ICD-10 Code G47.42 – Narcolepsy in conditions classified elsewhere (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code G47.42 – Narcolepsy in conditions classified elsewhere
What it is
This code identifies narcolepsy that is documented as occurring secondary to another condition. Use it when the chart clearly links the narcolepsy to an underlying disorder rather than primary narcolepsy.
Clinical signs
Clinical features vary; refer to documentation. Typical narcolepsy findings include excessive daytime sleepiness, sudden sleep attacks, and possible cataplexy, sleep paralysis, or hallucinations.
When to use this code
Use G47.42 when the provider states narcolepsy is due to, or occurs in the setting of, another condition. The underlying cause should also be documented and coded when applicable. If the record does not support a secondary relationship, check documentation.
Do not use for
Do not use this code for primary narcolepsy without an identified underlying condition. Do not assign it when the note only mentions daytime sleepiness or another sleep disorder without narcolepsy.
Coding tip
Look for explicit wording such as “due to,” “secondary to,” or “in conditions classified elsewhere” before assigning G47.42.