What to know about aphasia, the language disorder that has prompted Bruce Willis to quit acting

• Bruce Willis is stepping away from acting after being diagnosed with aphasia, his family said. 
• Aphasia is a language-communication disorder that typically occurs after a stroke or brain injury.
• Willis may have have a neurodegenerative form. The condition is treated with speech-language therapy. 

Bruce Willis has aphasia, a language and communication disorder, his family announced on Instagram Wednesday. 

"As a result of this and with much consideration Bruce is stepping away from the career that has meant so much to him," Rumer Willis, his daughter with Demi Moore, said in the post.

Aphasia affects over 2 million Americans of all ages, and is typically a consequence of a stroke or other brain injury. It's unclear what, if anything, caused Willis's condition. 

He may have a form called primary progressive aphasia, a neurodegenerative disease in which language abilities and cognitive function decline, speech pathologist Brooke Lang told Insider. The 67-year-old action star has been reportedly suffering from early-onset memory loss for several years. 

Typically, though, aphasia doesn't reflect cognitive deficits. 

Aphasis can make comprehending and saying certain words difficult

People with aphasia may stutter or slur certain words, and struggle to find the right terms. Reading or hearing concepts like up and down, left and right, and the time of day can also take time for some people with the condition to interpret. Some people develop a propensity for curse words. They can be mistaken for drunk.

That was the case for one 26-year-old nurse, Bryn Bowles, who developed aphasia after suffering a sudden brain bleed. 

While visiting the Grand Canyon, she asked a staffer for directions to the restroom. Because the words "left" and "right" sound similar to her, she paused before going into the correct one. When leaving, she mistakenly tried the entrance-only door. 

The employee sneered "can't you read?" Bowles said. "They thought that I was drunk because I can't read 'left, right, up, down.'" 

"I think as a society, we tend to judge people by the way they communicate, and so naturally people sort of think that they're dumb or not smart," Brooke Lang, Bowles' speech pathologist, previously told Insider. But "all of that knowledge is still there, they just have trouble accessing the language piece." 

Aphasia has no cure, but speech-language therapy can help 

Aphasia is typically diagnosed via various physical and neurological tests and assessments, according to the Mayo Clinic. Doctors may order brain scans, ask patients to repeat words and phrases, and test their reflexes. 

There's no cure for aphasia, and treatment is typically speech and language therapy targeted toward each patient's particular challenges. The more intensive programs tend to be more effective, but they can cost upwards of $40,000 for six weeks, and aren't covered by insurance, Lang said. 

Emerging treatments include brain stimulation therapy, which aims to stimulate damaged brain cells, but long-term studies are still need on its effectiveness. Medications are also being studied as potential future aphasia treatments.