Chen Shui-bian has been hospitalized since Sept. 21 for various health issues, including severe depression, benign enlargement of the prostate and urinary tract and prostate infections, The Central News Agency reported Thursday.
Chen's right hand was recently observed trembling, the hospital said.
A series of tests have ruled out a stroke or Parkinson's as the cause.
Chen is serving an 18 1/2-year prison sentence for corruption.
Notable deaths of 2014 [PHOTOS]