TAIPEI, Taiwan — Taiwan's former President Chen Shui-bian was granted a one-month medical parole Monday for treatment of neural degeneration, more than four years into his 20-year prison sentence for corruption.

Chen, 64, rolled down a car window and waved to about 200 supporters while a police escort took him out of the main gate at Taichung prison on Monday afternoon.

Chen, whose election in 2000 ended a 50-year monopoly on power by the island's Nationalists, or Kuomintang, and who moved to expand Taiwan's de facto independence from mainland China, went on trial shortly after the end of his 2000-2008 tenure.

He was convicted in September 2009 of more than $12 million in embezzlement and bribe-taking in what he denounced as a persecution driven by his political opponents.

Chen has reportedly suffered from depression, sleep apnea, heart ailments and neural degeneration while behind bars, and authorities say he has attempted suicide.

The one-month medical parole was granted for treatment of his neurodegeneration, which was worsening despite efforts to treat him while in prison, the Justice Ministry said in a statement.

"It is believed that only on medical parole can his life and health be ensured," the ministry said.

Neurodegeneration is an umbrella term for the loss of function of the neurons as experienced in diseases such as Parkinson's, Alzheimer's and Huntington's. The ministry did not specify what kind of neurodegeneration Chen was suffering from.