G47.421 Narcolepsy in conditions classified elsewhere with cataplexy

Billable ICD-10-CM code, FY2026.

Applies from G47 Sleep disorders

Excludes2 (not included here)

• nightmares (F51.5)
• nonorganic sleep disorders (F51.-)
• sleep terrors (F51.4)
• sleepwalking (F51.3)

Applies from G47.42 Narcolepsy in conditions classified elsewhere

Code first

• underlying condition

Risk adjustment (HCC)

• RxHCC V08: HCC 355 — Narcolepsy and Cataplexy

MS-DRG index

Defines the logic of DRG(s) 091-093 in MDC 01.

Approximate ICD-9-CM (GEMs)

• 347.11 Narcolepsy in conditions classified elsewhere, with cataplexy

Medicare Code Edits (MCE v43.1 (April 2026))

• Manifestation codes as principal diagnosis: Manifestation codes describe the manifestation of an underlying disease, not the disease itself, and are not allowed as principal diagnosis.

Code annotations containing back-references to G47.421

Back-references to G47.4

• Type 2 Excludes: F51.1 Hypersomnia not due to a substance or known physiological condition ("narcolepsy (G47.4-)")

Back-references to G47

• Type 2 Excludes: F51 Sleep disorders not due to a substance or known physiological condition ("organic sleep disorders (G47.-)")

Diagnosis Index entries for G47.421

• Narcolepsy › in conditions classified elsewhere › with cataplexy

Nearby codes

• G47.4 Narcolepsy and cataplexy
• G47.41 Narcolepsy
• G47.411 Narcolepsy with cataplexy
• G47.419 Narcolepsy without cataplexy
• G47.42 Narcolepsy in conditions classified elsewhere
• G47.421 Narcolepsy in conditions classified elsewhere with cataplexy (this code)
• G47.429 Narcolepsy in conditions classified elsewhere without cataplexy
• G47.5 Parasomnia
• G47.50 Parasomnia, unspecified
• G47.51 Confusional arousals
• G47.52 REM sleep behavior disorder