Last year, after police had placed Elijah McClain in a chokehold, then handcuffed him, paramedics injected him with a dose of ketamine, a powerful sedative. They said he "appeared to be" exhibiting signs of "excited delirium"; he subsequently went into cardiac arrest and died. Earlier this year, police officers in Tacoma, Wash., cited excited delirium in the case of another unarmed black man, Manuel Ellis, who died in custody. And as Derek Chauvin knelt on George Floyd's neck for the final moments of his life, a fellow police officer said, "I am concerned about excited delirium or whatever." This may be part of Chauvin's defense against murder charges.

Across the United States, police officers are routinely taught that excited delirium is a condition characterized by the abrupt onset of aggression and distress, typically accompanying drug abuse, often resulting in sudden death. One 2014 article from the FBI's Law Enforcement Bulletin describes "excited delirium syndrome" as "a serious and potentially deadly medical condition involving psychotic behavior, elevated temperature, and an extreme fight-or-flight response by the nervous system."

How often is excited delirium invoked? It's unclear, but in Florida at least 53 deaths in police custody were attributed to it over the past 10 years. One study showed that 11% of sudden unexplained deaths in police custody in Maryland from 1990 to 2004 were attributed to excited delirium.

The American College of Emergency Physicians published a controversial position paper in 2009 stating its consensus that excited delirium is a valid disease, associated with a significant risk of sudden death.

But excited delirium is pseudoscience. It's not a concept recognized by the American Medical Association or the American Psychiatric Association. It isn't a valid diagnosis; it's a misappropriation of medical terminology, and it doesn't justify police violence.

While delirium is a well-recognized diagnosis frequently seen and treated by neurologists and psychiatrists, excited delirium is not. Delirium is defined in the Diagnostic and Statistical Manual of Mental Disorders as an acute, fluctuating disturbance in attention and cognition, typically provoked by an underlying medical condition such as infection, drug intoxication, a medication's adverse effects or organ failure. It can have "hyperactive" or "hypoactive" features, meaning that patients may be agitated or drowsy, or may move between these states.

Delirium is not associated with sudden unexpected death.

Excited delirium, on the other hand, stems from an 1849 description by Luther V. Bell in the American Journal of Insanity. Bell looked at 40 patients admitted with "fever and delirium" to the psychiatric facility at McLean Hospital in Boston. Proponents of the excited delirium diagnosis refer back to Bell's description as historical data, but the cases he studied did not involve deaths occurring in the span of minutes to hours, but rather two or three weeks after admission. While it is not possible to retrospectively diagnose these patients, it's likely that many of them suffered from forms of infectious or autoimmune encephalitis.

Despite these shaky origins and the lack of grounding in medical science, this concept − of a febrile, agitated state often culminating in death − has persisted, advanced by law enforcement. The features of this purported condition, as listed by the American College of Emergency Physicians, betray its entanglement with law enforcement, including "bizarre behavior generating phone calls to police," "failure to respond to police presence" and "continued struggle despite restraint." Several analyses have found that most deaths attributed to "excited delirium" are associated with the use of physical restraint. Some emergency-medicine doctors who are proponents of the diagnosis have been criticized for having conflicts of interest with the stun gun industry. And the manufacturer of Tasers has helped popularize this diagnosis to help attribute Taser-associated deaths to other possible causes.

The syndrome is disproportionately diagnosed among young black men, highlighting the racist undertones of the reported clinical symptoms: having "superhuman strength" and being "impervious to pain." It winds up being a convenient scapegoat cause of death after a violent confrontation.

Excited delirium implies that there is a medical condition that predisposes certain individuals, often black men, to die in police custody. It draws upon aspects of real medical conditions such as delirium, psychosis, drug intoxication and sudden cardiac death. But it manipulates them to form a broadly applicable blanket diagnosis that serves the interests of law enforcement and absolves officers of accountability.

Méabh O'Hare is a neuromuscular fellow at Massachusetts General Hospital and Brigham and Women's Hospital. Joshua Budhu is a neuro-oncology fellow at Massachusetts General Hospital, the Dana Farber Cancer Institute and Brigham and Women's Hospital. Altaf Saadi is a general academic neurologist at Massachusetts General Hospital and an instructor of neurology at Harvard Medical School. They wrote this for The Washington Post.