The court tasked New Zealand geriatrician John Campbell with assessing whether Ieng Thirith, 79, and three other former senior leaders, all charged with genocide and an array of other crimes, are physically fit to stand trial. It is sitting this week to debate his findings.

Defence lawyer Diana Ellis said Campbell’s report stated Ieng Thirith was cognitively impaired and asked the geriatrician about his conclusion that she was “very likely” suffering from Alzheimer’s.

“I think there are a number of factors that may be contributing [to Ieng Thirith’s mental state], and I think Alzheimer’s is certainly one of those,” Campbell replied.

Alzheimer’s is a progressively degenerative brain disease commonly associated with ageing. It can lead to memory loss, confusion and mood swings.

Ieng Thirith’s mental health has been a matter of speculation since her court outburst in early 2009 when she cursed those accusing her of crimes “to the seventh circle of hell.” Last week, the tribunal said it would appoint psychiatrists to determine whether Ieng Thirith was mentally fit to stand trial.

Such examinations would delay the start of the trial until 2012 because the tribunal wants to try the four defendants together.

Campbell said tests done on Ieng Thirith showed she could not complete a simple logic test and was unable to draw the hands on a paper clock to indicate the time.

Defendant Nuon Chea, 85, the Khmer Rouge’s chief ideologue, told the court Monday that his health was deteriorating but said he was keen to take part in his trial.

“But the most important thing is that I have problems concentrating,” Nuon Chea said, adding that he would be able to remain seated during trial “for about one and a half hours only.”  Asked later, Campbell said Nuon Chea’s assessment of being able to take part for such a short period each day “seems very reasonable.”

The other two defendants are former head of state Khieu Samphan and former foreign minister Ieng Sary. Neither is contesting his fitness to stand trial.

The tribunal has charged the four surviving leaders of the ultra-Maoist movement with genocide, war crimes and crimes against humanity in the second case to appear before it. All four denied the charges. They are aged 79 to 85 and suffer from various health problems.

In its first case, the court last year sentenced the regime’s security chief, Comrade Duch, to 30 years in prison after finding him guilty of war crimes and crimes against humanity. Duch has appealed his conviction.

The tribunal estimated 1.7 million to 2.2 million people died during the 1975-79 rule of the Khmer Rouge, which emptied Cambodia’s cities as it advocated a rural, agrarian society. It said 800,000 of those deaths were violent with the rest attributed to overwork, starvation and illness.