Started with a stiff neck, spread down to left shoulder. deltoid area is swollen. pain is excruciating ache travels to elbow. paresthesia in hand, left rib and interior scapula pain. could this be pancoast tumor?

A Pancoast tumor is at the apex of the lung, and can present with symptoms of brachial plexopathy, but unless you have risk factors for lung cancer, it's unlikely. A chest X-ray would rule in or out such a diagnosis. An MRI of your cervical spine is appropriate, and would be next step in a diagnostic imaging work-up.

Not feasible to guess but maybe a brachial plexitis like Parsonage-Turner Syndrome or perhaps thoracic outlet syndrome. Could also involve shoulder joint See orthopedic or neurologist doctor