(a) Tonic or tetanic spasm is one in which the muscular contraction is continuous or constant for a measurable length of time. Thus, in some cases of petit mal there is a momentary stiffness or rigidity of the entire voluntary muscular apparatus (respiratory muscles included): the patient sits or stands with staring eyes as if petrified. In tetanus and local tetanoid seizures the muscles of large regions or of a part of a limb may remain contracted for many minutes; in the disease called tetany this condition may endure days and weeks—in hysteria and in some paralyses dependent upon organic disease for years or permanently. Prolonged tonic spasms occurring in chronic diseases are designated as contractures, and the affected parts are said to be tetanoid or spastic. A tonic spasm of long duration may show itself in involuntary muscles, as in the arteries, causing vaso-motor spasm and ischæmia; in the ciliary muscle, causing spasm of accommodation; in the urethra, œsophagus, etc.
A tonic muscular contraction accompanied by intramuscular pain is termed cramp.
Under this general head may also be classed the emotional or dramatic expressive spasms of hysteria and hystero-epilepsy—a condition in which the emotions or ideas occurring in the patient's mind are involuntarily translated externally into attitudes or gestures: e.g. anger, fear, disgust, amorous and religious feelings, etc.
(b) Clonic spasms are those which consist in rapidly intermittent muscular contractions, local or general. These may be rhythmical in time or form, as in paralysis agitans, or wholly irregular, as in chorea. Jerking is a quasi-popular designation of clonic spasms.
Tremor, or trembling, observed in persons during repose in any attitude, consists in small, wholly involuntary muscular contractions of sufficient extent to communicate to the parts a visible to-and-fro movement which is very often rhythmical. In order to distinguish this from any form of inco-ordination it is necessary that the observed movement should occur independently of all volitional effort. Thus in the senile state, in chronic alcoholism, in paralysis agitans, and in dementia paralytica we observe trembling of the facial and lingual muscles, of the extremities, and even of the whole body in some cases. These are usually conditions of permanent or chronic tremor, but the symptom is sometimes observed as a transient phenomenon, as after violent muscular effort, after excesses of various sorts, under the influence of emotions, etc. Occasionally, persons are met with who have trembled from childhood or early years without actual disease of the nervous system. It is clinically useful to divide tremor into varieties, as rhythmical and irregular, fine and coarse, constant and occasional. These terms define themselves sufficiently, so that no further statement is necessary, but we would repeat that it is of much advantage in diagnosis to determine accurately the characteristics of tremor.
2. A much more useful classification of spasms, and to a certain extent a physiological one, is into types according to their distribution in the body, following exactly the classification of paralyses. There are few topics of more utility for the physician to study, in our opinion, than that of monoplegias and monospasms, of hemiplegias and hemispasms in their genesis, mutual relations, and diagnostic significance.
(a) Hemispasm of cerebral origin, tonic or clonic (or both forms associated), may affect the face and limbs on one side of the body, with or without paralysis. As in hemiplegia, the morbid phenomena are greatest in the most distal muscular groups or in those whose innervation is most cortical. Very often hemispasm precedes, immediately or remotely, hemiplegia in the same parts. In other cases the relation is inverse, as when, after a severe hemiplegia, we find the paralyzed muscles in a state of nearly constant tonic contraction (secondary contracture), or when hemi-epilepsy follows a cerebral lesion. In the former case the spasm, clonic or tonic, is designated as pre-paralytic; in the second case, as post-paralytic. These terms are useful, because they are associated with laws of diagnosis and prognosis.
(b) Conjugate deviation of the eyeballs and head is an important symptom of gross cerebral lesions, and may be considered here, although it is probably due to paralysis. Still, the deviation itself always strikes the observer as a spasmodic effect. The symptom consists in a steady turning of the eyes, face, and head toward one or the other side, and may be best described by likening it to the normal act of looking at an object which is on one side or a little back of us. In one form—that due to an irritative lesion of the motor cortex of one hemisphere—the conjugate deviation forms a part of the hemiplegic epileptiform convulsions (mixed tonic and clonic) which are produced: the deviation is away from the lesion. In a second form, where severe hemiplegia is produced by an acute lesion of the motor area and the subjacent fasciculi of one hemisphere, whether the patient be comatose or semi-conscious, the deviation, of paralytic origin, is away from the paralyzed side of the body and toward the injured hemisphere: the patient is said to be looking at his lesion. In a third form, when the lesion is in one side of the base of the brain (more particularly of the pons), the deviation, again paralytic, is away from the lesion, as a rule. In some cases conjugate deviation exists only as a tendency to look to either side. It is always a valuable symptom in severe cerebral affections, more especially the apoplectic state.
(c) Paraplegic spasm is also shown in tonic and clonic forms. Partial tonic spasm of this distribution, with paresis of the legs, causes the gait or attitude known as tetanoid or spastic. The four extremities may be in this state of mixed paresis and contraction, as observed in some very young children whose cerebral motor area is probably undeveloped or ill-developed, or which has been damaged shortly after birth by meningeal hemorrhage.
(d) Monospasm, spasm affecting one side of the face or one extremity, may be of cerebral, spinal, or neural origin. Very often monospasm of clonic form serves to indicate with wonderful precision beginning disease (irritation stage) in limited parts of the cerebrum (in cortical centres and in the connected fasciculi for the face and limbs). Cerebral monospasms are sometimes combined so as to almost constitute hemispasm—i.e. brachio-facial or brachio-crural monospasm. Monospasm may precede or succeed monoplegia.