NMDA-receptor encephalitis in Denmark from 2009 to 2019: a national cohort study

Mette Scheller Nissen*, Maren Synnøve Ørvik, Anna Christine Nilsson, Matias Ryding, Magnus Lydolph, Morten Blaabjerg

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review


Background: To describe the national Danish N-methyl-d-aspartate receptor encephalitis (NMDARE) cohort. Methods: All NMDAR immunoglobulin G (IgG) positive cases in Denmark from 2009 to 2019 were included. Medical information was assessed retrospectively for clinical phenotype, workup, treatment and outcome. Results: Seventy-seven patients were NMDAR IgG positive in serum/CSF. Fifty-five fulfilled the criteria of NMDARE, 18 did not and 4 had missing data. Incidence was 0.17/100,000 persons per year in 2018, and incidence rates increased since 2009. Of the 55 NMDARE patients (median age 27; 60% female), 9 had post-herpes simplex (HSE) NMDARE and 7 had a tumor (four teratomas). MRI was normal in 51% of patients. Brain FDG PET was performed in 17 patients, and was abnormal in 47% of patients with a normal MRI. First-line therapy was administered to 91%, and 24% required second-line therapy. Maintenance therapy during recovery was given 84% of patients, with no effect on relapse-risk. ICU admission occurred in 29%. Poor outcome (mRS > 2) was reported in 27% and dependent on age and etiology. Patients > 45 years had a poorer outcome (71% vs 8%, p < 0.0001), more frequently post-HSE NMDARE (47% vs 3%, p < 0.0001) and underlying malignancies (18% vs 0%). Conclusion: The incidence of NMDARE in Denmark is currently 0.17/100,000 persons per year, and has increased since 2009. NMDARE patients in Denmark display a higher median age, lower female:male ratio, a less frequent tumor association and need for ICU admission. Maintenance therapy did not reduce relapse rate. Poor outcome was seen with higher age, likely related to underlying etiology.

Original languageEnglish
JournalJournal of Neurology
Issue number3
Pages (from-to)1618-1630
Publication statusPublished - Mar 2022


  • Anti-N-methyl-d-aspartate receptor encephalitis
  • Autoimmune encephalitis
  • Cohort studies
  • NMDA-receptor
  • Post-herpes simplex virus 1 encephalitis
  • Humans
  • Neoplasm Recurrence, Local
  • Male
  • Receptors, N-Methyl-D-Aspartate
  • Anti-N-Methyl-D-Aspartate Receptor Encephalitis/therapy
  • Denmark/epidemiology
  • Adult
  • Female
  • N-Methylaspartate
  • Retrospective Studies
  • Cohort Studies


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