2027 ICD-10-CM Diagnosis Code G37.4Subacute necrotizing myelitis of central nervous system
ICD-10-CM Codes›G00–G99›G35-G37›G37
- Billable — Valid for Submission
- MCC — Major Complication or Comorbidity
- Risk Adjusts — HCC 182
- Chronic Condition
G37.4 is a billable ICD-10-CM diagnosis code for subacute necrotizing myelitis of central nervous system. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 23 through 24, 97 through 99, 974 through 976. As a secondary diagnosis, it counts as a major complication or comorbidity (MCC) and places an inpatient stay in the highest severity level of its MS-DRG family. It does not count, however, when the principal diagnosis is one of 191 closely related codes. Coders also document this condition as acute necrotizing myelitis. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Other nervous system disorders (neither hereditary nor degenerative).
For Medicare Advantage risk adjustment, G37.4 maps to CMS-HCC Category 182 (Spinal Cord Disorders/Injuries) under the V28 model, adding a risk factor of about 0.478 for a community, non-dual, aged beneficiary in payment year 2027.
Code Identity
Code Classification
Medicare Risk Adjustment (HCC)Billing
G37.4 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.
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.
- Acute necrotizing myelitis
- Demyelination of spinal cord
- Subacute necrotizing myelitis
Instructional NotesGuidance
Instructions from the official ICD-10-CM Tabular List that apply to G37.4: 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.
- 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.
Referenced in Other NotesGuidance
Instructional notes printed at other codes that name G37.4, its category, or a range that includes it.
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.
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 G37.4 to ICD-9-CMHistory
Code HistoryHistory
Questions About G37.4Overview
What is the ICD-10 code for subacute necrotizing myelitis of central nervous system?
The ICD-10-CM code for subacute necrotizing myelitis of central nervous system is G37.4 (sometimes written as G374). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
Is G37.4 (Other demyelinating diseases of central nervous system) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report subacute necrotizing myelitis of central nervous system on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
What MS-DRG does G37.4 group to?
When subacute necrotizing myelitis of central nervous system is the principal diagnosis on an inpatient stay, it groups to MS-DRG 24, 98, 974, 976, 99, 975, 23, 97, with relative weights from 0.7879 to 5.7422 depending on complications. Higher weights mean higher Medicare reimbursement.
Is G37.4 a CC or MCC?
CMS lists G37.4 as an MCC (major complication or comorbidity) for FY 2027. Reported as a secondary diagnosis, it places the inpatient stay in the highest-weighted DRG of its severity family. It does not count when the principal diagnosis is one of the 191 closely related codes in its exclusion list.
What is the ICD-9 equivalent of G37.4?
Under the General Equivalence Mappings, subacute necrotizing myelitis of central nervous system converts to ICD-9-CM 323.9 (encephalitis NOS) and 341.8 (cns demyelination NEC). The mapping is approximate, so confirm the match fits the documentation.
What HCC is G37.4?
G37.4 (subacute necrotizing myelitis of central nervous system) maps to CMS-HCC Category 182 (Spinal Cord Disorders/Injuries), commonly written as HCC 182, in the CMS-HCC V28 model used for Medicare Advantage risk adjustment in payment year 2027. It mapped to HCC 72 under the retired V24 model. It also maps in the PACE (CMS-HCC V22), ESRD (V21), and ESRD (V24) models. In the Part D prescription drug model it maps to RxHCC 155.
Does G37.4 risk-adjust for Medicare Advantage payment?
Yes. When documented and reported on a Medicare Advantage encounter, G37.4 adds a risk adjustment factor of about 0.478 to the beneficiary's RAF score for a community, non-dual, aged enrollee (published V28 weights range from 0.270 to 0.478 depending on the payment segment). A more severe related category (HCC 180, HCC 181, HCC 191, and HCC 192) supersedes it when both are reported. See the full factor table on the HCC 182 category page.
