Diego4Life, I'm sorry to say but your GP is wrong, a twitch is NOT a twitch. There are "true fasciculations" and then there are random muscle twitches, and there are even jerks, jolts, thumps and so on, all of which (except for true fasciculations for the most part) have NOTHING to do with ALS.
Now really, have you seen ANYONE on here GET ALS? Nope.
If "twitches were twitches", then why is it that random twitches do not show up on an EMG even when you are twitching while its being performed? It's because some are fired from nerves and some are "chemically" fired from things such as protiens, adrenaline and so on.
Just because a muscle movement occurs certainly doesn't mean they are occuring for the same reasons. That's like associating headaches with brain tumors and having a doctor say "a headache is a headache". That is just not correct.
You can have migrane headaches (for which they don't really know why the occur) yet), you can have a stress headache (which is caused by tense muscles), you can have sinus headaches (which are obvious why they occur), you can have a headache from lack of oxygen or chemical contact which depletes the oxygen levels in the brain), you can have all kinds of headaches of which NONE are any relation to the other and none have anything to do with brain tumors, just like you can have twitches, which none might have any relation to the other, ESPECIALLY ALS related causes.