Here are my answers that I got from my 2 neuros after EMG:
1) ALS twitches never start on the whole body. If so, then there were unoticable twitches before - thats the main difference. The people who think they had wide-spread twitches at the one time, those people didnt notice slight twitches before. Its due to the pathology of the disease, it canf affect the whole neuromuscular system at once, its progressive
One exception: Suspicious are rare twitches (a few per hour) in absolutely different places. Bening twitches have mostly "hotspots" and are more frequent.
2) ALS twitches are often slighter, less noticable than benign ones. However, this isnt reliable
3) ALS twitches never come and go. If the muscle starts to dying, it twitches. When the twitching stops, the muscle is dead/inactive. Twitching can change its intensity, but never disappear fully.
4) ALS twitches can be recruit by tapping on the muscle/stretching it. Bening ones too, but only rarely and only first time the muscle is stretched.
5) Twitching CAN be earlier than weakness/atrophy, because its the moment when the muscle is affected. The weakness must follow in a 1-4 weeks or its present.
I dont say these have to be valid for all, as the neuros said: these facts are same for all, but some people didnt notice slight twitches, some of them didnt notice weakness in muscles they dont use much and so on..this lead to many variations.