"Look at my face, listen to my [poor] articulation. These are just small indications of the problem I had. What happened to me is not a problem of food or my eating habits. It is a problem of the political regime in this country," Yushchenko said.
Yushchenko's health worries began on 5 September, when the former prime minister began to fall sick. Five days later, he was transported to a private clinic in Vienna, Rudolfinerhaus. By this time he was gravely ill, with a whole range of baffling symptoms.
Nikolai Korpan was Yushchenko's chief physician in Vienna. He describes the symptoms in a telephone interview with RFE/RL.
"He had acute pancreatitis [inflammation of the pancreas], he had acute gastritis, he had acute proctocolitis, acute myositis [eds: muscle inflammation], acute paralysis of the facial nerve and he was [describing] different pain symptoms, for example in the area of the abdominal cavity and the thorax cavity, the breast cavity," Korpan says.
Korpan told RFE/RL the combination of symptoms made Yushchenko's case particularly challenging to diagnose.
"This case is not a typical case in medicine. It's an atypical case. It is seldom that one observes in clinical practice complex acute diseases combined with neurological signs," Korpan says.
Korpan says a total of 20 specialists, ranging from neurologists to dermatologists, worked on Yushchenko's case. Under their care, Yushchenko's health rapidly improved. But the doctors were never able to establish a precise diagnosis.
Korpan says his patient could have suffered from an unidentified viral infection or something more sinister -- like intentional poisoning. He excludes the possibility of accidental food poisoning.
"We can say that maybe [the illness] could [have been caused by a] special atypical agent, but not simple food or drink," Korpan says.
Korpan says blood tests were unable to determine the nature of the atypical agent or virus.
"We sent blood for different special analyses and we received the answer that after 96 hours after the beginning of the [illness], it's not possible to confirm the special agent in the blood," Korpan says.
Yushchenko, upon his release from the clinic, said the doctors' statements proved he had been intentionally poisoned. In fact, the Viennese doctors left this open as a possibility, but reached no definitive conclusions.
For another view, RFE/RL spoke by telephone with Dr. Marc Siegel in New York. Siegel, an associate professor at New York University's School of Medicine, is a specialist in internal medicine and has written for "The New York Times", "The Washington Post," and other U.S. publications on health issues.
First, Siegel says Yushchenko's symptoms, as described by Dr. Korpan, do not sound like ricin poisoning, which usually involves significant respiratory problems.
Siegel also disputes the idea that food poisoning could be ruled out in Yushchenko's case -- especially if no final diagnosis was ever established.
"I'm going to say two things: one, I don't see how, without knowing exactly what this is, they can say for certain that he wasn't poisoned [by his food]. And two, I think that there are certain bacteria that you can get by eating bad food that can give you multi-system involvement," Siegel says.
Siegel says there are many bacteria, for example, "e-coli" and salmonella, that frequently cause food poisoning. He says these can produce a wide array of dramatic symptoms and affect many organs at once.
"These bacteria make toxins -- campylobacter especially -- that can affect many organs beyond just the [gastrointestinal tract], so I'm not hearing anything to make me convinced this isn't food poisoning," Siegel says.
Siegel says the fact that made a relatively quick recovery, indicates his illness may have been virus.
"When he [got] better, it could be because a virus tends to get better untreated. There is no cure for a virus. Some respond to anti-viral therapy, like influenza does. But most viruses just run their course, so the fact that he got better does speak to the possibility of a full-blown viral illness," Siegel says.
Siegel finds it hard to understand why the blood tests were so inconclusive. He takes issue with the contention that it was just too late for the blood tests to reveal anything.
"Well, I don't think that is so! In terms of testing for viruses, it's a perfect time to test. You're talking about serology. What you do is you test for the presence of antigens and antibodies in the blood, antibodies to a particular virus. Ninety-six hours [after the onset of illness] is exactly when you would expect to find it. So I don't think that 96 hours out would be a time when you could exclude a virus, I think it's when you would exactly diagnose a virus. And, as far as toxins that might have been introduced into the system, I certainly don't think that they would have cleared the system in 96 hours either. Most toxins are not metabolized that quickly. So it's puzzling to me that in terms of forensics, they couldn't try to track this down," Siegel says.
There is, however, one other possible explanation, although it sounds too simple to be true: the flu. Siegel says there are some viruses whose presence is sometimes impossible to confirm through blood analysis. Among the leading culprits are influenza strains.