2026 ICD-10-CM Diagnosis Code G47.421Narcolepsy in conditions classified elsewhere with cataplexy

ICD-10-CM Codes›G00–G99›G40-G47›G47

ICD-10-CM G47.421
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

G47.421 is a billable ICD-10-CM diagnosis code for narcolepsy in conditions classified elsewhere with cataplexy. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026). The code is a manifestation code that cannot be reported as the principal diagnosis. Coders also document this condition as narcolepsy. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Sleep wake disorders.

Code Identity

ICD-10-CM Code
G47.421
Billable Status
Yes — Valid for Submission
Code Describes
Narcolepsy in conditions classified elsewhere with cataplexy
Short Description
Narcolepsy in conditions classified elsewhere with cataplexy
Same as the full description in the CMS dataset.
Parent Code
G47.42
Narcolepsy in conditions classified elsewhere

Code Classification

ChapterG00–G99Diseases of the nervous system
SectionG40-G47Episodic and paroxysmal disorders
CategoryG47Sleep disorders
This CodeG47.421Narcolepsy in conditions classified elsewhere with cataplexy

Code EditsBilling

Medicare Code Editor checks that affect claim validity for G47.421.

Manifestation diagnoses
Manifestation codes describe the manifestation of an underlying disease, not the disease itself, and therefore should not be used as a principal diagnosis.

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Narcolepsy
  • Primary hypersomnia
  • Secondary narcolepsy
  • Secondary narcolepsy with cataplexy

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

External Cause of Injuries IndexGuidance

References for this code in the External Cause of Injuries Index.

    • Narcolepsy
      • in conditions classified elsewhere
        • with cataplexy

Clinical ClassificationClinical

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

CCSR NVS016
Sleep wake disorders
Default principal diagnosis: inpatient No · outpatient No

Clinical InformationClinical

  • Narcolepsy

    a condition characterized by recurrent episodes of daytime somnolence and lapses in consciousness (microsomnias) that may be associated with automatic behaviors and amnesia. cataplexy; sleep paralysis, and hypnagogic hallucinations frequently accompany narcolepsy. the pathophysiology of this disorder includes sleep-onset rapid eye movement (rem) sleep, which normally follows stage iii or iv sleep. (from neurology 1998 feb;50(2 suppl 1):s2-s7)

  • Narcolepsy

    a sleep disorder characterized by a tendency for excessive sleepiness during the day which occurs even after adequate sleep in the nighttime. the persons who suffer from this condition experience fatigue and may fall asleep at inappropriate times during the day.

  • Narcolepsy in Conditions Classified Elsewhere with Cataplexy|Narcolepsy in conditions classified elsewhere with cataplexy

    evidence of narcolepsy in conditions classified elsewhere with cataplexy.

  • Narcolepsy in Conditions Classified Elsewhere without Cataplexy|Narcolepsy in conditions classified elsewhere without cataplexy

    evidence of narcolepsy in conditions classified elsewhere without cataplexy.

  • Narcolepsy with Cataplexy|Narcolepsy with cataplexy

    evidence of narcolepsy with cataplexy.

  • Narcolepsy without Cataplexy|Narcolepsy without cataplexy

    evidence of narcolepsy without cataplexy.

Patient EducationClinical

Sleep Disorders

Sleep is a complex biological process. While you are sleeping, you are unconscious, but your brain and body functions are still active. They are doing a number of important jobs that help you stay healthy and function at your best. So when you don't get enough quality sleep, it does more than just make you feel tired.

The full article covers:

  • What is sleep?
  • What are sleep disorders?
  • What causes sleep disorders?
  • What are the symptoms of sleep disorders?
  • How are sleep disorders diagnosed?
  • What are the treatments for sleep disorders?

Read the full article at MedlinePlus

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

Convert G47.421 to ICD-9-CMHistory

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

ICD-9-CM
347.11 Narcolepsy w cat oth dis
Exact Match The mapping is direct, with no qualifiers.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About G47.421Overview

Is G47.421 (Narcolepsy in conditions classified elsewhere) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report narcolepsy in conditions classified elsewhere with cataplexy on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

Can G47.421 be a principal diagnosis?

No. This is a manifestation code: narcolepsy in conditions classified elsewhere with cataplexy describes the manifestation of an underlying disease rather than the disease itself, so the underlying condition is sequenced first.

What is the ICD-9 equivalent of G47.421?

Under the General Equivalence Mappings, narcolepsy in conditions classified elsewhere with cataplexy converts to ICD-9-CM 347.11 (narcolepsy w cat oth dis). The mapping is a direct match.

Footnotes

[1] Chronic - a chronic condition code indicates a condition lasting 12 months or longer and its effect on the patient based on one or both of the following criteria:

  • The condition results in the need for ongoing intervention with medical products,treatment, services, and special equipment
  • The condition places limitations on self-care, independent living, and social interactions.