By Jean P. Hubble, M.D.
The diagnosis is usually quite obvious – rhythmic shaking of the hands. Despite the fact that essential tremor (ET) is common and easily recognized, there are many aspects about the clinical presentation which are poorly understood.
Virtually all individuals with ET have tremor of the hands. The next most frequently affected body area is the head and voice. Head and voice tremor occurs in about 30% of ET patients in most reports. It is possible that age, duration of the tremor disorder, or gender might be predictive of the clinical expression of ET, including affected body region. To test this notion, we conducted a study at the University of Kansas Medical Center Tremor Clinic in 1992-1995. The results of this work were reported in the journal Movement Disorders, 1996, Volume 12, pages 969-972.
Clinical information obtained from 450 ET patients was analyzed. The average age was 67 years while the average duration of tremor was 25 years. There were 232 men and 209 women included in this analysis. Nearly all of the study subjects including men and women had tremor in the hands. However, only 30% of the men had tremor affecting the head and voice while 60% of the women had tremor of the head and voice. In addition, hand tremor was more severe in men and head and voice tremor was more severe in women. Thus, women were more often affected by tremor of the head and voice and had more severe head and voice tremor compared to men. There is no ready explanation for this finding. It is possible that the sex chromosome (X<Y) influence the expression of tremor in men compared to women.
Alternatively, the sex hormones (estrogen, progesterone, and testosterone) may influence the location and severity of tremor in some way. Another explanation for these findings is that women with tremor may have another neurological symptom called “dystonia.” Dystonia refers to involuntary, sustained muscle contractions which can cause unusual postures including head turning. It is possible that some of the head tremor in subjects participating in the study was due to dystonia of the neck (torticollis). In contrast to gender, age and duration of tremor did not distinguish those individuals who had tremor affecting the head and voice from those who had hand tremor only.
Unfortunately, there are few effective remedies for head and voice tremor. Sometimes, the conventional tremor medications will help suppress head tremor to some degree. These medicines include propranolol, primidone, and clonazepam. Botulinum toxin injections into the neck muscles may help suppress head tremor. However, botulinum toxin injections can result in transient muscle weakness so that the patient who undergoes injections may have difficulties with head droop or difficulties with swallowing for several days or a few weeks. Botulinum toxin injections may help voice tremor when it is associated with dystonia of the vocal cords (muscle contractions of the vocal cords). Deep brain stimulation of the VIM nucleus of the thalamus has been shown to improve head and voice tremor in some patients.
Part of the limitation in our ability to better treat tremor is due to the fact that the causative brain mechanisms for tremor are not precisely understood. It is possible that a better understanding of the brain chemistry in ET will lead to better treatments.
By Jean P. Hubble, M.D.