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guishable (and to a large extent distinct) from the degeneration of
the nerve-fibres that excites it. It may vary in degree in different
cases, and, even in the secondary degeneration of peripheral nerves,
may assume an independent inflammatory character. Once excited,
the energy of tissue-growth may be in some degree independent of its
cause. Secondary vascular disturbance may attend it, and thus a sub-
inflammatory condition (or even true inflammatory condition) is
probably sometimes developed, which may invade the pia mater, and
through this may spread widely.

The chief causal fact regarding the disease is its common relation
to syphilis. Tabes is generally, although not invariably, a post-
syphilitic disease ; certain elements of the nervous system degenerate
in consequence of the influence on them of previous or present
svphilis. But these elements have a special liability to degenera-
tion, which causes their nutrition to fail from other causes, and
may also constitute their special susceptibility to suffer from the
virus of syphilis. The usual symmetry of tabetic lesions indicates
that the mechanism by which syphilis affects the nervous system is a
blood-state. The manner in which the peripheral nerves suffer in
many cases, brings tabes, in spite of its chronicity, into analogy with
the more acute forms of peripheral neuritis, such as succeed acute
specific diseases at a variable interval. The long interval, moreover,
and the common slowness of the process in tabes when a sequel of
syphilis, are only in proportion to the chronicity of the causal malady,
compared with the acute specific diseases that have neuritic sequelae.
Further, the considerations mentioned in the account of multiple
neuritis, which suggest that its immediate cause, when it is due to
an acute blood disease, is a product of the growth of the organisms
of the primary malady, rather than the organisms themselves, hold
good also in the case of syphilis and tabes. The degenerative changes
in the nervous system differ from the lesions of active syphilis, both
in character and in time, in such a way as to make the assumption



LOCOMOTOR ATAXY. 427

reasonable that they depend upon some product of the growth of the
syphilitic organisms, a product which may possibly be a chemical
substance — a suggestion first made by Strumpell, and widely held
regarding other analogous maladies. Recent research is bringing into
ever greater prominence the important part played by such products
in the generation and course of diseases. In the specific diseases
that have these sequelse, there may be more than one such product of
their organisms, causing more than one kind of consequence. The
differences between such nerve degenerations as those of tabes, and
other late effects of syphilis, is at least not difficult to comprehend
on this hypothesis ; neither is the fact — which has been so great a
difficulty to many —that the treatment which has so speedy an effect on
syphilis itself, is generally without influence on the degenerative pro-
cesses that sometimes follow it.

Tabes is probably a rare sequel, when regarded from the side of
syphilis. But the occurrence of such consequences in some instances,
and not in others, has analogies in the case of almost all the acute
specific diseases that have similar sequelse, and must be taken as
evidence of variations in the precise character of the primary disease.
The virus of the primary malady is doubtless organismal, and such
variations are f amilar to us in the case of other diseases. They some-
times have, and at other times have not, consecutive effects upon the
nervous system, as in the familiar instance of diphtheria. The varia-
tions in the character of the organisms, and in their effects, may be
relatively great, although entirely beyond our present powers of
observation.

These considerations receive a notable emphasis from the occur-
rence of tabes in children who are the subjects of inherited syphilis,
to whom the disease in early life is probably confined. The fact
also shows how potent must be the part played by the agent,
compared with the susceptibility that is, as it were, the causal comple-
ment — a fact seen also in the raritv of cases of tabes in which syphilis
can be absolutely excluded.

The pathological facts already known enable us to understand many
of the symptoms of the disease. There may be an interruption of the
sensory path in one or both of two places, in the peripheral nerves,
and in the posterior root- fibres as they enter the cord, and an
interruption of the fibres in either place will explain the loss of
sensibility which is so frequently present. The pains may reasonably
be ascribed to the molecular changes in the nerve-fibres and their
altered function, either in the periphery or in the cord. The intensity
of a sensation is no measure of that of the process that causes it.
Whether the affection of the sensory cells of the cord* takes part

* In disease of the nerve-roots of the cauda equina there is always ascending*
degeneration of the posterior median columns, but not of the antero-lateral ascend-
ing tract. Hence the root-fibres from which the path is continued by this tract
must end in nerve-cells in the posterior cornua, and the degeneration of this tract



