After battling multiple sclerosis for decades, Annette Funicello died today from complications of the disease.

That doesn’t mean that MS actually killed her, says Dr. Rhonda Voskuhl, a professor in the department of neurology at the University of California, Los Angeles and director of the UCLA MS program.

“MS does not directly shorten the lifespan,” Voskuhl explains. “It doesn’t kill people directly. If you’ve had a very severe form for a very, very long time you can have the same complications that anyone has who is immobilized. You can get pneumonia. You can get bed sores. You can have difficulty eating.”

These days the prognosis for the vast majority of MS patients is better than it was when Funicello was diagnosed because there are treatments that can slow the progression of the disease. “There was a revolution in MS drugs in the late 90s,” Voskuhl says. “Those drugs don’t stop the disease, but they slow it down.”

If you were diagnosed years ago, before there were good treatments, many brain cells could be lost.  “Early treatment is very important,” Voskuhl says.

No one understands exactly why MS strikes some people and not others. But in some, the immune system goes out of whack and begins to attack the outer covering of axons, which are the structures that function like phone lines to carry information from cell to cell in the brain.

In people with MS, immune cells chew away at the axons’ outer covering, or myelin, and that makes signals ragged. The situation is similar to a phone line with a damaged rubber coating: Voices sound ragged if the damage is minor, an unintelligible if it’s worse.  

There’s a wide variation in the type of symptoms people experience with MS. Some just feel odd sensations, like tingling, or lose feeling in body parts from time to time.

Some develop cognitive deficits. “It’s not like Alzheimer’s,” Voskuhl explains. “It’s not like everyone knows you have it. Generally the patient knows. It’s usually involves problems with processing speed. They can’t think as quickly as they used to.”

And some end up with problems moving, like Funicello did. It all depends on what area of the brain is attacked.

As it turns out, the kinds of symptoms a person experiences early on may give doctors a clue as to whether the disease will be aggressive or mild. “In that respect, it’s better to have sensory symptoms than motor problems or balance issues,” says Dr. Clyde Markowitz director of the MS Center at the University of Pennsylvania.  

While the new drugs don’t repair damaged axons, they do quiet down the immune system so there are fewer attacks.

Had Funicello been born a decade or so later, there’s a good chance that her disease might have taken a different course, experts say.

“She was diagnosed at a time when we didn’t have any therapies available,” Markowitz says. “We see much less of that guaranteed progressive phase now.”

Heart wrenching videos of Funicello in her later years show a woman trapped within an immovable body. It’s quite possible that Funicello remained cognitively intact even as her body was failing her, says Dr. Rock Heyman, director of the Pittsburgh Institute for MS care and research at the University of Pittsburgh Medical Center. “I have seen patients who are unable to move their arms or legs that are still intellectually active.”