SYMPTOMS OF DISEASE OF THE SPINAL CORD: INDICATIONS OF THE SEAT OF THE LESION: ANATOMICAL DIAGNOSIS.

The symptoms of disease of the spinal cord consist in derangement of its various functions; the loss of some, the exaltation and perversion of others. We have already considered these functions, and the parts of the cord by which they are subserved. We may now briefly consider the general character of their derangement, and its significance in regard to the position of the disease. The combination of symptoms indicates the seat of the lesion; we infer its nature from their mode of development, and other considerations, which will be subsequently discussed. It is always important to keep these two elements of the diagnosis distinct in the mind.

A common feature of the symptoms of disease of the spinal cord is their bilateral character. This depends on two causes, of which, however, only the first is peculiar to the cord and can be regarded as the special cause of this feature of its diseases. The structures in each half of the spinal cord are in such close proximity, that any random process, such as hæmorrhage or inflammation or pressure, readily affects both halves-can, indeed, hardly fail to do so in some degree, and usually to such an extent as to cause the bilateral character of the symptoms to be obtrusive. Secondly, morbid processes that commence in the nerve-elements and affect them according to their function ("system diseases ") usually involve the corresponding structures of the two sides, and the spinal cord contains many structures that are liable to such processes. Hence a large proportion of the diseases of the spinal cord involve both sides and cause symptoms that have a corresponding range. The leading fact that results from this is that the characteristic type of palsy is "paraplegia." The word means literally paralysis of the parts beneath or beyond a certain locality, and involves the distinction of a motionless part of the frame, which no doubt arose from the variable extent of this, in comparison with the uniformity of the region affected in "hemiplegia." But the second condition causing the bilateral character of the symptoms is shared equally with those outlying parts of the spinal cord-the peripheral nerves; and as this condition obviously determines a stricter symmetry than does the first, it follows that this character is not, alone, of much significance, and is indeed least significant when most complete. In the affections that are strictly symmetrical, therefore, other features must also be taken into account.

Another character of spinal symptoms, not shared by those of the nerves, consists in their variation in vertical extent according to the position or extent of the lesion. But we must distinguish two classes of symptoms within the region in which they exist. (1) Those which depend on the interruption of the conducting path to or from the brain, and involve the whole region below the disease. (2) Those which

depend on damage to the central structures in the cord and nerve-roots, which are present only at the level of that damage, i. e. in the parts functionally related to that part of the cord. The two sets of symptoms may be distinguished as "conducting" and "central;" but in many diseases those at the level of the lesion are chiefly due to the irritation of the nerve-roots, and these are most usefully designated "root symptoms."

Disease of the cord does not always cause bilateral symptoms. A little consideration will show that this must be so. A random process, of small extent, may damage one side only. It may affect one or several structures on one side or all of them. Nevertheless it

is very rare for such a process to spare the other side altogether, and practically no lesion affects all parts of one side without damaging, in some degree, the other side, at any rate for a time. In very rare forms of traumatic lesion, however, the damage to the other side is almost imperceptible. Again, "system diseases," in quite exceptional cases and for unknown reasons, are limited to one side; much more frequently they may affect one side earlier and more than the other. Such unilateral symptoms have been awkwardly termed "hemiparaplegia."

MOTOR SYMPTOMS.-Loss of motor power results from interference with the motor path in any part of its intra-spinal course,―pyramidal tracts, anterior grey matter, anterior nerve-roots. We have seen that the path may be divided into two segments, upper and lower (see p. 176). The spinal cord contains a considerable portion of the nervefibres of the upper segment, and their lower termination in the grey matter, but only the commencement of the lower segment, the motor ganglion-cells, and root-fibres proceeding from them. The chief part of the lower segment is outside the spine, in the nerve-trunks. So far as the loss of power is concerned the effect is the same, in whatever part of the motor path the interruption is situated; but the other symptoms that accompany the loss of power differ very much according as the interruption is in the upper or lower segment. The lower segment influences muscular nutrition, and forms part of the path of reflex action. Hence, as we shall presently see, the muscles waste, and reflex action is lost, when this is diseased; but when the upper segment is damaged there is no muscular wasting, and reflex action, instead of being lost, is commonly increased. The symptoms produced by disease of either segment are essentially the same, whatever part of the segment is diseased, whether the cell at the upper extremity, the fibre, or the ramification at the lower extremity of the fibre. If, for instance, the intra-muscular nerve-endings are paralysed by curara the symptoms produced are the same as if the fibres in the nerve-trunks are divided or these cells in the cord are destroyed. Disease of the termination of the upper segment in the grey matter of the cord must, of necessity, produce the same effect as disease of the pyramidal fibre itself, or the cell in the cerebral cortex from which the fibre springs.