428 SPINAL CORD.

in the production of the anaesthesia and pains, we cannot tell. It
is noteworthy that the affection of the periphei'al nerves must involve
the structures by which the nerve-impulses of sensation are normally
generated by mechanical and other processes. The long persistence
of pains without any increase in the symptoms, shows that they
may be due to the action of structures that are changed, but not
changing. The loss of reflex action from the skin is explained
by the interruption of the sensory path, and an increased irrita-
bility of the sensory nerves, the result of the commencing degene-
rative changes, sufficiently explains both the hyperesthesia and the
increase of reflex action sometimes observed. Whatever theory of the
nature of the so-called " tendon-reflex " action is held, the loss of the
knee-jerk must be explained by an interruption of the sensory path.
On the theory I have advanced, the arrest of impressions from the
afferent muscular nerves abolishes the muscle-reflex action on which
the local irritability depends. Many other facts of disease show that
this irritability is easily lost, and that a very slight change in any
part of the reflex arc, too slight to cause other symptoms, is sufficient
to ai-rest the knee-jerk.* Hence we can understand that this loss
should be constant and early. It is not improbable, moreover, that
these nerves suffer in special degree. The muscles may be insensitive
to pain, e. g. that of electrical stimulation. Pressure and extension,
which in health are painful, sometimes cause no sensation, even when
the skin is sensitive.

The mechanism of the muscular inco-ordination, which is the
obtrusive symptom of the disease, has been the subject of much dis-
cussion. Two fundamental facts, however, limit the problem. First,
the ataxy cannot be primarily clue to the loss of cutaneous sensibility.
Disease of the conducting path in the cord may cause absolute
anaesthesia of the skin without the least ataxy. Although this does
not prove that interruption of the sensory path in the nerves, between
the skin and the reflex centres, may not cause inco-ordination, this
element seems to be excluded by the face that there is no relation
between the ataxy and the loss of feeling in the skin. There may be,
in tabes, much ataxy without any cutaneous anaesthesia, and vice
versa. The second fact is that ataxy may exist in considerable degree
when the lesion is solely one of the peripheral nerves, and the pos-
terior columns of the cord are free from disease.f These two facts,
taken together, seem to show that the ataxy may be produced by one

in tabes is proof of the degeneration of these sensory cells. See the ' Lancet,'
June 19, 1886.

* E.g. its loss after diphtheria when there are no other symptoms.

f Apart from the evidence of this from cases of true tabes, a very instructive case
has been recorded by Dr. Hughes Bennett, in which all the symptoms of tabes were
present in a case of multiple tumours of the posterior nerve-roots (' Clinical Soc.
Transactions,' vol. xviii). Ataxy has also resulted from other processes, such as
injury, that have caused extensive damage to the posterior roots alone.



LOCOMOTOB ATAXY. 429

mechanism, even operating alone, trie disease of the afferent muscle-
nerves. If the loss of the knee-jerk in tabes is to be taken, as I
believe it may, as an indication of the disease of these nerves, the con-
stancy of the loss shows the constancy of the presence of this element,
in some degree. As just stated, a very slight degree of disease may
abolish the knee-jerk; it is probable that a greater degree is needed
to cause inco-ordination, and a still greater change to produce actual
insensibility to pressure or extension.

In unilateral lesions of the spinal cord, as we have already seen (p.
229), there may be loss of the sense of posture, with intact cutaneous
sensibility, on the side of the lesion, and no loss of this sense on the
opposite side, on which cutaneous sensibility is lost. In such a case
marked ataxy has been observed on the side on which the sense of
posture was lost, when motor power returned.* Whatever effect in
causing ataxy is produced by disease of the path of muscular sensi-
bility in the spinal cord must also be produced by interruption of the
path between the muscles and .the cord. The latter- must also arrest
whatever reflex action depends upon these muscle-nerves, f and it is
possible that such reflex action takes some part in the mechanism of
muscular co-ordination.

