First of all, it's great that you're asking so many questions! Knowledge is power when it comes to the diagnosis and treatment of TOS. You will find that this can be a controversial area in medicine (a function both of the difficulty in accurately dxing TOS and rather poor surgical outcomes in the tx of many neuro cases [the stats are much improved for vascular - venous, arterial or both - surgical TOS cases]), and that very few choose to specialize in TOS.

There are also many "TOS deniers" who do not believe that neurovascular entrapment can occur at the level of the thoracic outlet. So be sure before you go in for any appointments that the physician you are seeing actually specializes in, or at least treats, TOS. You don't say what part of the country you are in, but hopefully you will have some luck with our sticky of TOS docs and PTs. TOS can imitate several other syndromes, so the most common way of getting accurately dxd is clinical. It is not uncommon at all for a whole gamut of different types of tests to come back "negative." This in and of itself does not mean you don't have TOS.

I have what used to be called "true neurogenic TOS" (as opposed to "disputed" neurogenic TOS), where there is severe and very noticeable atrophy of certain intrinsic muscles of my hand/s - and believe it or don't it still took almost 30 years for me to get the dx. Ultimately, I was dxed clinically by a top TOS vascular surgeon. Experienced pain management docs (particularly those with a background in neurology or physical medicine) can also be good at dxing this complex disorder. TOS is not an orthopedic problem. The best txment team you can put together would probably include a neurologist, a vascular surgeon and a PMP. A TOS-savvy PT (they're not easy to find sometimes…) and/or bodyworker can be your best friend.

As far as sleeping positions go, sleeping on your stomach is an absolute no-no (it will only exacerbate your neck pain [a very TOS - like sx, by the way]). If side sleeping is out, can you sleep on your back? Many of us use bolsters or extra pillows to prop ourselves up with at night for sleep. And there are many more, especially after TOS surgery, who find they must sleep in a recliner.

The "culprit muscles" in TOS are usually the pec minor, the subclavius and the anterior, middle and any relic scalene muscles you may have. Every TOS case is different, and every doc has their own regimen of clinical findings and tests to determine whether you have TOS and what type. You may need a 3-d CT scan to determine, for example, whether yours is a soft tissue or a "bony" case - which might determine what type of TOS surgery is indicated, if any (a rib resection, a scalenectomy, both, and/or a pec minor tenotomy). Years ago, a simple scalene block was a favored way to rule TOS in or out; these days your surgeon may use other measures.

TOS can be caused by accident (like whiplash), by injury or by congenital anatomical differences like cervical ribs or fibrous bands transversing the brachial plexus off a C-7 nerve root. My case had an insidious onset, just like yours. It happens.

Lastly, my doc sometimes has to take my blood pressure at the ankles due to the fact that there is so much neurovascular compression or injury that an accurate reading cannot be made from either arm. I think you and I might be kindred spirits!

Sorry to ramble; hope this helps a little bit. Good luck and I hope you find some answers soon.

PS. Tshadow did a thread on TOS testing you might want to find using the search function on this forum.