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

Billing Status: YES. This is a valid, specific, and billable ICD-10-CM reference.

Coding at a Glance

Tabular directives
4 Excludes2
Risk adjustment
CMS-HCC V28: 1 category

Inpatient Payment Groups (MS-DRG)

Potential MS-DRG participation — not a DRG assignment.

MS-DRGs this diagnosis helps define, as principal or secondary, per the CMS ICD-10-CM/PCS MS-DRG Definitions Manual v44, Appendix B.

  • MS-DRG 070 — OTHER CEREBROVASCULAR DISORDERS WITH MCC (MDC 01)
  • MS-DRG 071 — OTHER CEREBROVASCULAR DISORDERS WITH CC (MDC 01)
  • MS-DRG 072 — OTHER CEREBROVASCULAR DISORDERS WITHOUT CC/MCC (MDC 01)
  • MS-DRG 974 — HIV WITH MAJOR RELATED CONDITION WITH MCC (MDC 25)
  • MS-DRG 975 — HIV WITH MAJOR RELATED CONDITION WITH CC (MDC 25)
  • MS-DRG 976 — HIV WITH MAJOR RELATED CONDITION WITHOUT CC/MCC (MDC 25)

A diagnosis appearing in a group's logic does not by itself determine the DRG assigned to a stay; the grouper uses the full claim.

Risk Adjustment (CMS-HCC)

Payment categories this diagnosis maps to under CMS-HCC V28, payment year 2026.

  • HCC 200 — Friedreich and Other Hereditary Ataxias; Huntington Disease

Risk scores depend on the enrollee's full accepted diagnosis set and segment; a category mapping alone does not determine payment.

Coding instructions

Official Tabular Instructional Notes: the inclusion, exclusion and sequencing notes published for G93.42 in the official ICD-10-CM tabular list, quoted as published.

Source: CMS/CDC — ICD-10-CM Tabular ListRelease: FY2027Effective: October 1, 2026

Trace:FY2027 changesChange historyRelease, file and checksum

Notes without a marker are published on G93.42 itself; “inherited from” names the category or block whose note applies here.

Excludes2 — Not Included Here

Conditions not covered by this code, but which may be reported alongside it when both are present.

Source: inherited from G93.4

Coder workflow for G93.42

MedCoder structured workflow — derived from this code’s own official record

Before you code G93.42

  1. G93.42’s title joins a condition with an associated condition or complication. Confirm each component is documented. Where the classification presumes the link through the “with” convention, only a provider statement that the conditions are unrelated defeats it. A combination code is assigned only when it fully identifies the documented conditions; a required second code for the stage, type or manifestation is still reported when the notes ask for it (Guidelines I.B.9, I.A.15).

    Guide: Combination codes →

Documentation check

The provider’s diagnostic statement
Codes are assigned from the provider’s documented diagnosis, not from clinical criteria, test values or a medication list (Guidelines I.A.19).
The associated condition or complication
Whether the associated condition the title names is documented; the “with” convention presumes some links, and a provider statement that the conditions are unrelated defeats it (Guidelines I.A.15).

Official instructions as workflow

  • Excludes2 — not part of G93.42(4 notes)

    Coding workflow: The conditions named in this note are not included in G93.42. When the record documents both, both may be reported; the note is a boundary, not a prohibition.

    CompareG31.2, G94, I67.4, G92.8

    See the official tabular notes · Guidelines I.A.12.b

Coding decision scenarios

Pattern scenarios for this code’s structure — decision rules, not clinical cases

Documentation: Only one of the components this code’s title joins is documented.

Coding question: Is G93.42 supported?

Path: Review the code for the documented component on its own.

Reason: A combination code is assigned only when it fully identifies the documented conditions; otherwise the documented component takes its own code (Guidelines I.B.9).

Every row is derived from this code’s own record — its title, tabular notes, 7th-character family and same-category siblings — with fixed MedCoder wording; nothing is inferred about a patient. The official notes and guideline text are in the sections each row links to, and they control.

Don’t confuse G93.42 with…

MedCoder analysis — pairs from this code’s official notes, distinctions written by MedCoder

The codes most likely to be picked instead of G93.42 — named in its own official notes, or sharing its laterality or encounter family — with what separates them and which documentation moves the case. Each links to the full comparison.

