ICD-10 Code M04.9 – Autoinflammatory Syndrome, Unspecified (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code M04.9 – Autoinflammatory syndrome, unspecified
What it is
M04.9 identifies an autoinflammatory syndrome when the record does not name a specific subtype. Use it for a recurrent inflammatory disorder driven by innate immune dysregulation, with the exact syndrome left unspecified.
Clinical signs
Clinical features vary; refer to documentation. Records may describe recurrent fever, inflammatory flares, rash, joint pain, or other systemic inflammatory findings, but you should code only when the provider documents an autoinflammatory syndrome.
When to use this code
Use M04.9 when the clinician diagnoses an autoinflammatory syndrome but does not identify a more specific condition in the note. It also fits when the chart confirms the disorder and the subtype is not available in the available documentation. Do not assume a specific hereditary or periodic fever syndrome without provider support.
Do not use for
Do not use this code for autoimmune diseases, infections, or fever of unknown origin unless the provider clearly documents an autoinflammatory syndrome. If a more specific autoinflammatory diagnosis is stated, code that condition instead.
Coding tip
Query for the exact syndrome name whenever the documentation says only “autoinflammatory disorder” or “periodic fever syndrome.”