London, England (CNN) -- A Belgian car crash victim who was misdiagnosed as being in a vegetative state for 23 years was conscious the whole time, it has emerged.
For years he listened to the conversations going on around him but he was unable to communicate with his doctors or family.
Rom Houben was 23 at the time of the near-fatal car crash in 1983 that left him paralyzed. Doctors presumed he was in a vegetative state following the accident and they believed he could feel and hear nothing.
Neurologist Dr.Steven Laureys of the University of Liege, in Belgium carried out a brain scan using state-of-the art scanning system and discovered that Houben's brain was fully functional.
In an interview with the UK's ITV news Monday, Rom communicated by typing on a special keyboard attached to his wheelchair, and aided by his carer.
He said: "At some moments it was terribly lonely but I knew my family was believing in me."
"I simply want to enjoy life," he added. "I notice a big difference now I'm back in contact with the world."
The case has highlighted the difficulties doctors face when trying to diagnose the level of consciousness of a patient in a coma-like state.
A study carried out last year on 103 patients by Laureys and his colleagues at Liege's Coma Science Group found that 41 percent of patients in a Minimally Conscious State (MCS) were misdiagnosed as being in the much more serious Vegetative State (VS).
Dr. Daniel Hanley, professor of neurology at Johns Hopkins Medicine, in Maryland, told CNN that VS is a coma-like state in which patients have a sleep and wake cycle, and can show reflex chewing, swallowing and blinking, but don't respond to language or stimulation.
Patients in MCS occasionally show they are aware of their environment, for example moving to face a doctor when asked, but only infrequently.
Laureys said of his research, "Differentiating the vegetative from the minimally conscious state is often one of the most challenging tasks facing clinicians involved in the care of patients with disorders of consciousness.
"Misdiagnosis can lead to grave consequences, especially in end-of-life decision-making."
Caroline Schnakers, who carried out the research with Laureys, told CNN that one probable reason for the high rate of misdiagnosis is that doctors often base their diagnosis on observations of a patient's behavior, rather than assessing patients using standardized tests.
"Assessment is usually behavioral," Schnakers told CNN. "For example, if you come into a room and a patient's eyes follow you, or if they smile when you make a joke, they are conscious -- but it doesn't mean they will still be able to do that one hour later."
Schnakers said that using standardized tests could reduce incidents of misdiagnosis.
The Glasgow Coma Scale is a standardized test that classifies a patient's motor, verbal and eye response on a graded scale. It was widely used until about 2000 to classify a patient's level of consciousness, but Schnakers says it may contribute to misdiagnosis.
She told CNN, "In our study we used the JFK Coma Recovery Scale-Revised (CRS-R), which is standardized for detecting signs of consciousness in someone recovering from a coma. It's very sensitive and avoided a lot more misdiagnosis than the Glasgow Coma Scale."
The CRS-R was developed at the JFK Johnson Rehabilitation Institute and grades patients' verbalization, communication, motor function, visual function and response to sound.
Diagnosis can be further complicated by another condition, called Locked-In Syndrome. Much less common than VS or MCS, patients in a locked-in state are totally aware of their environment but have minimal reflexive movements, typically only being able to blink their eyes. Hanley told CNN that Houben may have been in a locked-in state.
But Houben's diagnosis may have been made more difficult by the fact that he was partly paralyzed, meaning he was unable to show a motor response.
"He was conscious for a long time, but it's difficult to know for how long," said Schnakers. "Maybe he had a period of VS, but you wouldn't know how long it lasted, even if you ask a patient how long they were in VS or MCS."
Hanley explained that diagnosis is also more difficult if a patient is being treated with sedative drugs, which can cause severe neurological impairment that can mimic VS. But even given those considerations, Hanley says neurologists should easily be able to tell the difference between a patient in VS and MCS.
Dr. Nicholas Schiff, of the Weill Cornell Medical Center, in New York, told CNN that the risk of misdiagnosis is increased because a patient's condition can change over a long period and the transition from VS to MS often takes place outside the time window of careful assessment.
"The 'standard' is probably transfer to nursing home from acute care at an early stage, where an accurate diagnosis of VS gets replaced at the nursing home with an inaccurate prognosis of permanent VS, explicitly or implicitly," Schiff said.
"Because there are no standards for reassessment or any access to rehabilitation centers for many of these patients this is the status quo."
CNN's Caleb Hellerman contributed to this story.