Muscle spasms, twitches in arm upon throwing · Dx?

Involuntary upper right arm muscle contractions and spasms, which began intermittently when the patient was a teenager, were now a real problem for him as an adult. The patient was having difficulty rolling a baseball underhand to players as part of infield practice and he was experiencing muscle spasms when lifting his right arm over his head. "Twitches" in the patient's upper arm were making drinking difficult, but he had no problems feeding himself, writing, or performing other basic activities of daily living.