(CNN) — Civil rights leader Rev. Jesse Jackson has been hospitalized, according to a statement obtained by CNN.

Jackson, 84, a protégé of the Rev. Martin Luther King Jr., is under observation for progressive supranuclear palsy (PSP), the Rainbow PUSH Coalition said Wednesday evening.

“He has been managing this neurodegenerative condition for more than a decade,” the organization said in the statement.

“He was originally diagnosed with Parkinson’s disease; however, last April, his PSP condition was confirmed. The family appreciates all prayers at this time.”

Further details about his condition have not been released. However, there has been “significant improvement” in the civil rights leader’s condition over the last 24 hours under medical care, his son Jesse Jackson Jr. said Thursday in a segment during his weekday radio show.

“On behalf of the Jackson family, we cannot extend enough of our gratitude for those of you who have expressed your thoughts and prayers,” he said on his KBLA show, “The Jesse Jackson Jr. Show.”

PSP is “a rare neurological disorder that affects body movements, walking and balance, and eye movements,” according to the US National Institute of Neurological Disorders and Stroke.

The disease typically begins in a person’s 60s and has some symptoms similar to Parkinson’s disease, it adds. Most people with PSP develop severe disability within three to five years.

Jackson’s son said he started receiving text messages from his mother towards the end of his radio show on Wednesday, sharing that his father “was not having a good day.” By the time he got to him, his father was already in the ambulance, with police and the fire department at the scene, Jackson Jr. said on his show.

“I jumped out of my car and jumped into the ambulance and rode to the hospital,” Jackson Jr. said. “The doctors were able to work on him to get him the necessary fluids he needs to sustain him.”