An uncontrollable shaking of the arm is referred to as a tremor and can be caused by medical conditions such as stroke and multiple sclerosis, according to MedlinePlus. Tremors can also occur in individuals with brain injuries and as a reaction to alcohol withdrawal.
Individuals with Parkinson's disease and liver failure may also experience tremors, according to WebMD. Tremors can be brought on after taking medications such as antidepressants and lithium. It's important for individuals with uncontrollable shaking of the hands, arms, feet, legs or torso to seek medical attention to ensure a proper diagnosis. Treatments for tremors include medications and brain surgery.