could numbness and subjective weakness in left arm and hand be caused by a pinched nerve?

My left hand and arm abruptly went numb and weak, along with lightheadedness, when I was reaching to do something. There was no pain. The weakness and dizziness went away about ten seconds later, and after three days, my arm and hand still have mild-to-severe persistent numbness, though it is steadily improving. There were no detectible stroke or mini-stroke symptoms. EKG and CT scans showed nothing; MRI won't be for a week. I have always had stiff muscles in my back and below my neck. The neurologist I went to immediately dismissed a brachial plexus injury, based on the same information as here (possibly because he is a neurologist). I am not so sure. Any help would be appreciated.