2027 ICD-10-CM Diagnosis Code G37.1Central demyelination of corpus callosum

ICD-10-CM Codes›G00–G99›G35-G37›G37

ICD-10-CM G37.1
CMSSource: CMS FY 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

G37.1 is a billable ICD-10-CM diagnosis code for central demyelination of corpus callosum. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 58 through 60. As a secondary diagnosis, it counts as a complication or comorbidity (CC) and moves an inpatient stay to a higher severity level within its MS-DRG family. It does not count, however, when the principal diagnosis is one of 166 closely related codes. Coders also document this condition as Marchiafava-Bignami disease. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Other nervous system disorders (neither hereditary nor degenerative).

For Medicare Advantage risk adjustment, G37.1 maps to CMS-HCC Category 198 (Multiple Sclerosis) under the V28 model, adding a risk factor of about 0.647 for a community, non-dual, aged beneficiary in payment year 2027.

Code Identity

ICD-10-CM Code
G37.1
Billable Status
Yes — Valid for Submission
Code Describes
Central demyelination of corpus callosum
Short Description
Central demyelination of corpus callosum
Same as the full description in the CMS dataset.
Parent Code
G37
Other demyelinating diseases of central nervous system

Code Classification

ChapterG00–G99Diseases of the nervous system
SectionG35-G37Demyelinating diseases of the central nervous system
CategoryG37Other demyelinating diseases of central nervous system
This CodeG37.1Central demyelination of corpus callosum

Medicare Risk Adjustment (HCC)Billing

G37.1 maps to a payment category in the CMS-HCC model used to risk-adjust Medicare Advantage payments. Weights are the published community factors for payment year 2027.

CMS-HCC V28 Category (Payment Model)
HCC 198— Multiple Sclerosis
Payment HCC · PY 2027 one of 20 ICD-10-CM codes in this category
Risk Adjustment Factor (RAF) Weight
+0.647
community, non-dual, aged · ranges 0.226–1.143 across segments
Hierarchy
Top of its hierarchy
HCC 198 is not superseded by any other condition category
Prior Model (CMS-HCC V24)
HCC 77
V24 retired V28 pays 100% of MA risk scores since PY 2026
Other CMS Models
PACE (CMS-HCC V22): HCC 77 · ESRD (V21): HCC 77 · ESRD (V24): HCC 77
ESRD V21 weights: 0.069 dialysis, 0.000–0.546 functioning graft · ESRD V24 weights: 0.111 dialysis, 0.042–1.113 functioning graft
Part D (RxHCC)
Not mapped
G37.1 does not risk-adjust in the RxHCC prescription drug model

Source: CMS Payment Year 2027 risk adjustment mappings and model software. Weights are relative factors, not dollar amounts; a beneficiary's total RAF also includes demographics and interactions. Browse all CMS-HCC categories.

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Marchiafava-Bignami disease

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to G37.1: its own notes plus those printed at Chapter 6. A note printed at a category, block or chapter applies to every code under it.

Excludes2

Not included here: the excluded condition is not part of this code, but a patient may have both, so both codes may be reported.

From Chapter 6 (G00-G99) Diseases of the nervous system applies to 700 codes
  • certain conditions originating in the perinatal period (P04-P96)
  • certain infectious and parasitic diseases (A00-B99)
  • complications of pregnancy, childbirth and the puerperium (O00-O9A)
  • congenital malformations, deformations, and chromosomal abnormalities (Q00-Q99)
  • endocrine, nutritional and metabolic diseases (E00-E88)
  • injury, poisoning and certain other consequences of external causes (S00-T88)
  • neoplasms (C00-D49)
  • symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified (R00-R94)

Source: CMS ICD-10-CM Tabular List. How to read instructional notes.

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR NVS020
Other nervous system disorders (neither hereditary nor degenerative)
Default principal diagnosis: inpatient Yes · outpatient Yes

Clinical InformationClinical

  • Marchiafava-Bignami Disease

    a rare neurological disorder characterized initially by selective demyelination and necrosis of the corpus callosum. it is associated with chronic ethanol consumption or malnutrition, and depending on the acuity of presentation, signs and symptoms may include an altered mental state, motor disturbances, seizures, delirium and coma.

Patient EducationClinical

Degenerative Nerve Diseases

Degenerative nerve diseases affect many of your body's activities, such as balance, movement, talking, breathing, and heart function. Many of these diseases are genetic. Sometimes the cause is a medical condition such as alcoholism, a tumor, or a stroke. Other causes may include toxins, chemicals, and viruses.

Read the full article at MedlinePlus

Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.

Convert G37.1 to ICD-9-CMHistory

The closest ICD-9-CM equivalents under the General Equivalence Mappings.

ICD-9-CM
341.8 Cns demyelination NEC
Approximate The match is approximate rather than exact.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2026No changes
FY 2027CurrentCurrent code set, no changesEffective October 1, 2026 through September 30, 2027.

Questions About G37.1Overview

What is the ICD-10 code for central demyelination of corpus callosum?

The ICD-10-CM code for central demyelination of corpus callosum is G37.1 (sometimes written as G371). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

Is G37.1 (Other demyelinating diseases of central nervous system) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report central demyelination of corpus callosum on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

What MS-DRG does G37.1 group to?

When central demyelination of corpus callosum is the principal diagnosis on an inpatient stay, it groups to MS-DRG 60, 58, 59, with relative weights from 0.9248 to 1.8430 depending on complications. Higher weights mean higher Medicare reimbursement.

Is G37.1 a CC or MCC?

CMS lists G37.1 as a CC (complication or comorbidity) for FY 2027. Reported as a secondary diagnosis, it moves the inpatient stay to a higher-weighted DRG within its severity family. It does not count when the principal diagnosis is one of the 166 closely related codes in its exclusion list.

What is the ICD-9 equivalent of G37.1?

Under the General Equivalence Mappings, central demyelination of corpus callosum converts to ICD-9-CM 341.8 (cns demyelination NEC). The mapping is approximate, so confirm the match fits the documentation.

What HCC is G37.1?

G37.1 (central demyelination of corpus callosum) maps to CMS-HCC Category 198 (Multiple Sclerosis), commonly written as HCC 198, in the CMS-HCC V28 model used for Medicare Advantage risk adjustment in payment year 2027. It mapped to HCC 77 under the retired V24 model. It also maps in the PACE (CMS-HCC V22), ESRD (V21), and ESRD (V24) models. It does not map to any RxHCC in the Part D prescription drug model.

Does G37.1 risk-adjust for Medicare Advantage payment?

Yes. When documented and reported on a Medicare Advantage encounter, G37.1 adds a risk adjustment factor of about 0.647 to the beneficiary's RAF score for a community, non-dual, aged enrollee (published V28 weights range from 0.226 to 1.143 depending on the payment segment). HCC 198 sits at the top of its hierarchy, so no other condition category supersedes it. See the full factor table on the HCC 198 category page.