The symptoms you mentioned below are what made me think of TOS or possibly RSI/myofascial related conditions. Just related to those symptoms, not everything..
Generic PT plans usually do not help for those with TOS..or complicated and mixed diagnoses for that matter....standard PT can make it worse...

[Within the last 4 days I now have numbness down the back of my arm and into my ring and pinky finger and weakness in my grip. It causes forearm pain and weakness doing things if I end up trying to use my arm. This is problematic since it is my dominant arm. I have been in physical therapy since June but I think my therapist is just overwhelmed and doesn't know how to handle someone with such extensive numbness and trouble engaging some of my muscles which leads to challenges with trying to strengthen in PT (especially weakness in lower abdomen, lower leg, balance).
I do have neck pain/base of skull pain occasionally, but it is not too bad and not debilitating.]
[It is now impacting my ability to use my arm it is scaring me because I do not want to lose the ability to do my job. ]

Hey aeria,

Welcome to the Forum. I am so sorry to read about all your terrible experiences and symptoms.
My thinking, (on the same lines as Jomar) is that your hand/ arm/ finger symptoms are related to nerve entrapment and related to your neck base of spine issues.
I also note you have tight stomach muscles (and have ruled out GI tract issues) I just wonder if you would benefit from the use of a Foam Roller. Just lying on it appropriately would stretch your stomach muscles. Tight stomach muscles contribute to poor posture and poor posture may contribute to nerve entrapment by for example Upper Crossed Syndrome. I appreciate you have Ehlers Danlos Syndrome so this may not be valid but working on your neck shoulder area could at least reduce those classic arm/ finger symptoms that are very much associated with nerve entrapment.

Best wishes,
Atty

Welcome aeria.

If you've done research on MCAS, you know it can cause a raft of different symptoms, including neurological. What foods are you restricted from eating?

I believe that excess histamine is at the core of all my strange neurological symptom. You are the only other person I've heard describe this symptom I have..."episodes of numbness, itching and crawling sensation in my temple/scalp area." This is the first sign that I've eaten something I shouldn't. In short order, tinnitus sets in, and then a widespread vibrating/burning, rushing sensation that can run from head to toe. This usually lasts throughout the day and often impacts my sleep. The next morning, tinnitus will be the only lingering symptom, aside from the ever-present neuropathy in my lower legs and feet.

I'm still trying to figure exactly what substance or substances in foods I'm sensitive to. I believe salicylates are enemy number one, but given that I just found out I have a large kidney stone, oxalates are on the table too.

Just curious why and what do you do for it

Hi razzle,
9 Signs and Symptoms of Copper Deficiency

Copper deficiency is apparently pretty rare, but I asked aeria about their copper testing because of the list of symptoms they described.

Low copper has been associated with iron deficiency anaemia plus copper deficiency can be associated with neuropathy.

Also as far as I know, too much zinc can cause copper deficiency as well and in turn iron deficiency anaemia. A loop.

If you have anaemia caused by an acquired copper deficiency then you can change your dietary intake of copper rich foods.