The Senate has been advised that Liberal Senator Joyce Fairbairn will not be returning to Parliament Hill this fall because she is suffering from dementia.

Conservative Senator David Tkachuk, who chairs the committee that deals with administrative matters in the Senate, said he was advised by a family member of Fairbairn's in writing in mid-August that she wouldn't be coming back to work. The letter was also sent to the clerk of the Senate.

"All we've received is a letter saying that she won't be coming back and that she is under care and that she suffers from the terrible disease of dementia, Alzheimer's," he told CBC.

Tkachuk said it is his understanding that Fairbairn, an Alberta senator, signed a power of attorney and that others have been in charge of her affairs since April. He said it is also his understanding that a psychiatrist declared her mentally incompetent in February and that he has asked for documentation of that.

He is also seeking a legal opinion on what steps, if any, the Senate needs to take.

Fairbairn, 72, was appointed to the Senate in 1984, and was a journalist who also worked in the office of former prime minister Pierre Trudeau for many years. Outside of her work on Parliament Hill, Fairbairn has been an advocate for literacy and the Paralympics. In 2003 she was chair of the Canadian Paralympic Foundation.

If a senator misses six consecutive days of work a medical certificate must be produced. After a certain period of time an extended medical leave can be requested.

Despite her health problems Senator Fairbairn hadn't yet missed six straight days of work, Tkachuk said. "She was there and voted until the end of June," he said.

Tkachuk said he didn't want to comment on whether he saw any signs of her illness while she was working or on whether there are any concerns about her voting on legislation.

"I feel very sorry for all of this and what's happened to her. I like Senator Fairbairn very much, I've worked with her on committees, she's been around a long time. I wish her well," he said.

Tkachuk's own father had Alzheimer's disease and he said he knows firsthand how difficult it is for the person who has it and their family.

"His memory was being erased," he said, noting how frustrating it was for his father. "To watch that as a son or a daughter is ... it's just not pleasant."

The Liberals wouldn't confirm that it is Alzheimer's that is keeping Fairbairn from coming back to work in September and would only say that health issues are forcing her to take sick leave.

"Any further status change will be depending upon her health condition," said Marc Roy, director of communications for Senator James Cowan, leader of the Liberals in the Senate.

"Her attendance and participation in the spring, and in the past, was very normal and I can't evaluate how a person's state of mind is and I won't comment on that," he said.

Fairbairn is close to the mandatory retirement age for senators, 75.