Spanish neuroscientist Josep Dalmau identified 11 autoimmune encephalitis types masquerading as psychiatric disorders

Most researchers spend their entire careers without discovering a single disease. Josep Dalmau has identified more than a dozen. The Spanish neuroimmunologist, born in Sabadell in 1953, now directs the Experimental Neuroimmunology Group at IDIBAPS and the CaixaResearch Institute in Barcelona, but much of his career unfolded in the United States, where he worked as a neuro-oncologist at Memorial Sloan Kettering in New York before moving to the University of Pennsylvania. In 2007, he identified the first autoimmune encephalitis—a devastating inflammatory disease in which the immune system mistakenly attacks neurons. Today, seventeen types of this disorder are known to medicine. Eleven of them were discovered in his laboratory.

Dalmau deflects credit with the ease of someone accustomed to the question. Nothing would have been possible, he insists, without the enormous effort of his team. There was no single eureka moment, no sudden clarity. The breakthroughs came from persistence, from spending countless hours with patients, watching their symptoms unfold and searching for patterns others had missed.

The story began with a 26-year-old American woman admitted to the University of Pennsylvania Hospital in a state of crisis. She lay in the intensive care unit on mechanical ventilation, her condition deteriorating despite every available test and intervention. Her medical history revealed something striking: she had arrived with what appeared to be a psychiatric episode—paranoid ideation, inappropriate behavior, aggression. Then neurological symptoms emerged. And she had a small benign ovarian tumor, a teratoma. Something clicked in Dalmau's mind. He recalled three other patients who had consulted with him, women with strikingly similar presentations. Drawing on his experience with cancer patients who developed immune-mediated nervous system complications, he proposed a hypothesis: these women might be suffering from immune-mediated inflammation of the nervous system.

The analysis confirmed it. All four patients carried antibodies against the NMDA receptor, a neurotransmitter receptor crucial for neural communication. They had discovered a new disease: anti-NMDA autoimmune encephalitis. It is a rare and terrible disorder, affecting primarily young people and children—the average age of onset is twenty-one—and striking women more often than men. Because the immune system attacks neurons, the first symptoms resemble psychosis: agitation, speech changes, erratic behavior. The disease can hide itself beneath a psychiatric diagnosis if no one thinks to look for autoimmune encephalitis.

Susannah Cahalan, a journalist at the New York Post, lived this deception firsthand. In 2009, at twenty-four, just two years after the disease's discovery, she developed anti-NMDA encephalitis. Her strange behaviors, insomnia, and paranoid convictions—that her home was infested with insects—were initially attributed to psychiatric illness. But she only worsened. She slurred her words, drooled, lost control of her swallowing. Her arms locked into unnatural positions. She moved slowly, barely able to walk without help. She believed she could age people with her mind. After a harrowing month, doctors at NYU Langone Hospital found the cause. Cahalan later wrote a book, "Brain on Fire," recounting her experience and reflecting on how many others with this disease had languished in psychiatric units for years, never knowing their condition was neurological, not psychiatric. Dalmau met with her when she was writing the book. He offered to contribute scientific explanations, but the editors removed them. He notes that everything in her account is accurate except one detail: she credits the chief of service with the diagnosis, but it was actually a young doctor trained in his lab at Penn who recognized the disease and sent the cerebrospinal fluid samples that confirmed it. He prefers not to discuss the 2016 Netflix film adaptation. He couldn't finish watching it.

Every week now, Dalmau receives emails from patients around the world thanking him for discovering disorders that would otherwise have remained hidden. Among them was Jeyden Liuzza, a Canadian girl diagnosed with anti-NMDA autoimmune encephalitis at three years old. Days after her third birthday, she began walking strangely, her foot turning inward. Within two days she was hospitalized, aggressive, biting her parents, striking doctors, experiencing abnormal movements and seizures. Her parents sent Dalmau at least twenty videos documenting her illness and recovery. In 2023, at eighteen, she presented him with the American Brain Foundation's award for his career. "It was very moving," he says.

Dalmau describes himself as a clinical neurologist with a bit of laboratory luck. Patients remain his compass. The research—animal models, sophisticated studies of how antibodies affect synapses—has always followed clinical observation. He is certain that without his work as a clinician, none of these discoveries would have happened. Others might have made them eventually, but not him. He has no plans to stop. Too much remains unknown. Why does the immune system attack what it should protect? In some cases, a tumor expresses proteins that also exist in the brain, triggering an immune response that mistakenly targets neural tissue. In others, genetic predisposition plays a role. Some cases begin with viral infection, herpes among them. "These are mechanisms we understand, but there is still much we do not," he says, his enthusiasm undiminished. He has always loved challenges. That is why, after earning his medical degree from the Autonomous University of Barcelona, he chose neurology and sought training in the United States. The brain has always fascinated him—not just its diseases, but how a healthy brain works. It remains a captivating puzzle: how this perfect data processor allows us to think, to know ourselves, to remember, to recreate moments and almost see our memories. He tells young researchers: if you want limitless investigation, what better than to study the organ that makes us who we are?