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FY2027 ICD-10-CM reference

G40.842: KCNQ2-related epilepsy, not intractable, without status epilepticus

By the HCC Buddy Coding Team

The official ICD-10-CM descriptor is KCNQ2-related epilepsy, not intractable, without status epilepticus. The FY2027 annual edition starts October 1, 2026. Check the edition that applies to the encounter or inpatient discharge, including any April update.

Billable code. Verified against the official FY2027 order file.

CMS-HCC V28

  • HCC 201: Seizure Disorders and Convulsions · RAF 0.245, Community Non-Dual Aged (CNA)

Payment year 2027, 2026 dates of service. HCC from the CMS 2027 Initial ICD-10-CM Mappings; RAF from the CMS-HCC V28 relative factors. For 2027 dates of service, CMS has not yet published the payment year 2028 mappings.

CMS-HCC V24

Not used for payment year 2027 Medicare Advantage payment

ESRD

  • HCC 79: Seizure Disorders and Convulsions

Coefficient pending: payment year 2027 coefficients for this model are not yet verified, so no RAF is shown. Mapping: PY2026 CMS mapping; CMS 2027 initial file unchanged.

PACE

Source verification pending

RxHCC

  • HCC 164: Epilepsy and Other Seizure Disorders, Except Intractable Epilepsy

Coefficient pending: payment year 2027 coefficients for this model are not yet verified, so no RAF is shown. Mapping: PY2026 CMS mapping; CMS 2027 initial file unchanged.

HHS-HCC

  • HCC 120: Seizure Disorders and Convulsions

RAF not applicable: HHS-HCC weights vary by metal level. Mapping: HHS-HCC 2026 benefit year.

FY2027 Tabular instructions

Instructions below include applicable chapter, section and parent-code notes. Each note identifies where it appears in the official source.

Excludes2

certain conditions originating in the perinatal period (P04-P96)

Source: G00-G99 (chapter, inherited).

Excludes2

certain infectious and parasitic diseases (A00-B99)

Source: G00-G99 (chapter, inherited).

Excludes2

complications of pregnancy, childbirth and the puerperium (O00-O9A)

Source: G00-G99 (chapter, inherited).

Excludes2

congenital malformations, deformations, and chromosomal abnormalities (Q00-Q99)

Source: G00-G99 (chapter, inherited).

Excludes2

endocrine, nutritional and metabolic diseases (E00-E88)

Source: G00-G99 (chapter, inherited).

Excludes2

injury, poisoning and certain other consequences of external causes (S00-T88)

Source: G00-G99 (chapter, inherited).

Excludes2

neoplasms (C00-D49)

Source: G00-G99 (chapter, inherited).

Excludes2

symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified (R00-R94)

Source: G00-G99 (chapter, inherited).

Instructional note

the following terms are to be considered equivalent to intractable: pharmacoresistant (pharmacologically resistant), treatment resistant, refractory (medically) and poorly controlled

Source: G40 (category, inherited).

Excludes1

conversion disorder with seizures (F44.5)

Source: G40 (category, inherited).

Excludes1

convulsions NOS (R56.9)

Source: G40 (category, inherited).

Excludes1

post traumatic seizures (R56.1)

Source: G40 (category, inherited).

Excludes1

seizure (convulsive) NOS (R56.9)

Source: G40 (category, inherited).

Excludes1

seizure of newborn (P90)

Source: G40 (category, inherited).

Excludes2

hippocampal sclerosis (G93.81)

Source: G40 (category, inherited).

Excludes2

mesial temporal sclerosis (G93.81)

Source: G40 (category, inherited).

Excludes2

temporal sclerosis (G93.81)

Source: G40 (category, inherited).

Excludes2

Todd's paralysis (G83.84)

Source: G40 (category, inherited).

Instructional note

Epilepsies and epileptic syndromes undetermined as to whether they are focal or generalized

Source: G40.8 (self, inherited).

Instructional note

Landau-Kleffner syndrome

Source: G40.8 (self, inherited).

Instructional note

KCNQ2-related epilepsy NOS

Source: G40.842 (self, direct).

Source: CMS FY2027 Tabular List and Alphabetic Index.

Open Tabular instructions and code details

Compare the FY2027 additions, removals and billable-status changes

What does G40.842 mean in FY2027?

The official ICD-10-CM descriptor is KCNQ2-related epilepsy, not intractable, without status epilepticus. The FY2027 annual edition starts October 1, 2026. Check the edition that applies to the encounter or inpatient discharge, including any April update.

Is G40.842 billable in FY2027?

The FY2027 order file marks G40.842 as billable. Check the complete Tabular instructions and documentation before assigning it.

Does G40.842 map to an HCC?

In the CMS 2027 Initial ICD-10-CM Mappings (payment year 2027, 2026 dates of service), G40.842 maps to CMS-HCC V28 HCC 201 (Seizure Disorders and Convulsions). For 2027 dates of service, CMS has not yet published the payment year 2028 mappings. Under the PY2026 CMS mapping; CMS 2027 initial file unchanged: ESRD HCC 79; RxHCC HCC 164. Coefficients for these models are pending verification for payment year 2027. HHS-HCC: HCC 120 under the HHS-HCC 2026 benefit year mapping (no RAF; HHS-HCC weights vary by metal level). CMS-HCC V24: not used for payment year 2027 Medicare Advantage payment (CMS CY 2027 Rate Announcement). The PACE mapping is still pending verification for FY2027.

Source: CMS FY2027 ICD-10-CM order file. Payment model: CMS CY 2027 Rate Announcement. Read the FY2027 Official Guidelines.

Review the FY2026 April edition