2027 ICD-10-CM Diagnosis Code G93.42Megalencephalic leukoencephalopathy with subcortical cysts

ICD-10-CM Codes›G00–G99›G89-G99›G93

ICD-10-CM G93.42
CMSSource: CMS FY 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

G93.42 is a billable ICD-10-CM diagnosis code for megalencephalic leukoencephalopathy with subcortical cysts. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 70 through 72, 974 through 976. 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 9 closely related codes. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Other nervous system disorders (often hereditary or degenerative).

For Medicare Advantage risk adjustment, G93.42 maps to CMS-HCC Category 200 (Friedreich and Other Hereditary Ataxias; Huntington Disease) under the V28 model, adding a risk factor of about 0.279 for a community, non-dual, aged beneficiary in payment year 2027.

Code Identity

ICD-10-CM Code
G93.42
Billable Status
Yes — Valid for Submission
Code Describes
Megalencephalic leukoencephalopathy with subcortical cysts
Short Description
Megalencephalic leukoencephalopathy with subcortical cysts
Same as the full description in the CMS dataset.
Parent Code
G93.4
Other and unspecified encephalopathy

Code Classification

ChapterG00–G99Diseases of the nervous system
SectionG89-G99Other disorders of the nervous system
CategoryG93Other disorders of brain
This CodeG93.42Megalencephalic leukoencephalopathy with subcortical cysts

Medicare Risk Adjustment (HCC)Billing

G93.42 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 200— Friedreich and Other Hereditary Ataxias; Huntington Disease
Payment HCC · PY 2027 one of 17 ICD-10-CM codes in this category
Risk Adjustment Factor (RAF) Weight
+0.279
community, non-dual, aged · ranges 0.000–0.428 across segments
Hierarchy
Top of its hierarchy
HCC 200 is not superseded by any other condition category
Prior Model (CMS-HCC V24)
HCC 52
V24 retired V28 pays 100% of MA risk scores since PY 2026
Other CMS Models
ESRD (V21): HCC 52 · ESRD (V24): HCC 52
ESRD V21 weights: 0.045 dialysis, 0.000–0.328 functioning graft · ESRD V24 weights: 0.042 dialysis, 0.000–0.399 functioning graft
Part D (RxHCC)
Not mapped
G93.42 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.

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to G93.42: its own notes plus those printed at G93.4 and 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 G93.4 Other and unspecified encephalopathy applies to 7 codes
  • alcoholic encephalopathy (G31.2)
  • encephalopathy in diseases classified elsewhere (G94)
  • hypertensive encephalopathy (I67.4)
  • toxic (metabolic) encephalopathy (G92.8)
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.

Referenced in Other NotesGuidance

Instructional notes printed at other codes that name G93.42, its category, or a range that includes it.

Code Also 1

These codes say G93.42 may also be needed to fully describe the condition. The note gives no sequencing direction.

  • F78.A1 SYNGAP1-related intellectual disability
    encephalopathy (G93.4-) names G93.4-, which includes this code

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 NVS006
Other nervous system disorders (often hereditary or degenerative)
Default principal diagnosis: inpatient Yes · outpatient Yes

Patient EducationClinical

Leukodystrophies

Leukodystrophies are a group of rare genetic disorders that affect the central nervous system (CNS). The CNS is made up of your brain and spinal cord. Leukodystrophies damage the white matter of your CNS. The white matter includes:

The full article covers:

  • What are leukodystrophies?
  • What causes leukodystrophies?
  • What are the symptoms of leukodystrophies?
  • How are leukodystrophies diagnosed?
  • What are the treatments for leukodystrophies?

Read the full article at MedlinePlus

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

Code History & ChangesHistory

Replacement G93.42 replaces the following previously assigned code(s):

  • G93.49 - Other encephalopathy
FY 2024AddedAdded to the ICD-10-CM code setEffective October 1, 2023.
FY 2025RevisedCode revised
FY 2026No changes
FY 2027CurrentCurrent code set, no changesEffective October 1, 2026 through September 30, 2027.

Questions About G93.42Overview

What is the ICD-10 code for megalencephalic leukoencephalopathy with subcortical cysts?

The ICD-10-CM code for megalencephalic leukoencephalopathy with subcortical cysts is G93.42 (sometimes written as G9342). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

Is G93.42 (Other and unspecified encephalopathy) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report megalencephalic leukoencephalopathy with subcortical cysts on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

What MS-DRG does G93.42 group to?

When megalencephalic leukoencephalopathy with subcortical cysts is the principal diagnosis on an inpatient stay, it groups to MS-DRG 974, 976, 72, 975, 70, 71, with relative weights from 0.7344 to 3.0488 depending on complications. Higher weights mean higher Medicare reimbursement.

Is G93.42 a CC or MCC?

CMS lists G93.42 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 9 closely related codes in its exclusion list.

What HCC is G93.42?

G93.42 (megalencephalic leukoencephalopathy with subcortical cysts) maps to CMS-HCC Category 200 (Friedreich and Other Hereditary Ataxias; Huntington Disease), commonly written as HCC 200, in the CMS-HCC V28 model used for Medicare Advantage risk adjustment in payment year 2027. It mapped to HCC 52 under the retired V24 model. It also maps in the ESRD (V21) and ESRD (V24) models. It does not map to any RxHCC in the Part D prescription drug model.

Does G93.42 risk-adjust for Medicare Advantage payment?

Yes. When documented and reported on a Medicare Advantage encounter, G93.42 adds a risk adjustment factor of about 0.279 to the beneficiary's RAF score for a community, non-dual, aged enrollee (published V28 weights range from 0.000 to 0.428 depending on the payment segment). HCC 200 sits at the top of its hierarchy, so no other condition category supersedes it. See the full factor table on the HCC 200 category page.