Bruce Willis' decision to end his acting career of more than four decades after a recent aphasia diagnosis has put a spotlight on the somewhat rare disorder.

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 United States, and nearly 180,000 acquire it each year, according to the National Aphasia Association.

The most common cause of aphasia is brain damage from a stroke, though it can also arise as a result of a head injury, brain tumor, infection.

According to the National Institutes of Health aphasia is caused by damage to one or more areas of the brain that deal with language.

According to the National Aphasia Association aphasia’s symptoms vary, as can their severity, in the most serious cases, communication with the patient almost impossible.

Aphasia can be treated and reversed if the cause is caught early, patient suffering from aphasia might regain the ability to speak.

Bruce Willis, an Emmy-winning actor and star of hit movies like "Die Hard" and "The Sixth Sense," turned 67 this month.