Nearly a year after Bruce Willis’s family announced he would step away from acting after being diagnosed with aphasia, they say his condition has progressed in an alarming way.

In a statement, the 67-year-old actor’s family said Willis had a more specific diagnosis of frontotemporal dementia.

“While this is painful, it is a relief to finally have a clear diagnosis,” Thursday’s statement read.

“FTD is a cruel disease that many of us have never heard of and can strike anyone.”

Last March, Willis’s family said his aphasia had affected his cognitive abilities. The condition causes loss of the ability to understand or express speech.

In Thursday’s statement, his family said communication challenges were just one symptom of frontotemporal dementia.

“Today there are no treatments for the disease, a reality that we hope can change in the years ahead,” the statement read.

“As Bruce’s condition advances, we hope that any media attention can be focused on shining a light on this disease that needs far more awareness and research.”

The statement was posted on the website for The Association for Frontotemporal Degeneration and signed by Willis’s wife, Emma Heming Willis, his ex-wife Demi Moore, and his five children, Rumer, Scout, Tallulah, Mabel and Evelyn. Moore also posted it on her own Instagram.

Until this week’s announcement, the most recent news from Willis’s family had been a rare family photo surrounded by his beloved blended family.

In an Instagram photo, also shared by Moore, just before Christmas, Willis delivered one of his classic smiles as he stood with daughters Tallulah, Scout and Rumer.

Hemming and her two daughters with Willis were also in the festive shot.

“We are family. Getting into the holiday spirit,” Moore wrote.

A month later, 34-year-old Rumer Willis announced she was expecting her first child with partner Derek Richard Thomas. The baby will be a first grandchild for Moore and her former husband.

Over a four-decade career, Willis’ movies had earned more than $US5 billion ($7.2 billion) at the worldwide box office.

He achieved initial fame for the 1980s comedy-drama TV series Moonlighting before he became the tough guy, action hero who shouted “Yippee Ki Yay” in five Die Hard films, and winning acclaim for roles in Pulp Fiction and The Sixth Sense.

In recent years, the prolific actor had primarily featured in direct-to-video thrillers. He has won one Golden Globe Award and two Emmys.

-with AAP