Aphasia describes a neurological condition that affects a person’s ability to communicate verbally or through writing. It affects an estimated 2 million people in the U.S., and nearly 180,000 acquire it every year, according to the National Aphasia Association.
Willis' daughter Rumer Willis posted Wednesday on Instagram that the condition has affected her father's "cognitive abilities."
"As a result of this and with much consideration Bruce is stepping away from the career that has meant so much to him," the post said.
Rumer Willis' mother, the actor Demi Moore, also shared the statement.
The most common cause of aphasia is brain damage from a stroke. It can also arise as a result of a head injury, a brain tumor, an infection or a degenerative disease like Alzheimer's.
Willis' family did not offer details about the cause of his aphasia.
Willis, an Emmy-winning actor and the star of hit movies like "Die Hard" and "The Sixth Sense," turned 67 this month.
What causes aphasia?
Aphasia is caused by damage to one or more areas of the brain that deal with language, according to the National Institutes of Health.
Aphasia often occurs after a head injury or a 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 can develop gradually with the growth of a brain tumor, a neurological disease or an infection.
"A lot of people have sort of a very slow and insidious onset of aphasia," Boxer said.
What are aphasia’s symptoms?
Aphasia’s symptoms vary, as can their severity. In the most serious cases, the condition can “make communication with the patient almost impossible,” according to the National Aphasia Association.
When it is mild, aphasia may affect just a single aspect of language use. A person with mild aphasia might not be able to recall the names of objects, for example, or might struggle to read or put words together into clear sentences.
Because most people experience mild memory loss as they age, Boxer said, mild aphasia can be hard to discern: “Is it just aging, or it is something else?”
Is aphasia treatable?
Boxer said some forms of aphasia can be treated and reversed if the cause is caught early.
A stroke patient suffering from aphasia might regain the ability to speak, Boxer said. But the National Aphasia Association said complete recovery is unlikely if symptoms remain two or three months after a stroke.
Still, the organization noted that "some people continue to improve over a period of years and even decades."
But with slower aphasias, Boxer said, doctors will typically start with a brain scan to rule out a tumor pressing on the speech section of the brain or some other neurological cause.
Boxer said a neurologist will focus on "what we can fix," such as a vitamin B-12 deficiency or a thyroid imbalance that might be contributing to the condition.
Once the cause is identified and treated, the patient works with a speech therapist to regain as much speech as possible.
If the person has primary progressive aphasia, or PPA, loss of speech is due to the "deterioration of brain tissue" caused by Alzheimer's or dementia, and in that case, "other problems associated with the underlying disease, such as memory loss, often occur later," the National Aphasia Association said.