Otto Warmbier, a university student, returned home to the United States in a coma this week after being detained in a North Korean prison for 17 months.
He had been sentenced to 15 years of hard labour for stealing a propaganda item during a trip to the country with a group of young tourists.
Upon returning him to the United States, North Korean officials said they had released him on humanitarian grounds after he contracted botulism from a sleeping pill.
However, doctors at the University of Cincinnati argue the student and prisoner has no sign of botulism in his system.
The university's Dr Daniel Kanter says Otto Warmbier is suffering from spastic quadriparasis.
"His neurological condition can be best described as a state of unresponsive wakefulness. He has spontaneous eye opening and blinking. However, he shows no signs of understanding language, responding to verbal commands or awareness of his surroundings. He has not spoken. He has not engaged in any purposeful movements or behaviours."
While doctors are uncertain about what exactly caused the condition, cardiac arrest that stops the blood flow to the brain is generally seen as a result of the death of brain tissue.
Doctors have also confirmed Otto Warmbier has no broken bones.
His father, Fred Warmbier, says the family has been what he termed "brutalised with misinformation" since their son was imprisoned.
He says there is no excuse for North Korea keeping his son's condition secret.
And he says he is frustrated by how long it took to bring him home but relieved to have him back on US soil.
Mr Warmbier is warning other US students about travelling overseas and says North Korea draws in Americans to take them hostage.
"The North Koreans lure Americans to travel to North Korea via tour groups run out of China, who advertise slick ads on the Internet proclaiming, 'No American ever gets detained off our tours' and 'This is a safe place to go.' And then they take them hostage, and then they do things to them, and that's what happened to my son."
US State Department spokeswoman Heather Nauert has confirmed the department's special envoy on North Korea, Joseph Yun, has met with three other current US detainees.
"I can confirm that Ambassador Yun did make contact with the three Americans who are being held there. We are happy that he was able to make that contact. In terms of their medical condition, that's something I cannot comment on. The other day, I said I won't comment on personal health matters."
Tensions between the United States and North Korea have been heightened by North Korean missile launches and two nuclear-weapons tests.
The Warmbier family says it spoke with US president Donald Trump the day after Otto Warmbier returned home.
