what is causing the numbing tingle in my left arm?

There are a variety of causes that might be responsible for this pain. Have you had it long? Do you have any back issues?

I was having tingling in my arm; went to a neurologist who performed an EMG. Turned out he found some nerve entrapment at the elbow. He told me to get one of those elastic braces that kept me from bending the elbow when I slept. I still have some tingling if I lean on that elbow when sitting in a chair too long.

It also could be an issue with a pinched nerve in your upper back. Those are 2 possibilities I can think of....

I have many disks that are effected by degeneration. I've had surgery on my C5&C6 to fuse them together. I also have had many cortizone shots to reduce the pain of three herniated disks. When I lean my head foreward, just abit, my left arm gets a numbing tingle all the way down to my finger tips. It's annoying. Thank you for you response.

C4, C5 and C6 are the levels that affect the areas of your arms...so it is possible you have a disc that is bulging or otherwise causing the nerve to be pinched, or compressed. You can look for information on dermatomes to learn more.

You'll want to check out the Spinal Cord Disorders board....we discuss more cervical stuff over there (most here is lumbar).

I had similar symptoms before (and now after) my ACDF.