Locomotor ataxia (tabes dorsalis), an introduction to the study and treatment of nervous diseases, for students and practitioners

Front matter

THE LIBRARY

OF

THE UNIVERSITY

Preface

As the brilliant researches of Sherrington upon reflex function, of Head, Holmes, Sherren and their co-workers upon sensory function, and of Langley, Gaskell, Biedl, and Gley upon vegetative function, have revolutionized our knowledge of nervous phenomena, it is now essential to restudy every nervous disease, to interpret its symptoms with the aid of this new knowledge, and to organize its treatment according to the new interpretation.

This book correlates our present anatomical, pathological, physiological, and psychological knowledge with reference to locomotor ataxia. The correlation has been planned solely with a view to treatment. Matters having no direct bearing on treatment do not, therefore, receive the attention which they usually enjoy in text books on nervous diseases.

As a student I suffered, in common with every other student, from inability to understand, through my training in anatomy and physiology, the clinical evidence of nervous diseases. So nervous diseases then interested me mainly as a compulsory exercise in memory, decreed by captious examiners. The student's lack of power to apply knowledge is recognized by all teachers. It is inherent to the phase of being taught. A mind attuned to acquire facts in bulk cannot simultaneously fix and correlate them.

After his preliminary training in the fundamental sciences of anatomy, physiology, pathology and psychology, the student should be taught, from a concrete example, how normal structure varies in nervous disease; how, from this anatomical variation, physiological and psychological consequences follow which make the symptoms inevitable and the treatment effective. With this training he will intelligently approach any nervous diseases he may subsequently encounter; he will become a thinking instead of an automatic physician, and nervous diseases will so interest him that much of their difficulty will disappear.

The student's royal road to the understanding of nervous diseases lies through tabes. In tabes there are demonstrable the

603496 viii PREFACE

exciting cause — the spirochete, the lesions — the structural effect of that cause, and the physiological and psychological consequences of these lesions. Reflex integration and its disturbance, interruption of sensory and of motor paths, vegetative disorders, and the interaction of the psyche with the sensory, motor, and vegetative nervous systems, all can be presented connectedly and concretely to students through the study of tabes.

Indeed, there are few facts in neurology which cannot be demonstrated in tabes; and there are few nervous diseases so amenable to treatment as it is. The physiological and psychological basis of the treatment is obvious ; the results seem often miraculous. Students trained in neurology through the teaching of tabes respect the science, value it, and practice it.

Hence I explain the physiology and the psychology of function in detail which would be unnecessary, were I writing solely for my present and not also for my future colleagues. I especially emphasize the role of the vegetative nervous system, partly because of our former neglect of it, but mainly because of the superlative importance it has not only in producing the symptoms but likewise in permitting the disease.

There is a psychological as well as a physiological element in all symptoms, in all disabilities. Psychological treatment is, therefore, as essential as physiological treatment. In many medical cases psychological treatment is the only treatment necessary, and in some of the others it is the only treatment possible. By those who ordain the medical curriculum, physicians are, presumed to be endowed with the art of psychological treatment. We might as well be presumed to inherit the healing touch. Psychotherapy must be taught in the schools or medicine cease to be a legally restricted profession.

Upon the reciprocal relations of the mental state and the tabetic symptoms, and upon the interdependence of the symptoms, rests the basis of psychological treatment. "Without knowledge of these relations, effective treatment is impossible.

Treatment based on these relations does not lead to radical cure, to the removal of lesions. But we can rarely remove nervous lesions; and often it is mainly the mental reaction to lesions which determines the pain or ease, the misery or comfort of patients. Psychic treatment counteracts unfavorable mental reactions and thus minimizes the influence of lesions. It further educates the patient to control residual symptoms,

PREFACE ix

to protect himself against their aggravation; and when such aggravation does occur it enables him quickly to alleviate it.

I systematize the application of this knowledge, for the principles upon which the tabetic's treatment is founded are not restricted in their usefulness to tabes. They are obviously applicable to the treatment of all conditions in which the mental state aggravates symptoms, or in which symptoms threaten the integrity of the mental state.

The method of treating ataxia wrhich I have advocated since 1912, and which I now fully describe for the first time, is based on the thesis that perfect thinking is essential to perfect moving ; and perfect moving is the outward sign of perfect thinking. Training in perfect thinking is, therefore, training in perfect moving ; and training in perfect moving is training' in perfect thinking. The details of the training and the measures needed to ensure optimal conditions for it, I have carefully outlined.

