Postimmun ac dissem encphlts, myelitis and encephalomyelitis

This code represents an acute inflammatory demyelinating disease of the central nervous system (brain and/or spinal cord) that occurs as a rare adverse reaction following immunization. It is characterized by rapid onset of neurological symptoms such as altered mental status, seizures, focal neurological deficits, or paralysis. The condition is immune-mediated, triggered by the body's response to a vaccine.

Use this code when documentation clearly indicates a diagnosis of acute disseminated encephalomyelitis (ADEM), myelitis, or encephalomyelitis that developed after a recent vaccination. The physician's notes should explicitly link the neurological event to the immunization. This code is appropriate for both inpatient and outpatient settings when this specific diagnosis is confirmed.

• Ensure documentation specifies "postimmunization" to differentiate from other forms of ADEM.
• Always sequence this code as the primary diagnosis if it is the reason for the encounter.
• Code the specific vaccine administered (Z23.xx) as an additional diagnosis to provide further context.