What is the cause of essential tremor?

Idiopathic tremor (ET) is the most common movement disorder, mainly postural and athletic tremor of hands, head and other parts of the body. Essential tremor has contradictory clinical essence. On the one hand, it is a mild single symptom disease, on the other hand, it is a common progressive disease with significant clinical variation. The tremor of this disease is aggravated by concentration, mental stress, fatigue and hunger. Most cases disappear temporarily after drinking and get worse the next day, which is also the clinical feature of essential tremor. The etiology of essential tremor is not clear, which is easily confused with tremor caused by other diseases.

Idiopathic tremor is also called familial tremor, and about 60% patients have family history. Many families with primary tremor have no modern phenomenon, and the gender distribution is balanced. Generally speaking, this is an autosomal dominant inheritance, which was completely revealed before the age of 65~70, and some cases of incomplete exposure and sporadic cases have been reported. The clinical characteristics of sporadic and hereditary populations are completely consistent, and they are usually considered to be the same disease, but the related genetic abnormalities have not yet been determined. The bimodal characteristics of onset age of essential tremor suggest that there may be two different abnormal genes. The onset age of familial tremor is earlier than that of sporadic cases, suggesting that early-onset essential tremor is more influenced by genetic susceptibility, and genetic susceptibility obviously affects the clinical subtype characteristics.

The exact cause of the disease is still unknown. It may be the result of the interaction between peripheral muscle spindle afferent and central autonomous oscillator. The ventral intermediate nucleus of thalamus (VIM) is a nucleus receiving proprioception, and the rhythmic burst discharge activity of its neurons may play a key role, which has been confirmed by electrophysiological records and stereotactic surgery. The PET study of CO2 labeled with oxygen (15O) showed that the metabolic function of bilateral cerebellum and inferior olivary nucleus was hyperactive. Functional magnetic resonance imaging (FMRI) showed that the contralateral cortical movement and sensory area, globus pallidus and thalamus of the affected limb were enhanced, and the bilateral dentate nucleus, cerebellar hemisphere and red nucleus were hyperactive. These results show that tremor is the result of the oscillation of cerebellum-olivary nucleus loop in thalamus and motor cortex to spinal cord pathway. Because there is no specific change in pathological anatomy, the position of abnormal vibration pacing point in the central nervous system is not clear, so it is speculated that the central oscillator can enhance or inhibit the generation and amplitude of tremor through peripheral reflection.

Multiple groups

1. Family history Idiopathic tremor is also called familial tremor. About 60% of patients have family history and are autosomal dominant. Researchers have different reports on family history, ranging from 17.4% to 100%. The reason for this huge difference is that the diagnostic criteria of primary tremor are different. The correct evaluation of the family history of primary tremor depends on the consultation and clinical examination of tremor symptoms.

2. The typical incidence of essential tremor can be seen in children, adolescents and middle-aged and elderly people, and the incidence rate is 0.3%~ 1.7% in the general population, and it increases with age. The incidence rate of people over 40 years old increased to 5.5%, and that of people over 65 years old increased to 10.2%. There is no significant difference in incidence between men and women. It is also reported that the ratio of male to female incidence in Sweden and Finland is 0.5:0.7 1. Essential tremor may be more common in left-handed people.

3. Age of onset Essential tremor can start at any age. There are two views on the peak age of onset. One view is that the age distribution of onset is bimodal, that is, at the age of 20-30 and 50-60. Another view is that idiopathic tremor rarely occurs in teenagers, and the number of patients increases with age, with an average onset age of 37-47 years old.

4. The onset age of tremor has nothing to do with the development of the disease. Most scholars believe that the disease has been progressing slowly and has never been alleviated. The loss of labor force due to tremor began after the onset of 10 ~ 20 years, and the incidence increased with the course of disease and age.