But it’s unclear what exactly happened to Warmbier and what his medical condition was when he arrived in the United States late Tuesday. The plane carrying Warmbier landed in Cincinnati, where he was placed in an ambulance and taken to University of Cincinnati Medical Center.
Whether the student actually had botulism — a rare and serious disease not typically associated with loss of consciousness — remains unconfirmed. And how a sleeping aid could have triggered a coma is also questionable. What experts can say definitively is that the prognosis is grim for someone who has been comatose for such a lengthy period.
Botulism, which is most commonly contracted by ingesting contaminated food or through an infected wound, is caused by a highly potent toxin produced by the bacteria Clostridium botulinum. The disease typically progresses quickly and can cause double or blurred vision, slurred speech, trouble swallowing or breathing and, in severe cases, muscle paralysis and respiratory failure, according to the Centers for Disease Control and Prevention.
Pritish Tosh, an infectious diseases physician and researcher at the Mayo Clinic, said a coma is not a typical complication. Botulism patients “tend to be mentally quite alert despite the progressive paralysis,” he said, though patients who need to be put on a ventilator may be put into a medically induced coma “as part of their supportive care.”
James Bernat, a coma expert at the Dartmouth-Hitchcock Medical Center in New Hampshire, noted that in a typical poisoning case, patients who are in a coma generally begin to gain consciousness once the substance has been cleared from their body. But with botulism, the toxin binds where nerves and muscles meet. If the poisoning is severe enough, “it could lead to respiratory muscle paralysis, causing respiratory and cardiac arrest, which could deprive the brain of oxygen,” he said.
With adequate medical care, which can include mechanical ventilation and an antitoxin to halt progression of the infection, the survival rate is more than 90 percent, according to the experts, who stressed that they could not comment specifically about Warmbier's condition. Yet the outcome in any case depends on the care provided early on. That's another critical unknown with Warmbier.
Bernat said the prognosis for recovery from a coma or vegetative state depends on not just what caused it but how long it has lasted. After a year, a person's chance of full recovery would be dim.
“I would put it in the category of being extremely unlikely,” agreed Ariane Lewis, an assistant professor of neurology and neurosurgery at New York University’s Langone School of Medicine. “But I wouldn’t say it’s impossible. After protracted periods of time of being unarousable, that moves it further and further away from being possible.”
Technically, experts consider comas a temporary state. Beyond about 30 days, a person who remains completely unaware of themselves or their environment is said to be in a persistent vegetative state. One step up from that is a minimally conscious state, in which patients show some awareness of their environment, some response to pain and the ability to track an object with their eyes.
Comas are measured on the Glasgow Coma Scale, which scores on eye, motor and verbal responses from a total 3 (worst) to 15 (best).
Traumatic brain injury is the most common cause of comas in the United States, said Debra Babcock, director of the cognition program at the National Institute of Neurological Disorders and Stroke, part of the National Institutes of Health. But the condition can follow stroke, infection, kidney failure and overdoses, among other issues.
Babcock agreed that botulism infection is a highly unlikely cause since the toxin released by the bacteria generally does not cross the protective blood-brain barrier. But an overdose of a sleeping medication might lead to a coma, she said. Giving such medication to a person with breathing difficulty would not be standard practice in the United States, she added, because of fear that the sedative could depress respiration.
Once Warmbier is evaluated by U.S. doctors, his care could involve visual, auditory and motor stimulation in an effort to improve brain function, Babcock said. One clinical trial has shown that the drug amantadine may help in traumatic brain injury cases.
“It’s a horrible situation, and we just hope he’ll get the best possible care,” she said.
Susan Svrluga, reporting from Cincinnati, contributed to this report, which has been updated.