Former Chicago Bears lineman William "The Refrigerator" Perry remains hospitalized with a rare nerve disorder that can slowly paralyze a person, starting at the fingers and toes and moving in towards the limbs, torso and face.
Known as the "The Fridge" for his robust physique -- 6 feet 2 inches tall and 370 pounds -- the retired football player was in serious condition today at Aiken Regional Medical Center in South Carolina, according to the Associated Press.
Aiken Regional Medical Center did not return messages from ABCNews.com.
Adam Plotkin, Perry's agent, said the athlete checked into the hospital last week.
"He was in there last year [too]; that's when he was diagnosed," said Plotkin. "He is significantly improving."
Plotkin said Perry is recovering well, but many are confusing Perry's condition, called Chronic Inflammatory Demyelinating Polyneuropathy, or CIDP, with the fast-acting and sometimes-deadly Guillain Barre Syndrome.
Both conditions are rare. CIDP affects about 5 out of 100,000 people and Guillain Barre Syndrome affects 2 out of 100,000 people worldwide.
"They can have the same manifestations ... but the time course is different," said Dr. Kenneth C. Gorson, professor of neurology at Tufts University School of Medicine and a neuromusuclar specialist at St. Elizabeth's Medical Center in Boston.
"The CIDP patient will come into the office and tell you, 'I've been getting progressively weak. I had trouble walking, trouble with balance. Then I needed a cane and now I can't walk,'" said Gorson. The symptoms of CIDP, which Plotkin said Perry has, develops over at least eight weeks or longer.
But, the course of nerve damage in Guillain Barre Syndrome happens much faster.
"It can be as mild of some just tingling in the face or numbness in the hand," Gorson said of Guillain Barre Syndrome. "But the most severe cases go from completely normal to completely paralyzed on a ventilator within 48 hours."
First described by two French physicians in 1919, doctors now know Guillain Barre is often triggered after a viral infection, a vaccination or a bacterial infection in the intestine.
"In the process of our immune system reacting to it [a viral or bacterial infection], there's cross reactivity where we begin to react against ourselves," said Dr. David Cornblath of Johns Hopkins University in Baltimore.
Yet doctors say there are many more unknowns for both CIDP and Guillain Barre. For instance, Gorson said doctors do not know what triggers CIDP.
As for Plotkin, he said he has been frustrated by the confusion with Guillain Barre, and he said Perry's serious condition is not as serious as it seems.
"I've heard rumors he is on his death bed and he's not," said Plotkin. "He appreciates the support of his fans, and he'll be back new soon."
Indeed, Gorson said CIDP often is treatable and the paralysis is reversible, but patients can unexpectedly relapse after what appears to be a successful recovery.
"We're not certain of the mechanism of action," said Gorson.
In the case of CIDP, the body mistakes lining on nerves, called myelin, as a foreign invader -- and the immune system attacks the nerves causing symptoms of numbness, tingling and can eventually lead to rapidly progressive paralysis.
Patients can reverse the symptoms with an infusion of antibodies from donated blood called intravenous immunoglobulin or IVIG.
"Fundamentally, we think in some way it neutralized the abnormal antibody and allows their nerves to heal," said Gorson.
Gorson said the antibody infusions for CIDP also can be used to treat and cure Guillain Barre Syndrome, although the two syndromes probably have different causes.
"CIDP is an unpredictable condition," said Estelle Benson, founder and executive director of GBS/CIDP Foundation International.
"You never know how much is going to be damaged, how long it will take, how much [movement] you're going to take back," she said.
Benson first heard of Guillain Barre and CIDP after her husband fell sick with a cold.
"He had a bad cold and a week later he was completely paralyzed," she said.
Later, he was diagnosed with Guillain Barre Syndrome and eventually recovered.
But Benson was determined to bring sufferers from the two very rare diseases together.
"We started with eight people in the house and now we have 30,000 people, 160 chapters around the world," said Benson. "We've had people call from Ethiopia and Kenya with it."