text_1: This morning I saw a 70-year-old man with left-sided shoulder pain and numbness.  His biceps and triceps were weak and he had atrophy of his triceps.  Got cortisone injection by orthopedist 2 weeks ago with no improvement, normal x-rays.  High dose nonsteroidal anti-inflammatory drug no help. I didn't know what to make of it.  Neuropathy?  I called a neurologist and ended up referring him.
text_2: What is causing this 70-year-old man's left-sided shoulder pain and numbness?