Natasha McKenna (Courtesy of Natasha McKenna's family)

Natasha McKenna weighed only 130 pounds, but six deputies struggled to restrain her at the Fairfax County jail in February. They handcuffed, shackled, hit and wrestled the mentally ill woman, all with great effort, they said, for more than 20 minutes, before shocking her into submission with a Taser.

Minutes later, she stopped breathing. Days later, she died.

But when the Virginia medical examiner’s office issued the cause of her death last week, it declared that the Taser and use of force were not the primary factors. Instead, it was a rare and controversial syndrome that has been cited in dozens of deaths across the country after struggles with law enforcement: excited delirium.

Police, medical examiners and some doctors say the condition is real and frightening. Influenced by mental illness or the use of such stimulants as cocaine and methamphetamine, those in its grip often have extraordinary strength, are impervious to pain and act wildly or violently. Then, suddenly, some die.

Other medical experts and civil libertarians have questioned the existence of excited delirium and its frequent citation in cases that involve violent encounters between police and members of the public. Some say it is a cover for the use of excessive force by law enforcement.

A restraint chair in the Fairfax County jail, similar to one used to hold Natasha McKenna after deputies shocked her four times with a Taser on Feb. 3. She later died, and police are investigating. (Tom Jackman/The Washington Post)

Although no one is tracking how often excited delirium is cited in those police cases, Amnesty International found that the syndrome was cited in 75 of the 330 deaths following police use of a Taser on suspects between 2001 and 2008, according to Justin Mazzola, a researcher for the organization. The Washington Post found more than two dozen other examples in which excited delirium was cited in in-custody deaths. Those included deaths of people who had been restrained or had wrestled with officers, in addition to the Taser-related deaths.

Attorney Harvey J. Volzer said that McKenna’s family disputes the ruling in her case and that the deputies “tortured and killed” a woman suffering from schizophrenia and bipolar disorder. He urged officials to release a videotape that captured the incident.

The case places McKenna at the center of a hotly contested medical debate.

“They’ve come up with the concept that the individual is so excited they bring on their own death," said Douglas Zipes, a professor of medicine at Indiana University. “That you can be excited is without question. That you can be delirious is without question. But the concept of this being a syndrome causing death is incorrect and false.”

Vincent Di Maio, a retired forensic pathologist who has written a book on excited delirium, said that McKenna sounded like a prime candidate for the syndrome, given her history of mental illness and her struggle with officers. The condition has been “well documented,” he said, adding that critics are misguided in arguing that it does not exist.

“The original idea was noted in 1849 — if you go to medical literature, it shows up again and again over the years,” Di Maio said. “There’s no major scientific objection to it.”

McKenna, 37, was being held at the Fairfax jail on a charge of assaulting a police officer stemming from an incident in Alexandria in January. Alexandria police failed to pick McKenna up three times after she arrived at the jail on Jan. 26, so on the morning of Feb. 3, deputies with the Fairfax County Sheriff’s Office decided to transfer her themselves because her mental state was deteriorating.

McKenna had two previous violent encounters with deputies while at the jail, so the sheriff’s office sent a special team to remove her from her cell, according to incident reports.

McKenna became agitated after she was handcuffed through a food slot and tethered to a cell door. She began to pull out of the cuffs and began screaming, “You promised you wouldn’t hurt me!”

The deputies wrestled McKenna and eventually got her in shackles and put a hood over her head to keep her from spitting, according to incident reports. But they couldn’t fully seat her in a restraining chair.

She was shocked with a Taser in the thigh four times and was eventually strapped in the chair. A nurse checked McKenna’s pulse when they got to an entryway for the jail but found none.

Documents show that sheriff’s deputies began performing CPR on McKenna and that paramedics were called. McKenna’s heart stopped beating for 20 minutes, but she was resuscitated, according to incident reports. She was transferred to Inova Fairfax Hospital, where she later died.

A Virginia medical examiner ruled McKenna’s death an accident. The cause of death was listed as “excited delirium” associated with the use of physical restraint and the Taser, while schizophrenia and bipolar disorder were listed as contributing factors. No drugs were found in her system. The examiner did not respond to requests for comment.

Medical examiners in Miami were the first to use the term in the mid-1980s amid the cocaine epidemic sweeping South Florida. They noticed a spate of cases in which people had died after ingesting cocaine and acting deliriously. The use of the term then spread across the country.

Di Maio estimated there were 600 to 800 cases a year nationwide.

Deborah C. Mash, a professor of neurology at the University of Miami, said schizophrenics, bipolar patients and users of cocaine and methamphetamine are particularly prone to excited delirium. Their heart rates soar, and they become paranoid and delusional. Body temperatures can reach 105 degrees or higher.

The physiological mechanism of the syndrome is complex and remains poorly understood, but Mash said it probably involves an excess of neurotransmitters in the brain used to regulate organ functions.

“The signals between the heart and brain become chaotic. Normally, you have a feedback mechanism that will help to normalize respiration and cardiac rate and rhythm, but these fail,” Mash said. “The brain can be cooked.”

In one case, a Vancouver man lifted five police officers off him. A Dallas man, on a neighbor’s porch, stripped down to his underwear, screamed gibberish and waved a knife. In a third possible case, a man was found walking down a Detroit-area highway naked during a snowstorm.

Mash said the syndrome leaves no definitive anatomic signatures, so a medical examiner’s finding of excited delirium is one of exclusion, when all other possibilities are ruled out. The main evidence is the behavior before death.

Critics say the lack of clarity leaves excited delirium prone to abuse. Eric Balaban, senior counsel with the American Civil Liberties Union’s National Prison Project, called the syndrome an easy way to “whitewash” excessive use of force.

“It’s almost exclusively used in police-force cases,” Balaban said. “There seems to be a high correlation between its use by medical examiners and in-custody deaths.”

Rulings of excited delirium have helped clear officers of wrongdoing in use-of-force death cases and clear the Taser’s manufacturer in lawsuits over deaths after the use of the stun devices.

Steve Tuttle, a spokesman for Taser, said the science behind excited delirium is solid. “You’ve got an enormous amount of research,” Tuttle said.

There is no consensus on excited delirium among major medical groups. The American College of Emergency Physicians and the National Association of Medical Examiners recognize the condition, but others — including the American Medical Association and American Psychological Association — have not taken a stand.

“We are . . . aware of an ongoing debate within the professional literature about such a diagnosis,” the APA said in a statement. “Ultimately, more research on the concept of ‘excited delirium’ needs to be undertaken.”