G04.02Postimmunization acute disseminated encephalitis, myelitis and encephalomyelitis

G04.02 is the ICD-10-CM diagnosis code for Postimmunization acute disseminated encephalitis, myelitis and encephalomyelitis. It belongs to category G04 (encephalitis, myelitis and encephalomyelitis), block G00-G09 (inflammatory diseases of the central nervous system) and chapter 6 (diseases of the nervous system). It is billable, so it can be reported on its own for dates of service from October 1, 2026 through September 30, 2027.

Within G04.0 (acute disseminated encephalitis and encephalomyelitis (ADEM)), G04.02 is specifically for Postimmunization acute disseminated encephalitis, myelitis and encephalomyelitis. Related codes cover acute disseminated encephalitis and encephalomyelitis, unspecified (G04.00) and postinfectious acute disseminated encephalitis and encephalomyelitis (postinfectious ADEM) (G04.01).

Use an additional code to identify the vaccine (T50.A-, T50.B-, T50.Z-).

As a secondary diagnosis it is an MCC (major complication or comorbidity), which can move an inpatient stay into the highest-paying "with MCC" MS-DRG of its family, unless the principal diagnosis excludes it.

In MS-DRG v44.0, it is part of the grouping logic for DRG 023 (Craniotomy with Major Device Implant or Acute Complex CNS Principal Diagnosis with MCC or Antineoplastic Implant or Epilepsy with Neurostimulator, relative weight 5.7444), DRG 024 (Craniotomy with Major Device Implant or Acute Complex CNS Principal Diagnosis without MCC, relative weight 3.9708), DRG 097 (Non-Bacterial Infection of Nervous System Except Viral Meningitis with MCC, relative weight 3.8226), DRG 098 (Non-Bacterial Infection of Nervous System Except Viral Meningitis with CC, relative weight 2.2706) and DRG 099 (Non-Bacterial Infection of Nervous System Except Viral Meningitis without CC/MCC, relative weight 1.5256), in MDC 01 (Diseases and Disorders of the Nervous System), as a principal or secondary diagnosis. The DRG a claim lands in depends on the principal diagnosis, procedures and any CC/MCC secondary diagnoses.

It has been part of ICD-10-CM since the code set took effect on October 1, 2015 and hasn't changed since.

Before ICD-10, this condition was coded in ICD-9-CM as 323.51 (encephalitis and encephalomyelitis following immunization procedures) and 323.52 (myelitis following immunization procedures).