Why My Left Thumb Feels Strange, Almost Cold When I Stretch Out My Fingers?

Question: Hi,

I am a 37 year old man. About six months ago my thumb started to twitch when I was holding a book. I ignored it, but about a month ago the twitching suddenly got worse, and spread to my forefinger. It usually occurs in my left thumb and forefinger, although it has occurred in my left arm and leg. It is a postural tremor and also an isometric tremor which happens after I apply a bit of pressure or am holding something in place. For example, if I am leaning on my hand, or lie down with my hands behind my head. That is when it twitches the most. Most of the time the twitching goes for less than a minute then stops. Also my left thumb feels strange, almost cold when I stretch out my fingers all the way with my hand in an L shape. I also get random spasms all over my body. My right foot started to twitch for about 2 hours straight last night. I couldn't sleep.

I went to a doctor and she said I might have benign fasciculation syndrome, but the twitching is getting worse and I am terrified of ALS.