We shall afterwards see that this consideration has very important applications.

If a fibre of either segment is seriously damaged, it degenerates below the division, since its nutrition depends on the influence of the cell from which it has sprung. If damaged only by pressure, however complete may be the evidence of degeneration, regeneration is possible, even after one or two years. It is possible that such regeneration also occurs when the damage is by inflammation. The nutritional stability of the fibre, or rather of its essential element, the axis-cylinder, becomes less, and more easily deranged, the greater the distance from the parent cell, and it is least in the terminal ramification of each segment. This is probably the reason why curara acts chiefly on the intra-muscular nerves, and it explains the influence of many poisons on the peripheral nerve-endings, and the facts of nerve-degeneration in tabes and "multiple neuritis," &c. The law is probably also true of the upper segment; and if so, many facts of pathology become clearer to us, as will be seen in the chapter on "spastic paraplegia." It may thus be taken as a general law of the utmost importance that the vitality of a nerve-fibre and its power of resisting morbid influences are less the greater the distance from the cell from which it springs and of which it is really part.

A lesion of the pyramidal tract causes loss of power in all parts below the level of the disease—that is to say, of all parts the fibres for which are interrupted. A lesion of the grey matter, or of the anterior roots, causes paralysis only of those parts which are functionally on the level of the lesion. The two mechanisms often coincide. A transverse lesion in the cervical enlargement, for instance, may cause paralysis of the arms from the damage to the grey matter and nerve-roots, and paralysis of the legs from damage to the pyramidal fibres. The disease involves, primarily in the former case, the commencement of the second segment of the motor path for the arms; in the latter, the middle of the upper segment. The associations of the paralysis differ accordingly. The parts affected by a lesion at any level will be readily ascertained by an examination of the table of functions on p. 210.

It is important to note that the affection of motor power is often incomplete. It may then involve one set of muscles more than another. The flexors or the extensors may be chiefly paralysed. In disease of the dorsal cord, it is very common for the flexor muscles of the hip and knee to suffer more than the extensors. Why this should be we do not know, but the fact is important, because considerable weakness of the flexors of the knee is readily overlooked. In examining motor power, each set of muscles should be separately tested. Motor over-action; Spasm is frequent in disease of the spinal cord and its membranes. It may present the form of tonic spasm, which when persistent is termed rigidity, or of clonic spasm, which is usually transient and paroxysmal. Tonic spasm, persistent, and involving

only a certain group of muscles, causes distortion of the parts to which they are attached, and is often termed contracture. Tonic spasm, paroxysmal or persistent, is far more frequent than clonic spasm, which occurs chiefly in association with tonic spasm as the muscular clonus described at p. 222, or as a consequence of certain functional derangements. Tonic spasm may be the result of direct irritation of the motor structures, or may depend on over-action of the reflex centres, due, not to irritation, but to deficient control. Either form may be acute or chronic. The acute irritation which causes spasm is generally inflammation of the membranes, rarely an acute lesion of the substance of the cord. The chronic irritation is chiefly due to compression of the motor fibres-either of the pyramidal tracts, when there may be persistent unvarying spasm in the parts below the disease, related to the fibres irritated,-or of the nerveroots, when similar spasm is produced in the parts at the level of the lesion. The spasm that depends on reflex action is seen chiefly in the legs and trunk, but especially in the former. It may preponderate in either the flexors or extensors, so that the legs, when rigid, may be drawn up or straight out. The flexor spasm seems to be due to an over-action of the centres for cutaneous reflex action, the extensor spasm chiefly to that of the centres for muscle-reflex action, although it may also be excited indirectly by a cutaneous impression. This form will be considered in connection with the reflex over-action.

