Dr. Jon LaPook joins "CBS Mornings Plus" to explain normal pressure hydrocephalus, the rare brain condition impacting Billy Joel's vision, balance and memory, and why it's often mistaken for Alzheimer...

The 76-year-old singer was diagnosed with Normal Pressure Hydrocephalus (NPH), according to a statement on his website.

"This condition has been exacerbated by recent concert performances, leading to problems with hearing, vision, and balance," the statement said.