<unk>  <unk> , also called benign<unk> , familial<unk> , and idiopathic<unk> , is a medical condition characterized by involuntary rhythmic contractions and relaxations (oscillations or twitching movements) of certain muscle groups in one or more body parts of unknown cause. It typically is symmetrical, and affects the arms, hands, or fingers; but sometimes involves the head, vocal cords, or other body parts.<unk>  is either an action (intention)<unk> —it intensifies when one tries to use the affected muscles during voluntary movements such as eating and writing—or it is a postural<unk> , present with sustained muscle tone. This means that it is distinct from a resting<unk> , such as that caused by Parkinson's disease, which is not correlated with movement.<unk>  is a progressive neurological disorder, and the most common movement disorder. Its onset is usually after age 40, but it can occur at any age. The cause is unknown. Diagnosis is by observing the typical pattern of the<unk>  coupled with the exclusion of known causes of such a<unk> . While<unk>  is distinct from Parkinson's disease, which causes a resting<unk> ,<unk>  is nevertheless sometimes misdiagnosed as Parkinson's disease. Some patients have been found to have both<unk> s and resting<unk> s. Treatments for<unk>  include medications, typically given sequentially to determine which provides the best compromise between effectiveness and troublesome side effects. Clostridium botulinum toxin (Botox) injections and ultrasound are also sometimes used for cases refractory to medications.
Essential tremor
Dystonia
Holmes tremor
Intention tremor
Myoclonic dystonia
Multiple sclerosis
Focal dystonia
Parkinson's disease