Willis was recently "diagnosed with aphasia, which is affecting his cognitive ability," according to his family.
Following a recent aphasia diagnosis, Bruce Willis decided to abandon his more than four-decade acting career, bringing attention to the relatively uncommon illness.
Aphasia is a neurological disorder in which a person's capacity to communicate verbally or in writing is impaired. 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, wrote on Instagram on Wednesday that her father's health has damaged his "cognitive capacities."
"As a result of this, and after much thought, Bruce has decided to leave the career that has meant so much to him," the message added.
Demi Moore, Rumer Willis' mother, also released a statement.
The most common cause of aphasia is stroke-related brain injury. A head injury, a brain tumour, an infection, or a degenerative condition like Alzheimer's can all cause it.
Willis' family declined to comment on the cause of his aphasia.
Willis, an Emmy Award winner and star of blockbusters including "Die Hard" and "The Sixth Sense," celebrated his 67th birthday this month.
What is the cause of aphasia?
According to the National Institutes of Health, aphasia is caused by impairment to one or more language-processing regions of the brain.
According to Dr. Adam Boxer, a professor of neurology at the University of California, San Francisco, aphasia commonly happens after a head injury or stroke, which shuts off blood flow 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.
"Aphasia affects a lot of people in a very subtle and insidious way," Boxer added.
What are the signs and symptoms of aphasia?
The intensity of aphasia's 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 only affect one element of language use. For example, a person with mild aphasia may fail to remember the names of items or to read or put words together into clear phrases.
Mild aphasia can be difficult to diagnose because most people experience mild memory loss as they age, according to Boxer: "Is it just ageing, or is it something else?"
Is aphasia a treatable condition?
Some types of aphasia, according to Boxer, can be treated and reversed if the reason is identified early.
According to Boxer, a stroke patient with aphasia may regain the ability to talk. However, the National Aphasia Association warns that if symptoms persist two or three months after a stroke, total recovery is improbable.
Despite this, the organization stated that "some people continue to improve over years, if not decades."
Slower aphasias, on the other hand, are usually diagnosed with a brain scan to rule out a tumor encroaching on the speech region of the brain or another neurological cause, according to Boxer.
A neurologist, according to Boxer, will focus on "what we can correct," such as a vitamin B-12 deficiency or a thyroid imbalance that could be contributing to the problem.
The patient works with a speech therapist to regain as much speech as possible once the cause has been discovered and addressed.
Loss of speech is caused by the "deterioration of brain tissue" caused by Alzheimer's or dementia in people who have primary progressive aphasia, or PPA, and "other problems associated with the underlying disease, such as memory loss, often occur later," according to the National Aphasia Association.
