Short answer · Medically reviewed summary · Last updated: 2026-05-08
Anti-NMDA receptor encephalitis does not have a unique, dedicated ICD-10 or ICD-9 code; instead, it is classified under broader categories for encephalitis and autoimmune conditions. In the ICD-10 system, it is most commonly coded as G04.81 (Postencephalitic encephalitis and encephalomyelitis) or G04.90 (Encephalitis, unspecified), while in ICD-9, it was typically categorized under 323.81 (Other causes of encephalitis). Why is there no specific ICD code for Anti-NMDA receptor encephalitis? Because Anti-NMDA receptor encephalitis is a relatively recently characterized autoimmune disorder (first described in 2007), standard medical coding systems have not yet assigned a unique identifier.
ICD10 code of Anti-NMDA Receptor Encephalitis and ICD9 code
ICD-10 and ICD-9 codes for Anti-NMDA Receptor Encephalitis, with classification details for clinicians, coders and patients.
Anti-NMDA receptor encephalitis does not have a unique, dedicated ICD-10 or ICD-9 code; instead, it is classified under broader categories for encephalitis and autoimmune conditions. In the ICD-10 system, it is most commonly coded as G04.81 (Postencephalitic encephalitis and encephalomyelitis) or G04.90 (Encephalitis, unspecified), while in ICD-9, it was typically categorized under 323.81 (Other causes of encephalitis).
Why is there no specific ICD code for Anti-NMDA receptor encephalitis?
Because Anti-NMDA receptor encephalitis is a relatively recently characterized autoimmune disorder (first described in 2007), standard medical coding systems have not yet assigned a unique identifier. Clinicians often use secondary codes to specify the underlying mechanism, such as D89.89 (Other specified disorders involving the immune mechanism) to capture the autoimmune nature of Anti-NMDA receptor encephalitis.
How is the diagnosis of Anti-NMDA receptor encephalitis confirmed?
Diagnosis relies on the detection of IgG antibodies against the GluN1 subunit of the NMDA receptor in the cerebrospinal fluid (CSF). The clinical presentation of Anti-NMDA receptor encephalitis is distinct and often follows a predictable, albeit severe, progression. Key clinical features include:
- Psychiatric symptoms (agitation, psychosis, or catatonia)
- Seizures and movement disorders (often orofacial dyskinesias)
- Autonomic instability and hypoventilation
- Decreased level of consciousness
Is Anti-NMDA receptor encephalitis linked to other conditions?
In approximately 50% of adult female cases, Anti-NMDA receptor encephalitis is associated with an underlying paraneoplastic process, most commonly an ovarian teratoma. Early identification of these tumors is critical for effective treatment. At DiseaseMaps.org, 76 people with Anti-NMDA receptor encephalitis have joined our community, sharing their diverse experiences with diagnosis, treatment, and recovery, which can be a vital resource for those navigating this complex journey.
Next steps
- Consult a neuroimmunologist or a specialized neurologist to confirm the diagnosis through CSF antibody testing.
- If Anti-NMDA receptor encephalitis is suspected, ensure rapid screening for potential tumors (e.g., pelvic MRI or ultrasound).
- Connect with the 76 members in the DiseaseMaps community to share experiences and find emotional support.
- Work with a multidisciplinary team including physical, occupational, and speech therapists for post-acute rehabilitation.
Medical disclaimer: This information is for educational purposes only and does not replace professional medical advice, diagnosis, or treatment; always seek the advice of your physician regarding any medical condition.
References
- NIH Genetic and Rare Diseases Information Center (GARD)
- Orphanet (ORPHA: 209931)
- The Encephalitis Society
- Autoimmune Encephalitis Alliance