  • G93.40— Specificity relationship (Review)

    Overlapping diagnoses in the same category.

    Overlapping codes in the same category — the documentation decides which is the more specific fit.

    What moves you there: A record that documents no more than “Encephalopathy, unspecified” takes G93.40; specificity in the record moves it back here.

    Full comparison: G93.42 vs G93.40 →

  • G31.2— Excludes2 relationship (Informational)

    Distinct conditions — both may be reported.

    A distinct condition — both may be reported when both are documented.

    What moves you there: Documentation of alcoholic encephalopathy adds G31.2; it is not part of this code and both may be reported when both are documented.

    Full comparison: G93.42 vs G31.2 →

  • G94— Excludes2 relationship (Informational)

    Distinct conditions — both may be reported.

    A distinct condition — both may be reported when both are documented.

    What moves you there: Documentation of encephalopathy in diseases classified elsewhere adds G94; it is not part of this code and both may be reported when both are documented.

    Full comparison: G93.42 vs G94 →

  • I67.4— Excludes2 relationship (Informational)

    Distinct conditions — both may be reported.

    A distinct condition — both may be reported when both are documented.

    What moves you there: Documentation of hypertensive encephalopathy adds I67.4; it is not part of this code and both may be reported when both are documented.

    Full comparison: G93.42 vs I67.4 →

  • G92.8— Excludes2 relationship (Informational)

    Distinct conditions — both may be reported.

    A distinct condition — both may be reported when both are documented.

    What moves you there: Documentation of toxic (metabolic) encephalopathy adds G92.8; it is not part of this code and both may be reported when both are documented.

    Full comparison: G93.42 vs G92.8 →

Relationships are read from this code's own official notes, its laterality siblings and its encounter family; the wording of each distinction is MedCoder editorial, and the documentation named in each “what moves you there” line is the official note phrase or sibling title itself. Source: CMS ICD-10-CM tabular instructional notes; ICD-10-CM Official Guidelines, Section I.A.12.a.

Code Overview

Megalencephalic leukoencephalopathy with subcortical cysts is a billable ICD-10-CM diagnosis code (G93.42).

MedCoder summary Summary composed by MedCoder from this code's official ICD-10-CM record. The tabular instructional notes themselves appear verbatim below.

Indexed Clinical Terms (1)

Official source data — entries quoted as published, in the Index’s own lookup phrasing

Clinical term phrases from the official ICD-10-CM Index to Diseases and Injuries that map to this code. These are alphabetic-index entries shown as the Index writes them — lookup phrasing, not necessarily the wording of a final diagnosis.

Verify Before Coding

  • CC as a secondary diagnosis (FY2027). Can raise the stay's MS-DRG severity tier.

From the code registry, the Medicare Code Editor, and the MS-DRG Definitions Manual. Check it against a full claim in Claim Check.

Relationships & Classification

MedCoder structured relationships — computed from published CMS and AHRQ datasets

Other codes that name G93.42 or its code family, from the CMS ICD-10-CM tabular instructional notes. Tabular-note edges are stored at the code family level that carries each note.

Referenced by 1 Code Also instruction: F78.A1 — SYNGAP1-related intellectual disability (via G93.4.-).

These codes suggest coding this condition alongside when both are present.

MS-DRG Grouper Relationships (FY2027)

Potential MS-DRG participation — not a DRG assignment.

FY2027 MS-DRG: CC — Complication or Comorbidity. Reported as a secondary diagnosis, this code raises the stay's MS-DRG severity tier — except when the principal diagnosis is one of 9 clinically related codes on its CMS exclusion list. Does not count toward severity when the stay groups to DRGs 974-976 (HIV with Major Related Condition).

Named in the grouper logic of 6 MS-DRGs: DRG 070 (MDC 01), DRG 071 (MDC 01), DRG 072 (MDC 01), DRG 974 (MDC 25), DRG 975 (MDC 25), DRG 976 (MDC 25).

From the CMS MS-DRG Definitions Manual (Appendices B and C). Actual DRG assignment depends on the complete claim.

Clinical classification (AHRQ CCSR):NVS006 — Other nervous system disorders (often hereditary or degenerative) (default).

