found this good reading:Is a spasm just a severe type of tremor?
: Dealing with Tremor
Types and causes of tremor
Tremor, defined as an involuntary rhythmic shaking of a body part, affects between 25% and 60% of people with multiple sclerosis (MS). MS tremor tends to affect the limbs, the head and neck, the vocal cords, and the trunk of the body. It can interfere with the ability to do everyday activities such as speaking, swallowing, writing, and walking.
It's difficult for scientists to tell exactly why people with MS experience tremor. Because MS affects so many different parts of the brain, it's hard to link the tremor to a single damaged area. However, they do know that MS tremor results from MS-related damage to areas of the brain that control movement.
People with MS may experience a variety of different kinds of tremors. The most common type of tremor in people with MS is intention tremor. Intention tremor occurs only during movement, not when a person is at rest. Intention tremor develops and gets worse as the person tries to move their body parts towards a specific target (e.g., reaching for objects, writing). It is worst during small, intricate movements, such as those needed for handwriting.
Postural tremor is a type of tremor that occurs when people are trying to support their own weight against gravity. This means it would not occur when a person is lying down, but it could happen when they are sitting or standing.
Rest tremor is not common for people with MS. This type of tremor occurs when someone is at rest. In other words, it happens when they are not moving a body part or supporting it against gravity.
Nystagmus is a type of tremor that affects the eye muscles, leading to uncontrolled eye movements.
MS tremor can range from mild to severe. When tremor is very severe, leading to large back and forth motions of the affected body part, it is called gross tremor.
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