Muscular Contraction.-The actual shortening of muscles, by which they cannot be passively extended to their normal length, is due to tissue changes fixing the active persistent tonic spasm or contracture just mentioned. The rapidity with which it occurs depends on the uniformity of the spasm, and we may distinguish three modes in which it arises, which differ in the time required and degree attained. (1) When one set of muscles is paralysed, their opponents, never being extended, quickly become fixed in the contracted condition which they assume in virtue of their power of adaptation to posture. Thus in palsy of the flexors of the ankle, the calf muscles quickly become contracted, so that the foot cannot be flexed on the leg even up to a right angle. The same thing happens by a similar mechanism, when one posture is unceasingly maintained and one set of muscles are never extended, e. g. persistent flexion of the knee leads quickly to structural shortening of the hamstring muscles. (2) Where there is unchanging active contracture from chronic irritation of the motor fibres by a growth, or permanent reflex contracture, as when reflex flexor spasm keeps the hip and knee permanently flexed, similar structural changes occur, so that passive elongation soon becomes impossible. (3) In paroxysmal tonic spasm of intense degree, if one set of muscles is stronger than their opponents, their action may so preponderate as to lead to a greater active contracture than their opponents present, and permanent shortening may occur; although it does so slowly and to a slighter degree than in the other forms, because

the muscular action is more or less paroxysmal and varying, and the muscles are at times extended by their opponents. Thus in paroxysmal extensor spasm in the legs, no shortening occurs in the muscles moving the knee, because they are equally balanced, but the calf muscles, being stronger than the flexors of the ankle, contract the more, and extend this joint, whenever a paroxysm of spasm comes on, and, after a time, may undergo slight structural shortening, so that the foot cannot be flexed on the leg beyond a right angle.

It is of great importance to distinguish the shortening of muscles due to tissue changes in them, from the active contracture that may closely simulate it. In the latter, gentle extension, kept up for a few minutes, restores the muscle to its normal length. The importance of the distinction is due to the fact that the structural shortening can be removed by tenotomy or forced extension, while these measures are useless in the case of active contracture, which would subsequently reassert itself.

Inco-ordination of movement, although motor, depends usually on disease of afferent fibres. Its characters have been already described in outline (p. 7).

It occurs in three forms, of which the third differs entirely from the others in aspect and nature, and alone is a true motor symptom. The two chief forms are the following :-(1) Simple disorder of voluntary muscular contractions, which, when considerable, amounts to a wild irregularity of movement, and when slight is only manifested by slight irregularity when the guidance of vision is withdrawn-as in the inability to maintain the muscular contractions in the perfect uniformity needed for equilibrium when the base of support is rendered small by the juxtaposition of the feet. The delicacy of the test is increased by the removal of the firm base afforded by the boot, and by closure of the eyes. The increase in unsteadiness when the eyes are closed is sometimes termed "Romberg's symptom." This condition results from interruption of the afferent path from the muscles to the spinal cord, including the fibres that ascend the cord and those that subserve the muscle-reflex process at the level of entrance. The effect of the loss of the latter is a cessation of the chief part of spinal co-ordination, which, as we have seen, depends on those processes, co-operating with the voluntary impulse. Hence it is associated with loss of the knee-jerk. The loss of other forms of reflex action does not seem capable of causing inco-ordination. In complete interruption of the root-fibres from the muscles the mechanism of the next form is necessarily conjoined. (2) Inco-ordination resembling the slighter degrees of that just described, and consisting especially in such a defect of equilibrium as results from disease of the middle lobe of the cerebellum, is produced by disease of the posterior median columns above the lumbar enlargement, or, if it extends into the latter, leaving the root-zones free so as not to impair muscle-reflex action. This is apparently produced by interruption of the path by