I don’t know and you’re not going to find a definition here, obviously you can Google it or look on Wikipedia if you want the details. I already know more just by getting those links for you such as it’s also know as MND, or at least a type of it.
Let’s be honest most of us would never have heard of ALS if it wasn’t for everybody poring ice water over themselves. I’d like to encourage you to watch this YouTube clip of someone with ALS who does his challenge, but then gives you a peek into the life of a sufferer. It’s scary and that’s only a peek, he has to live with that day after day after day.
So please had a look and see why all these folks are getting cold, because what people go through is in some ways more important than the clinical definition.