports medical necessity for high-cost DMTs. Never use G35.D (unspecified) if the chart contains any documentation of disease course — push for specificity every time. G37.9 is now the designated code for Clinically Isolated Syndrome (CIS) — the first demyelinating event that doesn’t yet meet McDonald criteria for MS — don’t assign a G35.x code until MS is formally diagnosed. When coding ocrelizumab (Ocrevus) infusions, 96365 + 96366 for the additional hours are both separately billable and frequently missed on profee claims — ocrelizumab infusions routinely run 3+ hours. 0866T (quantitative MRI brain analysis/iCobrain MS) is an add-on code to the primary MRI that is increasingly used for MS monitoring — it must be billed as an add-on and cannot stand alone. For inpatient profee, always check whether the admission was triggered by an acute relapse (IV steroids driving the admission) vs. an elective DMT infusion — the principal diagnosis selection differs significantly and impacts DRG assignment.

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DERIVATIONS of multiple sclerosis

TABLE definition AS Definition
FROM #medterm
WHERE length(filter(roots, (word) => econtains([[multiple sclerosis]].roots, word))) > 0 AND file.name != [[multiple sclerosis]].file.name
SORT file.name ASC

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Query functionality

TABLE definition AS Definition
FROM #medterm 
WHERE file.name != this.file.name
AND any(contains(this.definition, definition))

Med roots Appendix A Prefixes Appendix B Combining Forms Appendix C Suffixes Appendix D Suffix forms