Intention Tremor, also known as Kinetic, Action and Cerebellar Tremor, is a condition where goal-directed movements produce shaking in the moving body parts - most noticeably in the hands.
When you move your finger to perform a fine task, for example putting a key in a lock, you tell your arm muscles to move by sending nerve transmissions down the motor nerve pathways. The brain gets feedback about the movement from sensors in the joints and muscles which it uses to control the movement and gently guide the key into the lock.
People with intention tremor get the feedback more slowly, send corrective transmissions to the muscles more slowly, process the whole thing more slowly in the cerebellum (the part of the brain responsible for coordination) or any combination of the three. This makes the hand constantly overshoot the target resulting in tremor. Intention Tremor is more obvious when performing delicate fine movements than broad sweeping ones.
Intention Tremor is quite common in Multiple Sclerosis though it is associated with a number of other conditions including Parkinson's disease, trapped peripheral nerves and some drug treatments. Intention Tremor is related to Ataxia and in MS it is often caused by lesions in the cerebellum.
Intention Tremor is commonly detected by neurologists using finger to nose tests. The neurologist holds up his or her finger and you move your finger from your nose to his or her finger and back to your nose.
Intention Tremor is quite difficult to treat - Isoniazid, Zofran (Ondansetron), Propranolol and Primodone are drugs that have been tried with moderate results. Some people with MS find that cannabis is effective for tremors. Physical Therapy is often useful and wearing wrist weights can often mask out the effects.
Deep Brain Stimulation with a "gamma knive" (focused radiation) to stimulate or destroy parts of the brain (particularly the thalmus) has been tried in Parkinson's Disease and Multiple Sclerosis. Such options are radical and only used as a last resort for very severe tremors which do not respond to other treatments.
NINDS Tremor Information Page
Classification of Tremor and Update on Treatment
The many forms of tremor