Having already survived breast cancer, WAFB-TV news anchor Donna Britt now knows the nature of her latest medical challenge.

The longtime local television personality has amyotrophic lateral sclerosis, or ALS, she announced Thursday afternoon. Britt has had muscle weakness for the past nine months and has posted updates on her condition on Facebook. But she did not have a diagnosis until three days of medical tests this week at the Houston Methodist Neurological Institute.

ALS is a progressive neurodegenerative disease that affects nerve cells in the brain and the spinal cord. Motor neurons reach from the brain to the spinal cord and from the spinal cord to the muscles throughout the body, causing the loss of muscle control, paralysis and, eventually, death.

Britt, 59, is using a wheelchair, according to WAFB. The disease has affected both legs, one arm and eight fingers, she said Thursday.

“Plans going forward are to meet each new challenge and master it,” Britt said. “Dr. (Sheetal) Shross says that how long I live depends on how well I can survive each new round of challenge. So, I plan to do every one.”

ALS also is known as Lou Gehrig’s Disease, named for the New York Yankees star who was forced to retire from baseball in 1939 at age 36 and who died in 1941. Other well-known people with ALS include former New Orleans Saints player Steve Gleason and English theoretical physicist and cosmologist Stephen Hawking.

Hawking is a rarity, having been diagnosed at age 21 and still living at 75. Most ALS patients are diagnosed after age 50 and die within five years, according to a 2012 Scientific American article about Hawking. Some patients, however, live 10 or more years.

Before Thursday’s diagnosis, Britt had been treated for chronic inflammatory demyelinating polyneuropathy, but said the treatment seemed to be making her worse. Unable to get an appointment at the LSU Health Sciences Center in New Orleans, she was able to see ALS experts directed by Dr. Stanley Appel in Houston.

The diagnosis was not a total surprise. Britt said her mother’s brother had ALS, and Britt thinks her grandmother may have died of ALS but was misdiagnosed.

Britt, who has a bachelor of music education degree from LSU, has worked at WAFB since 1981. She was diagnosed with breast cancer in 2008. The cancer was discovered early and responded to treatment.

She has been recognized as Communicator of the Year from the Public Relations Association of Louisiana, received a Lifetime Achievement Award from the Louisiana Association of Broadcasters, an Award of Excellence from Women in Media, and a Volunteer Activist Award from the Emerge Center.

Britt said she will continue working as long as she is able. The disease does not affect her brain, she said.

“I’m going to continue working because these are my friends, and I do believe that it is important for you to be happy, and when I can work with my friends and feel productive, I’m a happy person,” Britt said.

Britt is married to Advocate Capitol Bureau chief Mark Ballard. Their daughter, Annie, is a scientist working in the DNA research industry, and their son, Lou, is in high school.

Follow George Morris on Twitter, @GWMorris.