In this connection it is important to note that the fibres that pass
up by the posterior median columns probably constitute the path from
these nerves. The root-fibres to the columns seem to pass up, as the
path is proved to do, without decussating, and they may be diseased
in intense degree when there is no loss of cutaneous sensibility. J This
tract is affected in almost all cases of tabes in which there is a lesion
in the cord, and in all such cases in which there is ataxy. This
fact suggests that the lesion of the root-fibres is first and chiefly of
those from the muscles. §

The posterior median columns (extensively connected with the cere-
bellum) and the direct cerebellar tract probably conduct to the cere-
bellum the impressions from the sensory muscle-nerves. If so, the
disease of these tracts and nerves must interfere with the co-ordinating

* Gilbert ; see foot-note, p. 229.

f In a case in which the inco-ordination was much greater in the right leg than
in the left, and cutaneous sensibility was equally impaired in the two, a strong trac-
tion on the calf muscles, by forcible passive flexion of the foot, produced a distinct
sensation in the extended muscles of the left leg, and no sensation in those of the
right. In another case, in which the skin was sensitive to the slightest touch, the
patient was unconscious of a vigorous extension of the toes produced by faradic
stimulation of their short extensor.

£ This posterior tract is most diseased on the side opposite to that on which there
is most degeneration of the antero-lateral ascending tract, which probably con-
ducts sensations of pain.

§ The opinion that the ataxy depends on impairment of the muscular sense was
put forward in 1855 by Dr. Russell Reynolds; see p. 398. Dejerine has also asso-
ciated the ataxy with the degeneration of the peripheral sensory muscle-nerves
(' Archives de Phvsiologie,' 3rd series, vol. iii, p. 231).



430 SPINAL CORD.

action of the cerebellum, and cause some part of the loss of function
which results from disease of the cerebellum itself.

There is another mechanism which may co-operate in increasing
ataxy. The vertical fibres of the postero-external column have only
a short course, and some probably connect the posterior grey matter
at adjacent levels. The affection of these fibres seems to be proved by
the fact that the comma-shaped bundle of fibres in the front of the
post.-external column may be specially degenerated. This lesion may
impair the association of the sensory structures, and so cause a want of
harmony in the central mechanism. The theory that the ataxy was
due to this cause was advanced by Todd in 1847. It is not probable
that, if effective, it has more than an intensifying influence, since ataxy
may exist when the posterior columns are throughout unaffected. The
discovery that ataxy may result from alcoholic peripheral neuritis
confirms the view of its origin above stated.

Although cutaneous anaesthesia cannot, alone, produce ataxy, it may
reasonably be assumed to increase that which already exists. Sensa-
tions from the skin furnish important guidance to the motor cerebral
centres, and are probably also concerned in such reflex muscular actions
as that of standing. Similar guidance to the cerebral co-ordinating
centres is also afforded by visual impressions, the loss of which distinctly
augments the defect of co-ordination. The varying characters of the
ataxy in different cases probably depend on the local variations in the
degree of change in the muscle-nerves. The special effect of the
disease of other elements of the cord, related to the posterior roots
(as the posterior vesicular column), has still to be ascertained. The
degeneration of the antero-lateral ascending tract is perhaps con-
nected with loss of sensibility to pain.

It is probable that co-ordination is chiefly an automatic process,
depending partly on muscle-reflex actions, and on the connection of
neighbouring sensory structures in the spinal cord, but chiefly on the
function of the cerebellum, determined by the connection of the
muscles with it, and that the interruption of this connection is the chief
element in the inco-ordination of locomotor ataxy. It is probable also
that the automatic processes are in part under cerebral control, guided
by sensory impressions which do enter the sphere of consciousness, and
that the derangement of this control will intensify inco-ordination,
though incapable of producing it. We do not at present know to what
extent, in any given case, the symptoms are due to the cord disease or
to the peripheral nerve lesions. Apparently pains, ataxy, and anaes-
thesia may be due to either. The question can only be decided by the
comparison of symptoms and pathological changes in a large number
of cases. That anesthesia may be due to the peripheral changes
is proved by the observed correspondence of the two in distribution
(Dejerine).

The trophic changes in the skin, bones, and joints are probably due
to the process of degeneration in the peripheral nerves. The degenera-



LOCOMOTOR ATAXY. 431

tion has been found in all cases of the kind in which it has been looked
for, and found also in the nerves of diseased joints. The pathology of
the muscular wasting has been already mentioned.

