MDLinxThis Rare Autoimmune Disease Masqueraded as Mental Illness—Would You Have Seen It? 

🧩 Diagnostic Reasoning Exercise / Teaching Case

Nora Scott presented with insomnia, racing thoughts, and manic episodes — a picture consistent with bipolar disorder. Four years into that diagnosis, progressive confusion, disorientation, loss of bodily control, and memory loss emerged. Two months of inpatient psychiatric treatment produced no improvement. A neurology consult changed everything.

Diagnostic Considerations

• Anti-NMDAR encephalitis presents with a psychiatric prodrome — psychosis, behavioral change, mood instability — before neurological symptoms emerge, making early psychiatric misdiagnosis common
• The condition is most commonly triggered by ovarian or extraovarian teratomas in women aged 12 to 45; carcinomas predominate in older patients; herpes simplex encephalitis accounts for a significant subset
• 27% of herpes encephalitis patients develop autoimmune encephalitis within 2 to 16 weeks post-infection; 64% of those cases involve anti-NMDAr antibodies
• Confirmation requires multimodal workup; empiric immunotherapy should not be withheld pending antibody results when clinical suspicion is high

Practice Pearls

• Recognize atypical trajectory: psychiatric symptoms that fail to follow expected patterns or worsen despite treatment warrant neurological reassessment
• Consider anti-NMDAR encephalitis in patients presenting with new-onset psychosis plus progressive neurological features, regardless of prior psychiatric history
• Integrate tumor screening and CSF analysis early; delayed diagnosis prolongs exposure to ineffective psychiatric treatment
• Initiate empiric immunotherapy when clinical suspicion is high rather than awaiting confirmatory antibody results