By Dr. Albert Fenoy,
Director, Deep Brain Stimulation Program
Associate Professor, Department of Neurosurgery
McGovern Medical School
The University of Texas at Houston
Patients with essential tremor (ET) usually present with hand tremor, an involuntary shaking of the hands dependent on position. However, head tremor can also develop in the course of ET or present as a singular symptom. ET is the most common cause of head tremor. Cervical dystonia, or spasmodic torticollis, is another less common cause. Patients with Parkinson’s disease can also develop head tremor.
Dysfunction of circuits in the brain are thought to be the mechanism for essential tremor. It is proposed that the ventrointermediate nucleus (Vim) of the thalamus, deep in the brain, plays a key pacemaker role in this disease. If an abnormal rhythmic output develops in deeper structures that connect to the Vim, such as in the cerebellar dentate nucleus or inferior olivary nucleus, an abnormal signal travels downstream through the red nucleus to the Vim and motor cortex via the dentato-rubro-thalamic tract (DRTt), manifesting as tremor.
The vast majority of patients with ET present with hand tremor. However, about a third of ET patients have head tremor by itself or with hand tremor. Head tremor can also develop in ET patients over the length of their disease, as severity of other tremor increases. Voice tremor can also develop over time. In ET, hand tremor is postural, occurring with action resisting gravity such as holding objects away from the body. Stress can intensify tremor. Parkinson’s disease tremor, conversely, is found in the hand usually at rest, and can also occur in the lip or jaw. Patients with Parkinson’s disease have slowness of movement, muscle rigidity, and gait difficulties that are not seen in ET.
Cervical dystonia is another less common cause of head tremor. Dystonia is another disease due to an abnormally functioning circuit in the brain. Here though, this circuit causes abnormal muscle tone which in turn causes muscle spasm and abnormal posturing. In the case of cervical dystonia, the sternocleidomastoid muscle is usually affected more on one side, becoming much larger with spasm, leading to an abnormally sustained neck posture or torticollis. The neck muscular spasms can cause head tremor. Cervical dystonia can occur in isolation or over time become generalized over the body. It is usually associated with neck pain due to muscular spasm, which is unlike ET.
Sensory tricks such as touching the cheek or chin (geste antagoniste) is a common remedy used by patients with cervical dystonia to lessen the severity of the tremor. Also, as there is asymmetry to the neck, there typically is a preferential direction for a patient to look or a specific position to adopt to reduce the tremor and the pain associated with it.
It is important to properly diagnose the tremor so a proper treatment plan can be prescribed. This is performed clinically, however, imaging of the brain is performed to rule out structural lesions such as stroke, multiple sclerosis or tumor. A DaTscan can be ordered when it is unclear if the tremor is due to ET or parkinsonism; as a DaTscan targets the dopamine transporter which is deficient in parkinsonism, a normal level is found in ET. Blood tests can be performed to rule out hyperthyroidism or Wilson’s disease.
Treatment of head tremor in essential tremor usually starts with medication such as propranolol and primidone, and can also include gabapentin and topiramate. It is more difficult to control than hand tremor. In cervical dystonia, treatment usually starts with benzodiazepines and baclofen. Botulinum toxin can also be used to reduce head tremor when applied to spastic head muscles, such as the sternocleidomastoid, in cervical dystonia. As these toxins block the release of neurotransmitters, the muscles stop contracting, thereby reducing spasms and tremor. However, it usually is not fully effective and must be repeated every three months.
Deep brain stimulation (DBS) surgery is a more invasive option to treat tremor and is promoted when conservative measures fail. Introduced in 1987, it became FDA approved in 1997 for the treatment of tremor and 2003 for treatment of dystonia. It has thus been used for over 30 years with a very high success rate, decreasing tremor in individuals by 80-90%. As it is an invasive procedure, the procedure does carry a risk of bleeding or infection, at about 1-2%. Electrodes are placed in the brain at a node in an abnormally functioning circuit to normalize its firing. In the case of ET, the electrode typically targets the Vim or the DRTt. In dystonia, the target is typically the globus pallidus internus. Unlike hand tremor, head tremor can be difficult to control with medications alone and so sometimes DBS is the best treatment option.
Not every person with ET may have head tremor, or vice versa. If you do have head tremor, it is important to talk to your physician – not only for the correct diagnosis, but also to find the best treatment option available.