When tremor first begins it is slight in degree and extent, and occurs generally only on voluntary effort. Later there may be a constant trembling even when the part is at rest. Beginning usually in the hands, it may extend to the head and legs. It is seen in the tongue and facial muscles after the disease has lasted for some time.
In some cases the trembling can be controlled to some extent by a strong effort of will. The tremor from alcohol or opium is most marked when the individual has been without the use of the stimulant for a short time, and the trembling may be temporarily checked by renewing the dose of alcohol or opium as the case may be.
The muscular trembling from plumbism and mercurial poisoning is more violent than the other forms of simple tremor, and often resembles the tremor of paralysis agitans. In toxic tremors there are often secondary paretic symptoms and indications of other disturbances of the brain and nervous system.
In simple tremor there is no loss of muscular power, and the electrical reactions of the affected muscles are not abnormal. The duration of simple tremor is almost always great. Usually it persists throughout life, becoming more general and more intense as the subject of it grows older. The tremor of hysteria is shorter in duration. Occasionally there are seen cases of simple tremor, which are apparently the result of some trivial cause in a nervous person, which last but a short time.
I have seen a case of tremor of the head in a woman of about forty years, in which the trembling ceased entirely after it had lasted several weeks. Hammond3 describes what he calls convulsive tremor. Under this name he includes cases of non-rhythmical tremor or clonic convulsions, which are unaccompanied by loss of consciousness, but are paroxysmal in character. Pritchard in 1822 presented an account of this affection and related two cases; Hammond mentions six cases. The affection is characterized by paroxysms of violent and rapid convulsive movements, which are more or less general and occur many times a day. The seizures last from a few minutes to several hours.
3 Diseases of the Nervous System, p. 696.
The PROGNOSIS in convulsive tremor seems to be favorable.
Tremor may be regarded as a form of clonic spasm. It consists of slight intermittent contractions of individual muscles or groups of muscles. Fibrillar tremor, such as is seen in progressive muscular atrophy, depends on contractions and relaxations of the muscular fibrillæ, and can be seen under the skin, but does not cause any movements of the limb.
There are no pathological data for explaining what portions of the nervous system are the seat of disease in simple tremor. In experiments upon the lower animals it has been found that trembling occurs in muscles which have been separated from the nerve-centres by division of the nerve. So too in man: when there has been a wound or section of a nerve accidentally, there is likely to be tremor in the muscles which it supplies.
The tremor does not begin at once on section of the nerve, but comes on after a few days. As the peripheral end of the nerve undergoes degeneration the tremor increases. It may last months or even years.