MANILA (Reuters) - Philippine President Rodrigo Duterte said he has a chronic neuromuscular disorder called myasthenia gravis that is causing one of his eyelids to droop.

FILE PHOTO: Philippine President Rodrigo Duterte speaks with an official during his meeting with Chinese President Xi Jinping at the Diaoyutai State Guesthouse in Beijing, China, August 29, 2019. How Hwee Young/Pool via REUTERS

Duterte made the comment about his condition while speaking on Saturday to the Filipino community in Russia, where he was on a working visit.

“It is a nerve malfunction,” Duterte said, explaining to the crowd why one eye appears smaller than the other. His remarks were contained in a transcript that was emailed to the media in the Philippines on Sunday.

There is no cure for myasthenia gravis, an illness that causes muscle weakness, but treatment can help relieve symptoms.

The firebrand leader, 74 is known for a busy schedule and for giving long speeches, often several a day. Several disappearances from public view in the past fueled rumors he is in declining health. The government has repeatedly denied that.

Duterte’s latest comments could raise more questions about the state of his health.

Duterte’s known ailments include back problems, migraines due to nerve damage after a motorcycle accident and Barrett’s oesophagus, which affects his throat. He also suffers from Buerger’s disease, caused by his heavy smoking in younger days, which can cause blockages in the blood vessels.

Last October, Duterte underwent a colonoscopy, a procedure to check the health of the rectum and lower bowel, which officials said the president does on yearly basis.

The Philippine Constitution mandates that the public must be informed of the state of the president’s health in case he has a serious illness.

Under Philippine laws, if a sitting president dies in office, is permanently disabled or removed through impeachment, the vice president takes over and serves the remaining years in a six-year, single term. Vice President Leni Robredo, a leader of the political opposition, was elected in 2016, the same year Duterte was elected.