ICD-10 Code G99.8 – Other specified disorders of nervous system in diseases classified elsewhere (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code G99.8 – Other specified disorders of nervous system in diseases classified elsewhere
What it is
G99.8 is used for a nervous system disorder caused by another disease, when the documentation identifies a specific “other specified” neurologic condition not captured by a more exact code. It is an etiology-related code, so you must also code the underlying disease.
Clinical signs
Clinical features vary; refer to documentation. You may see neurologic findings linked to a known underlying disorder, such as weakness, abnormal movement, sensory changes, or autonomic symptoms, but the record must support the specific nervous system involvement.
When to use this code
Use G99.8 when the provider documents a nervous system disorder due to another condition and no more specific ICD-10-CM code fits. It is appropriate when the chart identifies the neurologic manifestation but does not name a better-defined code. Code the causative disease first when required by guideline.
Do not use for
Do not use this code for unspecified nervous system disorders without an underlying disease, or when a more specific neurologic code is available. Check documentation if the condition is better described by a separate manifestation code.
Coding tip
Always confirm the underlying disease and the exact neurologic manifestation, then sequence both codes according to the documentation.