Psychosis and seizures in a young woman. An ovarian teratoma was triggering autoimmunity.

A sudden shift

In late November 2025, a previously healthy 20-year-old Hispanic woman experienced a sudden onset of progressive behavioral changes. Within one week, she was struggling with anxiety, insomnia, and mood lability. The situation quickly escalated beyond emotional distress as she developed focal seizures, dysarthria (slurred speech), and a fluctuating level of consciousness.

What looked psychiatric

When she was admitted to Hospital Médica Sur in Mexico City on December 8, she was awake but disoriented. Her speech was incoherent and dysarthric. While her initial symptoms resembled a primary psychiatric breakdown, objective physical signs suggested a more systemic crisis: she was tachycardic with a heart rate of 131 bpm and hypertensive at 149/91 mmHg.

Neurological examination revealed orofacial dyskinesias—involuntary movements of the face and mouth—along with hyperreflexia, increased muscle tone, and weakness in her right arm. Her attention fluctuated markedly, a sign of acute encephalopathy rather than a typical psychiatric disorder.

Searching for a cause

Initial tests did not provide immediate answers. A brain MRI showed no structural abnormalities, neoplasms, or vascular lesions. A lumbar puncture revealed only mild inflammatory changes, with a slightly elevated white blood cell count of 11 cells/mm³ in the cerebrospinal fluid. Multiple infectious PCR panels for viruses and bacteria came back negative.

An EEG showed diffuse slowing of brain waves, a pattern indicating moderate-to-severe cortical dysfunction. While her mother revealed she had a known 2 cm ovarian cyst being monitored with oral contraceptives, a new pelvic MRI showed the mass had grown significantly to 11 x 14 x 5.4 cm. It was identified as a mature cystic teratoma.

The autoimmune link

The medical team suspected anti-NMDA receptor encephalitis, a condition where the body’s immune system attacks the brain. In many young women, this is triggered by a teratoma containing neural tissue that expresses NMDA receptors, essentially "training" the immune system to attack that same receptor in the brain.

Because antibody testing required shipping samples to the Mayo Clinic with a 10- to 14-day wait time, the team decided not to wait for confirmation. Based on high clinical suspicion, they initiated high-dose steroids and plasma exchange.

Treatment and recovery

On her third day in the ICU, the patient underwent "ultra-early" surgery to remove the left ovary and the 614-gram tumor. This was considered a "disease-modifying intervention" to remove the source of the autoimmune trigger. Following surgery, she received intravenous immunoglobulin and rituximab to further suppress the rogue immune response.

The strategy worked. On day 14 of her stay, the anti-NMDA receptor antibody test finally returned positive, confirming the diagnosis. By the time she was discharged five weeks later, she was alert, oriented, and able to walk with minimal assistance. After three months of follow-up, she had nearly fully recovered, with only minimal residual weakness in her arms.