The Willis family said he was recently "diagnosed with an aphasia, which has an impact on his cognitive abilities."
Bruce Willis's decision to end his acting career spanning more than four decades after being recently diagnosed with aphasia has shed light on a somewhat rare disorder.
Aphasia describes a neurological condition that affects a person's ability to communicate either verbally or in writing. According to the National Aphasia Association, it It affects an estimated 2 million people in the U.S., and about 180,000 get it each year.
Willis's daughter Rumer Willis posted on Instagram on Wednesday that the condition affected her father's "cognitive abilities."
"As a result and with much consideration, Bruce is walking away from a career that means a lot to him," Post said.
Rumer Willis' mother, actor Demi Moore, also shared the statement.
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The most common cause of aphasia is brain damage from a stroke. It can also arise as a result of a head injury, brain tumor, infection or a degenerative disease such as Alzheimer's.
Willis's family did not provide details about the cause of his aphasia.
Emmy-winning actor and star of hits like "Die Hard" and "The Sixth Sense" Willis turns 67 this month.
What causes aphasia?
According to the National Institutes of Health, aphasia is caused by damage to one or more areas of the brain related to language.
Aphasia often occurs after a head injury or stroke, which cuts off blood flow to areas of the brain responsible for speech, said Dr. Adam Boxer, a professor of neurology at the University of California, San Francisco.
Other times, Boxer said, aphasia may develop slowly with the development of a brain tumor, a neurological disease, or infection.
"Many people have a very slow and insidious onset of aphasia," Boxer said.
What are the symptoms of aphasia?
Symptoms of aphasia vary, as do their severity. In the most severe cases, the condition can "make communication with the patient nearly impossible," according to the National Aphasia Association.
When it is mild, aphasia may affect only one aspect of language use. For example, a person with mild aphasia cannot remember the names of objects, or may struggle to read or put together words in clear sentences.
Since most people experience mild memory loss with age, Boxer said, mild aphasia can be difficult to understand: "Is it just aging, or is it something else?"
Is aphasia treatable?
Boxer said some forms of aphasia can be treated and reversed if the cause is caught early.
Boxer said that a stroke patient suffering from aphasia may regain the ability to speak. But the National Aphasia Association says a complete recovery is unlikely if symptoms persist two or three months after a stroke.
Still, the organization notes that "some people continue to improve over a period of years and decades."
But with slow aphasia, Boxer said, doctors will usually start with a brain scan to rule out tumors pressing on the speech segment of the brain or any other neurological cause.
Boxer said a neurologist would focus on "what we can fix," such as vitamin B-12 deficiencies or thyroid imbalances that may contribute to the condition.
Once the cause is identified and treated, the patient works with a speech therapist to get as much speech back as possible.
If the person has primary progressive aphasia, or PPA, the loss of speech is due to "degeneration of brain tissue" due to Alzheimer's or dementia, and in that case, "other problems associated with the underlying disease, such as memory loss, often occurs later," the National Aphasia Association said.