723.4 Brachia neuritis or radiculitis NOS which can include cervical radiculitis, or radicular syndrome of upper limbs. It means there is inflammation of the nerves of the upper arm(s) that causes weakness and pain.
Since 723.4 is a symptom rather than a disease, the first thing should be to find out what is causing the neuritis (infectious process vs nerve impingement vs overuse, etc.). If no cause is found (often it isn't) then symptomatic treatment is all that is done. This may involve antidepressants, drugs used for peripheral neuropathy (Lyrica, Neurontin), and pain medication.