I have treated this condition… a lot, for many people, and have taught graduate courses on this.
It is similar to sciatica, which originates from lower back, but caused by a number of factors. I lower back it comes from bulging lumbar discs, arthritic spinal stenosis, strained sacro-iliac joint, or tight hip rotator cuff.
Brachial plexus neuritis is pretty much the exact same thing, but originating at the neck. Starts out as mild but sustained pressure anywhere along the course of the nerves… anywhere from cervical spine to the carpal tunnel at wrist. Mild squeeze causes entire length of nerves to swell slightly, but enough to compress nerves anywhere they pass through tight spaces at neck muscles (scaleni), pectoral muscles, passing over top rib, elbow, forearm, wrist. Often multiple sites flare up, mimicking tennis elbow, golfers elbow, and carpal tunnel syndrome. The arm symptoms are nasty but NOT the root of the problem.
Aging reduces thickness of discs at cervical spine, causing bones to close down on nerves leaving spinal cord and headed for arm. That is usually the origin of the problem and… yes… gentle at-home cervical traction, neck posture tactics, and stretching are shown to be the best treatment… correcting the mechanical causes at neck. This includes correcting how you posture your head, neck, shoulders during driving, computer work, driving, fine hand tasks. I will post link to my ebook on self-care of neck-arm pain disorders.
Can be highly disabling and can create secondary disorders such as carpal tunnel syndrome, radial tunnel syndrome (mimics tennis elbow), cubital tunnel syndrome (mimics golfers elbow). That is why treating the neck is vital to treating arm-hand over-use pains.