The pains in the region of the fifth nerve are explained by the lesions
in its root, especially in its ascending root, which, coming up from the
medulla, is homologous with the posterior spinal roots. This nerve,
indeed, as Pierret has pointed out, represents the sensory roots of
almost all the motor cranial nerves. The degeneration of the optic
nerve is fairly comparable with that of the peripheral spinal nerves.
Considering the special character of the optic nerve, the absence of
degeneration of the retina does not seem to desti-oy the analogy between
the two. Regarding the pathology of the visceral crises we know but
little. The changes observed by Pierret in the neighbourhood of the
centre for the pneumogastric may be, as Buzzard has suggested, an
indication of the cause of the disturbances that occur within the
range of this nerve, especially of the gastric and laryngeal crises.

The transient motor symptoms in the limbs, and in the eyeball
muscles, are apparently of functional origin. They must be distin-
guished from the lasting palsies, which are probably due to degene-
rative processes in the nerves or nuclei ; the loss of function of the
internal ocular muscles, being persistent, must be ascribed to degene-
ration of the related centres. But even the light-reflex may return
after it has been absent for years, and its loss must therefore depend,
at least sometimes, on molecular changes capable of recovery. It is
indeed important to remember that tabes is a disease which begins as
a derangement of molecular nutrition, which is probably only to be
discerned when relatively great in its degree. If we also remember
that this derangement is the result of some toxic material or virus
circulating in the blood, we can understand better the leading facts of
the disease, and especially the variations in its course, its degree, and
the precise character of the symptoms.

Diagnosis. — The diagnosis of tabes rests on the combination of
symptoms already described. In the early stage, the loss of the knee-
jerk, together with pains, or unsteadiness on standing with the feet
together and the eyes closed, justifies a diagnosis of the commencing
affection, provided we can exclude toxic peripheral neuritis (especially
that due to alcohol), diabetes, diphtheritic palsy, and also a lesion of
the anterior cornua or nerve-roots by the absence of wasting of the
muscles and change in their irritability. The diagnostic value of the
loss of the knee-jerk can hardly be overrated. It is probably never
absent in health. If there is doubt as to its loss, the precautions
recommended on p. 15 should be adopted. When it is lost, and reflex
action is in excess, a true reflex movement may sometimes simulate
the jerk ; the distinction is that the tap sometimes causes a movement
and sometimes does not; that an interval, brief but appreciable,
elapses before the movement occurs ; that a similar movement is
caused by a prick on the skin, and that the delayed contraction some-



432 SPINAL CORD.

times occurs in the other leg, or in the adductors of "both legs.* In
cases in which the knee-jerk is present, the diagnosis of tabes is only
justified by distinct and eharactei'istic inco-ordination. In the few
cases of this kind that have come under my own observation, the knee-
jerk has been either unequal on the two sides, or has been lost on one.
Such abnormality is probably the rule in these cases, and the diagnosis
is thus facilitated. In a case with lightning pains, but neither inco-
ordination nor loss of knee-jerk, a suspicion of tabes would be justified
by the presence of some other symptom, such as retention or incon-
tinence of urine, loss of sexual power, or loss of the iris-reflex. But,
as we have seen, it is probable that cases occur in which these
pains exist alone, — a condition that may be termed "tabetic neu-
ralgia."

The loss of the iris-reflex is of great diagnostic importance. It
shows that a degenerative process is at work in the nervous
system, and it suggests, therefore, that other symptoms are also due
to degeneration. But since the iris-reflex is not always lost in tabes,
the negative significance of a normal reflex is far less than is the posi-
tive significance of its loss. The practical value of this symptom can
hardly be overrated. It puts the observer, so to speak, on the track
of nerve degeneration. Its loss is, moreover, so often due to preceding
syphilis, that it should always suggest this antecedent.

