I think this is a interesting article, I found it years ago but had lost the link to it.
Four major syndromes have specific characteristics and diagnostic tests

by Elaine Wallace, DO

[TOS Classifications
The syndromes of the Thoracic Outlet are easily subclassified according to the symptoms of the structures compressed – artery, nerve, vein, or lymphatic.

and more
Scalenus Anticus Syndrome
The Scalenus Anticus Syndrome involves a compression on the brachial plexus and/or the subclavian artery as these structures pass through the interscalene triangle. Pressure is usually imposed by muscle hypertrophy.

Usually, it is the posterior portion of the brachial plexus (i.e. the ulnar nerve) that is involved in this syndrome so symptoms of neuropathy most often involve numbness in the fourth and fifth fingers, the lateral side of the hand and possibly the forearm, and decreased sensory appreciation of light touch or pinprick in the 5th digit.]

the whole article-
http://www.osteo-france.net/FREtude%201.htm