ICD-10 Code G99 – Other disorders of nervous system in diseases classified elsewhere (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code G99 – Other disorders of nervous system in diseases classified elsewhere
What it is
G99 identifies nervous system disorders that are caused by another underlying disease and are not classified elsewhere. Use it when the neurologic problem is secondary to a documented condition.
Clinical signs
Clinical features vary; refer to documentation. Findings may include neurologic dysfunction linked to the underlying disease, such as weakness, sensory changes, or autonomic involvement.
When to use this code
Use G99 when the record clearly states a nervous system disorder due to another disease and no more specific code exists. It is appropriate for secondary neurologic conditions documented as “in diseases classified elsewhere.”
Code the underlying disease first when sequencing rules require it, and add G99 to identify the neurologic manifestation. Check documentation for the causal condition and the exact neurologic diagnosis.
Do not use for
Do not use G99 for primary neurologic diseases or for symptoms without a documented cause. Do not use it when a more specific code describes the condition.
Coding tip
Verify that the chart links the neurologic disorder to an underlying disease before assigning G99.