Clinical Classifications Software Refined (CCSR) for ICD-10-CM Diagnoses. Healthcare Cost and Utilization Project (HCUP), Agency for Healthcare Research and Quality.

Related Codes

Same clinical process (MS-DRG)

Acts as CC — raises the severity of other admissions. CMS groups these diagnoses into one MS-DRG principal-diagnosis exclusion process — a CC/MCC on this list never raises severity when the principal diagnosis is also on it.

G21.0 — Malignant neuroleptic syndrome, G83.5 — Locked-in state, G93.40 — Encephalopathy, unspecified, G93.41 — Metabolic encephalopathy, G93.43 — Leukoencephalopathy with calcifications and cysts, G93.44 — Adult-onset leukodystrophy with axonal spheroids, G93.45 — Developmental and epileptic encephalopathy, G93.49 — Other encephalopathy

Same CMS-HCC risk category (V28)

CMS maps these diagnoses to the same Hierarchical Condition Category (Friedreich and Other Hereditary Ataxias; Huntington Disease) for risk-adjusted payment.

G10 — Huntington's disease, G11.0 — Congenital nonprogressive ataxia, G11.10 — Early-onset cerebellar ataxia, unspecified, G11.11 — Friedreich ataxia, G11.19 — Other early-onset cerebellar ataxia, G11.2 — Late-onset cerebellar ataxia, G11.3 — Cerebellar ataxia with defective DNA repair, G11.4 — Hereditary spastic paraplegia, G11.5 — Hypomyelination - hypogonadotropic hypogonadism - hypodontia, G11.6 — Leukodystrophy with vanishing white matter disease, G11.8 — Other hereditary ataxias, G11.9 — Hereditary ataxia, unspecified, G31.80 — Leukodystrophy, unspecified, G90.B — LMNB1-related autosomal dominant leukodystrophy, G93.43 — Leukoencephalopathy with calcifications and cysts, G93.44 — Adult-onset leukodystrophy with axonal spheroids

Same clinical category (CCSR)

AHRQ's Clinical Classifications Software groups these diagnoses under the same clinical category (Other nervous system disorders (often hereditary or degenerative)).

G31.84 — Mild cognitive impairment of uncertain or unknown etiology, G31.85 — Corticobasal degeneration, G31.86 — Alexander disease, G31.87 — Primary progressive apraxia of speech, G31.89 — Other specified degenerative diseases of nervous system, G31.9 — Degenerative disease of nervous system, unspecified, G32.0 — Subacute combined degeneration of spinal cord in diseases classified elsewhere, G32.81 — Cerebellar ataxia in diseases classified elsewhere, G32.89 — Other specified degenerative disorders of nervous system in diseases classified elsewhere, G90.01 — Carotid sinus syncope, G90.09 — Other idiopathic peripheral autonomic neuropathy, G90.1 — Familial dysautonomia [Riley-Day], G90.3 — Multi-system degeneration of the autonomic nervous system, G90.4 — Autonomic dysreflexia, G90.B — LMNB1-related autosomal dominant leukodystrophy, G93.43 — Leukoencephalopathy with calcifications and cysts, G93.44 — Adult-onset leukodystrophy with axonal spheroids, G93.45 — Developmental and epileptic encephalopathy, G99.0 — Autonomic neuropathy in diseases classified elsewhere, G99.2 — Myelopathy in diseases classified elsewhere, +83 more

Same Index main term, other category

The ICD-10-CM Index to Diseases and Injuries files this code under the main term “Leukoencephalopathy”; these codes share that main term but sit in a different category of the Tabular List.

A81.1 — Subacute sclerosing panencephalitis (van Bogaert's), A81.2 — Progressive multifocal leukoencephalopathy (multifocal), E75.25 — Metachromatic leukodystrophy (metachromatic), E88.43 — Disorders of mitochondrial tRNA synthetases (with, thalamus - brainstem involvement - high lactate), G04.02 — Postimmunization acute disseminated encephalitis, myelitis and encephalomyelitis (postimmunization and postvaccinal), G92.8 — Other toxic encephalopathy (heroin vapor), I67.3 — Progressive vascular leukoencephalopathy (Binswanger's)

Lab tests where this diagnosis supports Medicare coverage (NCD)

Medicare's National Coverage Determination (NCD) program lists this diagnosis as medical justification for these lab tests.