There are certain diseases with which tabes is especially liable to
be confounded. One of these is multiple alcoholic neuritis. The
ordinary form of this disease is readily distinguished by the symme-
trical paralysis which is its chief manifestation. But the variety
which closely resembles locomotor ataxy is the " alcoholic pseudo-
tabes " (p. 125), and in this the diagnosis may be very difficult. This
is not surprising, because it resembles tabes pathologically ; the lesion
is a " parenchymatous neuritis," a subacute degeneration, beginning
in the nerve-fibres, and similar to the peripheral form of tabes. It
often affects, however, in some degree, the motor as well as the sen-
sory nerves, and there is then some weakness in the distal portions of
the limbs. An altered electrical reaction may be found in the muscles
(never in the weakness sometimes met with in early tabes), and there
is generally marked muscular tenderness, scarcely ever present in
tabes. The pains have not the "lightning" character, and the
sphincters escape. The pupils act normally, but this is not an
absolute distinction, since they may be unaffected in tabes. A history
of alcoholism may help the diagnosis, and so may improvement when
alcohol is withdrawn. By attention to all these points, a diagnosis
can generally be made without much difficulty.

When the symptoms and lesion of tabes are combined with those
of general paralysis of the insane, it may be doubtful in which cate-

* It is impossible to exaggerate the difficulty presented by some patients in ascer-
taining whether the knee-jerk is or is not lost, and the care needed, and repeated
observations that are desirable, in doubtful cases.






LOCOMOTOR ATAXY. 433

gory a case should be placed. The question is rather one of the pre-
ponderance of the symptoms of one or the other malady than of
absolute distinction between them. In most eases, however, in which
this combination exists, the symptoms of general paralysis become
more pronounced as time goes on, and the spinal symptoms, which at
first were the most conspicuous, pass into the background.

All common forms of paraplegia are distinguished by the early
loss of power, and by the persistence of the knee-jerk, often
emphasized by its excess and by the occurrence of a clonus in the
rectus or the calf muscles. If weakness supervenes in tabes, it is
usually late in the courc3 of the disease, and the other symptoms
have been and are well marked. If the knee-jerk has been once
lost in this disease, it is not reproduced by secondary lesions of
the cord which ordinarily increase the knee-jerk. The same distinc-
tions usually suffice for the diagnosis from the combined form of
paralysis and inco-ordination that I have termed " ataxic paraplegia."
In this the knee-jerk is excessive, and there is foot-clonus, while pains
and aiuesthesia are absent ; spasm supersedes ataxy. In other forms
of combined disease of the cord the diagnosis depends chiefly on the
recognition of union.

Acute lesions of the cord, probably situated in the postero-external
column, may produce inco-ordination and piain, but the suddenness of
the onset, the limitation of the symptoms, and their tendency to sub-
side, usually suffice for the distinction. Symptoms from this cause
are far more common in the arms than in the legs. Ataxy in one limb
may also be produced by a tumour growing in the posterior column,
but other symptoms indicate the invasion of adjacent structures, as
was conspicuous in the case figured in the chapter on tumours of the
cord. All these cases present the characteristics of a focal lesion with
random consequences, rather than of a system disease with limitation
to a special function.

In diphtheritic paralysis occurring long after the sore throat, or in
which the nature of this was not recognised, the loss of the knee-jerk
may cause tabes to be suspected ; but the nature of the case is almost
always rendered clear by the paralysis of accommodation and of the
palate which precedes the ataxy, and should be suggested by the
absence of pains and the presence of weakness. If true tabes follows
diphtheria, the sequence is too rare to be of practical importance.

When the dorsal region of the cord is chiefly affected, the severity
of the pains in the trunk may lead to a suspicion of disease of the
vertebral bones, but in the latter the pain is local and fixed, and this,
with the characteristic increase of pain when the patient moves, should
prevent error. It is still more frequent to mistake such cases for
neuralgia of the intercostal nerves, but even if there are no pains in
the legs to suggest tabes, the knee-jerk and the light-reflex of the iris
are lost in tabes. Experience shows that the most frequent errors in
diagnosis are due to a mistake as to the nature of the pains, which

vol. i. 28



434 SPINAL COM).

are mistaken for rheumatism, especially when influenced by weather,
or for sciatica when referred to the region of the sciatic nerve, or for



Online LibraryW. R. (William Richard) GowersA manual of diseases of the nervous system (Volume v.1) → online text (page 52 of 79)