The patient: A 16-year-old girl in California

The symptoms: The teenager was referred to an emergency department because she was having hallucinations, including seeing a flying green dinosaur and hearing voices telling her to hurt others. She also had a sense that she was being followed.

In the emergency room, she was trembling and sweating and had a racing pulse and shallow, fast breathing. She did not have a fever, although she did have one at the hospital that had referred her.

During her conversations with ER clinicians, the teen reacted to the vision of the dinosaur as though the creature were present in the room. She reported that she had experienced these hallucinations since seventh grade,‬ so for about four years.

While her parents countered that she hadn’t exhibited psychotic symptoms until 48 hours before they arrived in the ER, they noted that her interest in school and extracurriculars had waned over the past month.

What happened next: Because of the patient's abnormal vital signs, the ER doctors suspected that her hallucinations might be secondary to some physical ailment, such as trauma to the brain, they wrote in a case report. However, a CT scan showed no signs of swelling or hemorrhage in her head. The doctors attempted a lumbar puncture (also called a spinal tap) but failed to collect any cerebrospinal fluid that they could test for irregularities.

The doctors judged the girl to be too medically unstable to be referred to the hospital's psychiatric ward, so she was admitted to the general pediatric department. Pediatric neurologists suggested an electroencephalogram (EEG), a test that measures electric signaling in the brain, but this revealed no further clues.

On her second day in the hospital, the girl entered a complete catatonic state. Her specific symptoms were not described in the report, but in general, catatonia disrupts how a person processes and reacts to the world around them. Catatonic patients often stop moving and speaking. Doctors treated the patient with lorazepam, which slows down nervous-system signaling, and her catatonia subsided in days.

Meanwhile, interventional radiologists performed a successful second lumbar puncture, but the girl's cerebrospinal fluid appeared normal in the initial panels they ran.

After the patient had spent eight days in the hospital, psychiatrists recommended that the girl be transferred to their ward. However, this was not possible because she developed problems with feeding herself. Her continued psychotic symptoms were treated with the antipsychotic drug olanzapine.

The diagnosis: While initial tests of the girl's cerebrospinal fluid did not show signs of meningitis or other abnormalities, a later test came back positive for autoantibodies — immune proteins that target healthy tissues instead of foreign invaders. These antibodies targeted neuronal intermediate filament (NIF), a protein that helps give nerve cells structural support.

Based on this finding, the patient was diagnosed with autoimmune encephalitis, a condition in which the body produces antibodies that attack nervous tissue, leading to harmful inflammation that can cause psychiatric symptoms.

Autoimmune encephalitis is often triggered by a tumor; proteins produced by the growth can resemble proteins within nervous tissue, and the immune system develops a harmful response against the latter while attempting to fight the tumor. The doctors performed MRIs and a PET scan to look for tumors, but they did not find any.

The treatment: The girl received intravenous infusions of a steroid to reduce inflammation, as well as immunoglobulin — antibodies from healthy donors that are often used to calm autoimmune reactions. She also got an infusion of rituximab, a drug that kills B lymphocytes, a type of white blood cell that makes antibodies like the ones attacking the girl's neurons.

In addition to these infusions, the girl underwent five sessions of plasmapheresis over the next month. In that procedure, blood is drawn from the body, a machine separates plasma (the liquid portion of blood) from blood cells, and the extracted plasma is substituted with a replacement fluid before that blood is returned to the patient. This treatment can help rid the body of autoantibodies.

The girl was discharged after having spent almost two months in the hospital. She was treated with ongoing prescriptions of olanzapine and lorazepam, as well as prednisone and monthly immunoglobulin treatments. As her symptoms improved over the following year, she stopped taking the psychiatric drugs but continued her immunotherapy.

What makes the case unique: Autoimmune encephalitis is rare. One study conducted in the U.K. suggests it affects only 5 to 8 out of every 100,000 people. Additionally, most data about the condition in pediatric patients comes from cases caused by autoantibodies that target NMDA receptors, which detect a key chemical messenger in the brain, rather than NIF.

The case report did not name a specific trigger for the girl's condition, but the authors noted that anti-NIF autoimmune encephalitis has been documented in adults following infections, including certain tick-borne bacterial infections, HIV and COVID-19. Cases associated with these infections are rarer than those linked to tumors.

The doctors did not attribute the teen's case to a specific infection, but her family did report that she'd had a cough three weeks before going to the emergency room. The family had visited the Philippines, and the girl and multiple relatives came down with the same illness.

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