HIV Screening Test

Contextual Map

Every relationship of G93.42 in one view: hierarchy, official tabular instructions in both directions, clinical classification, risk adjustment, MS-DRG participation, index terms and change history — each edge carrying the CMS source it derives from.

Run G93.42 with this related code in Claim Check

Hierarchy

Referenced by Code Also instructions

Clinical classification (CCSR)

Risk adjustment (CMS-HCC)

  • HCC 200 — Friedreich and Other Hereditary Ataxias; Huntington Disease [CMS-HCC]— CMS-HCC V28 · 2026

MS-DRG Grouper

MDC crossing

  • MDC 01 — Diseases and Disorders of the Nervous System[MDC crossing]: “Diseases and Disorders of the Nervous System — the grouper's crossing between diagnoses and procedures: a principal diagnosis sets the MDC, and same-MDC procedures move the stay to its surgical DRGs. 8,919 same-MDC procedures group here; browse them on the MDC page.”— CMS MS-DRG Definitions Manual · FY2027
  • MDC 25 — Human Immunodeficiency Virus Infections[MDC crossing]: “Human Immunodeficiency Virus Infections — the grouper's crossing between diagnoses and procedures: a principal diagnosis sets the MDC, and same-MDC procedures move the stay to its surgical DRGs.”— CMS MS-DRG Definitions Manual · FY2027

Index entries

  • Leukoencephalopathy, megalencephalic, with subcortical cysts[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026

Nearest codes (23)

Change history (3)

Sources for this page

Codes, titles, notes, index terms and mappings on this page are transcribed from the datasets below. Relationships MedCoder computed and text MedCoder wrote are labelled where they appear.

Code, title, tabular notes and index terms Official source data
CMS/CDC ICD-10-CM FY2027 tabular list, index and tables, effective October 1, 2026 Release, file and checksum · Publisher’s page
Claim edits Official source data
CMS Definitions of Medicare Code Edits — v44.0 (October 2026) Release, file and checksum · Publisher’s page
Inpatient payment groups Official source data
CMS MS-DRG Definitions Manual (incl. Appendix B diagnosis index, Appendix C CC/MCC list, Appendix E procedure index) and IPPS Final Rule tables — v44 Release, file and checksum · Publisher’s page
Risk adjustment Official source data
2026 Mid-Year Final ICD-10 Mappings + Model Software (cms.gov/files/zip/2026-midyear-final-icd-10-mappings.zip, 2026-midyear-final-model-software.zip) — CMS-HCC V28, PY2026 mid-year final release Release, file and checksum · Publisher’s page
Change history and date-of-service validity Official source data
CMS ICD-10-CM release addenda, ingested release by release into the change ledger Release, file and checksum · Publisher’s page
Comparisons, relationships and the contextual map MedCoder structured relationship
Computed by MedCoder from the tabular notes and tables above; every derived relationship is marked as derived where it appears
Summary and FAQ answers MedCoder explanation
Written by MedCoder to explain the sources above: drafted with AI assistance, checked by a person against the release files, and labelled as MedCoder text where it appears. Not official text.

Labels on this page: Official source data · MedCoder structured relationship · MedCoder explanation. How to read the labels · All data sources and release dates

Cite this page

Reference this page in a research guide, syllabus or article. The release is included because code content changes each year.

MedCoder.ai. "G93.42 — Megalencephalic leukoencephalopathy with subcortical cysts." ICD-10-CM FY2027. https://medcoder.ai/icd10/code/g93.42-megalencephalic-leukoencephalopathy-with-subcortical-cysts

Change history

  • FY2025 — October 1, 2024
    Description revised
    Megaloencephalic leukoencephalopathy with subcortical cysts → Megalencephalic leukoencephalopathy with subcortical cysts
    FY2025 changes
  • FY2025 — October 1, 2024
    Short description revised
    Megaloencephalic leukoencephalopathy with subcortical cysts → Megalencephalic leukoencephalopathy with subcortical cysts
    FY2025 changes
  • FY2024 — October 1, 2023
    Added to the code set
    Megaloencephalic leukoencephalopathy with subcortical cysts
    FY2024 changes

Nearest Codes in This Family

Official ICD-10-CM classifications closest to G93.42 in its code family, with their registry titles.

View all codes in the G93 family