Answer:
In BFS, the fasciculations only occur when the muscles are at rest. In ALS, they are consistent. Even when you walk, you will have the fasciculations. And ALS is characterized by severe muscle weakness. A fasciculation is a small twitch in your muscles, like your muscle going up and down in like a heart beat.
In ALS you would have weakness or atrophy/weakness.In BFS you would not.Fascis in both can look,feel and last exactly the same.FASCICS MEAN NOTHING if you have no severe,and i mean no other severe symptoms.So to answer your question you cannot tell by looking at them.