Bruce Willis’ decision to halt his more than four-decade-long acting career following a recent aphasia diagnosis has shone a light on the relatively uncommon illness.

Aphasia is a neurological disorder that impairs a person’s capacity to communicate vocally or in writing. According to the National Aphasia Association, it affects an estimated 2 million people in the United States, with about 180,000 new cases diagnosed each year.

Rumer Willis, Willis’ daughter, stated on Instagram on Wednesday that her father’s “cognitive faculties” had been impacted by the ailment.

“As a result of this, and with considerable thought,” the post added, “Bruce is moving away from the career that has meant so much to him.”

Demi Moore, Rumer Willis’ mother, also issued a statement.

Stroke-related brain injury is the most prevalent cause of aphasia. It can also be caused by a head injury, a brain tumour, an infection, or a degenerative disease such as Alzheimer’s.

Willis’ family did not provide any information about the cause of his aphasia.

Willis, an Emmy-winning actor who starred in blockbusters such as “Die Hard” and “The Sixth Sense,” turned 67 this month.

What causes aphasia?

According to the National Institutes of Health, aphasia is caused by injury to one or more parts of the brain that interact with language.

According to Dr. Adam Boxer, a professor of neurology at the University of California, San Francisco, aphasia frequently happens after a head injury or a stroke, which shuts off blood supply to parts of the brain important for speaking.

Aphasia can also develop gradually as a result of the progression of a brain tumour, a neurological condition, or an infection, according to Boxer.

“A lot of people have sort of a very slow and insidious onset of aphasia,” Boxer said.

What are aphasia’s symptoms?

The intensity of aphasia symptoms varies. According to the National Aphasia Association, the illness can “make contact with the patient practically difficult” in the most severe situations.

When aphasia is moderate, it may damage only one element of language usage. A person with moderate aphasia may fail to remember the names of items, or may struggle to read or put words together into clear phrases.

Because most individuals have modest memory loss as they age, mild aphasia can be difficult to distinguish, according to Boxer: “Is it just ageing, or is it something else?”

Is aphasia treatable?

Some kinds of aphasia, according to Boxer, can be treated and reversed if the underlying reason is identified early.

According to Boxer, a stroke patient with aphasia may regain the capacity to talk. However, if symptoms persist two or three months after a stroke, total recovery is improbable, according to the National Aphasia Association.

Nonetheless, the group stated that “some people continue to progress over years and even decades.”