ICD-10 Code G47.421 – Narcolepsy in conditions classified elsewhere with cataplexy (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code G47.421 – Narcolepsy in conditions classified elsewhere with cataplexy
What it is
This code identifies narcolepsy with cataplexy when the sleep disorder occurs as part of another underlying condition. Use it when documentation links the narcoleptic symptoms to a separate, known cause.
Clinical signs
Clinical features vary; refer to documentation. Typical findings include excessive daytime sleepiness, sudden sleep attacks, and cataplexy, which is brief muscle weakness triggered by emotion.
When to use this code
Use this code when the record states narcolepsy with cataplexy is secondary to another disease or condition. It may appear in neurology or sleep medicine notes when the provider documents an underlying cause and the sleep disorder together.
Confirm that cataplexy is present and that the diagnosis is not being coded as primary narcolepsy. If the source does not clearly identify the associated condition, check documentation.
Do not use for
Do not use this code for narcolepsy without cataplexy or when narcolepsy is documented as primary. Do not assume causation if the chart does not link the disorder to another condition.
Coding tip
Code the underlying condition first when documentation supports a causal relationship, and verify whether cataplexy is explicitly recorded.