Tremor is a prominent symptom of many diseases of the nervous system, and is met with as an effect of certain poisons which have been taken into the system; so it should not be considered as a disease in itself. It may, however, occur without being associated with any other abnormal condition which can be discovered. It is then called tremor simplex or tremor essentialis. The tremor of old age (tremor senilis) comes under this head.
Tremor is sometimes hereditary, and may exist from early life. I have a patient in whom there is a trembling of the hands which has lasted since childhood. This lady's mother and grandmother both had the same form of tremor, and one of her own daughters also has it. In this case the trembling is most marked when voluntary movements are attempted, but it does not materially interfere with writing, sewing, or any other act she wishes to accomplish. There is slight tremor when the hands are at rest.
Tremor simplex is seen in hysteria. In this disease it affects the hands and the facial muscles as well. It is not uncommon in these cases to find the tongue tremble excessively when protruded.
Tremor from chronic poisoning is usually from the absorption of lead, mercury, or some of the narcotic drugs or alcohol. Lead tremor is to be looked for among persons who are exposed to the action of lead, such as painters, printers, or manufacturers of white lead.1 Such persons generally have had some other symptom of lead-poisoning, such as colic or paralysis. The tremor, however, may be the only symptom of saturnine poisoning. Mercurial tremor is not so often seen. It occurs in looking-glass makers or those who work in quicksilver, and may also be a result of the medicinal administration of mercury. The tremor from the excessive use of alcohol or opium is familiar to all. Tobacco, if used immoderately, also causes trembling in the hands. Tea or coffee may have the same effect. There are other drugs which, when taken for a length of time, are liable to cause tremor. Quinine is one of these.
1 Lead in hair dyes or in cosmetic powders often gives rise to plumbism by its absorption by the skin.
Exhausting diseases, like the fevers, or any conditions which enfeeble the system, cause tremor which occurs in voluntary effect. I saw a lady some years ago who was greatly weakened by a malignant growth. She was extremely anxious to sign her name to a legal paper, but, although the hand was perfectly quiet when at rest, when she attempted to write the first letter such intense tremor came on that it was impossible for her to make any mark which was legible.
Tremor follows violent bodily exertion or mental excitement. The action of cold or the chill of intermittent fever is accompanied with an extreme degree of trembling, which we all know. Tremor is also a result of neuritis, but in this case it is associated with other symptoms.
SYMPTOMS.—Tremor is met with as a fine or a coarse trembling. We may also find a fibrillar tremor, such as exists in progressive muscular atrophy. Tremor is divided by some (Van Swieten, Charcot, and others) into two classes: the first is where the tremor occurs while the part is at rest; the second is where it comes on during volitional muscular movements. The former has been termed by Van Swieten tremor coactus, because he believed that it arose from an irritation which affected the nervous centres in an intermittent way. The latter he conceived to depend upon a defect of stimulus, the result of an insufficient amount of nervous fluid, which causes contraction of the muscles under the influence of the will. This he called tremor a debilitate.2
2 Charcot, Lectures on Diseases of the Nervous System.
In paralysis agitans we have an example of tremor coactus, and in disseminated sclerosis, where the tremor occurs only as muscular effect, it belongs to the variety of tremor a debilitate. Those divisions, however, are of but little importance.