It usually follows some type of stress situation, such as surgery, childbirth, trauma, or simply a cold or flu-like illness. The cause is unknown, but thought to be related to an autoimmune or viral attack on the nerves of the brachial plexus. Pain is the foremost presenting complaint, but weakness and atrophy of muscles of the arm is generally present as well. Luckily, most of the arm usually recovers, but small but significant deficits can remain. Depending upon the type of deficit, nerve surgery involving nerve transfers or releases is sometimes helpful.
Tendon transfers are sometimes necessary in severe deficits.
I have taken care of several patients with this injury, and believe that surgery is usually not necessary, but helpful in specific selected situations. Your particular symptoms should be investigated to rule out a nerve compression such as carpal tunnel syndrome which might be present in addition to your recovering brachial neuritis.