I was diagnosed with Chiari Malformation 1 after years of having issues, but one of the major symptoms I have are tremors in my hands and neck, the worst is my neck. I have a neurologist now (as I was diagnosed finally in July of 2021) who started giving me botox in my neck (cerebellum down to my shoulders), right side of my neck, and face (twitches), and it really really eliminated the majority of the tremor/twitches I get. It's hard because doctors don't fully understand Chiari, but the spasms definitely stem from the Chiari. I want to find a hospital near that specializes in Chiari, as most doctors don't really have all the answers, you may want to find one who specializes in or is experienced with Chiari Malformation. Chiari also causes me dizziness, confusion, (newer that I notice) higher blood pressure, and blurred vision at times (when it's triggered/herniating). This is just based on my personal experience so far and things the neuro went over with me.
It is possible it is related to Chiari or Syringomyelia....as either of them can affect different nerve endings which could cause the twitching. I had restless legs for a while around the time I was DX...but I only have it on rare occasions now....Is your Dr a Chiari specialist?