In this material and impious age the Jordan flows unheeded and the waters of Bethesda rise unwatched. Healing words replace healing waters. Religion and health are unhappily confounded by those who foster the Emanuel movement and by the earnest members of that faith which is disguised as science and called Christian. Where remorse is morbid, or suffering is due to ignorance of Divine love, ecclesiastical ministration is proper and pertinent ; beyond these limitations, it is ultimately destructive to the faith which excuses it and to the health which it seeks. Medical inadequacy led to these -movements; the measure of their success is the measure of our failure.

The cause of our failure is neglect of the study of the reciprocal relations of symptoms and mental states. The unauthorized, ignorant of the source of symptoms, but efficient in molding the mental state of the faithful, bring relief to those whom misguided medical effort has failed to ease. It is a matter of congratulation for all when suffering is relieved by any one. A sufferer has an inalienable right to seek relief at any source. We cannot continue to preempt the power to heal when others succeed where we fail, nor can the community allow suffering to be subject to the ignorant.

To his science no less than to ,his conscience the physician owes the duty of giving mental ease to his patient. That ease must be given, not through stupefying with mystic incantations and irrational suggestions, but by rousing the patient to the nax PKEFACE

ture of his danger and by teaching him to organize his own defense.

Only through mental training will the sick unfailingly receive aid in defending themselves against the tyranny of symptoms. Defense based upon self-control over mental processes is more potent and permanent than that afforded by the degrading and treacherous support of suggestion, and more worthy and secure than that which is founded upon ignorant mysticism.

The source of each borrowed illustration is indicated in its caption. I am grateful to the several authors whose illustrations I have used.

I am indebted to Doctor Abrahamson, Professor of Clinical Neurology at Bellevue Medical School, Neurologist to the Central and Neurological, Montefiore, and Mount Sinai Hospitals, New York City. His great experience and knowledge were always at my service and were of invaluable assistance in many difficulties. Doctors Grossman and Wolf have earnestly worked with me and the former has kindly placed some excellent photographs at my disposal.

Years ago, when I was the Crichton Research Fellow, Doctor C. C. Easterbrook, the distinguished director of the Crichton Royal Institution, Dumfries, Scotland, stimulated me with his great enthusiasm for applied psychology. The length of my latent period is due mainly to the war; to that cause also, I hope, he, kindliest of critics, will attribute what is lacking in the following pages.

. Doctor H. R. Storer of Newport, Rhode Island, kindly corrected the proofs.

WILLIAM J. M. A. MALONEY 156 East 79th Street

New York City

Contents

I.— THE SPIROCHETE AND TABES. THE SITE OF THE STRUCTURAL CHANGES PRODUCED BY THE SPIROCHETE IN THE CENTRAL NERVOUS SYSTEM 1

Discovery of tabes. Controversy concerning its cause. Relation of tabes to syphilis. The Spirochaeta pallida, the exciting organism of tabes. Strains of spirochete. Spirochetes that persist in the human host and attack tissues usually immune. The three varieties of the persisting spirochete. The attacking force of the persisting spirochete. Invasion by the persisting spirochete of vascular, glandular and nervous tissues. Causes which determine that the major attack shall fall upon the central nervous system. The spirochete's invasion not restricted to any one area in the central nervous system. Factors which determine the initial site, the extent and the direction of the spirochete invasion in the central nervous system.

IL— RESULTS OF THE SYPHILITIC LESIONS: DIS- TURBANCE OF THE REFLEX MOTOR FUNCTION 18

Chapter I

THE SPIROCHETE AND TABES. THE SITE OF THE STRUC- TURAL CHANGES PRODUCED BY THE SPIROCHETE IN THE CENTRAL NERVOUS SYSTEM

Discovery of tabes. Controversy concerning its cause. Relation of tabes to syphilis. The Spirochaeta pallida, the exciting organism of tabes. Strains of spirochete. Spirochetes that persist in the human host and attack tissues usually immune. The three varieties of the persisting spirochete. The attacking force of the persisting spirochete. Invasion by the pei'sisting spirochete of vascular, glandular and nervous tissues. Causes which determine that the major attack shall fall upon the central nervous system. The spirochete's invasion not restricted to any one area in the central nervous system. Factors which determine the initial site, the extent and the direction of the spirochete invasion in the central nervous system.

AFTER hazy recognition by Todd (1847) in England and by Romberg in Germany (1841-51), tabes was discovered by Duchenne of Boulogne and its symptoms definitely separated from those of other diseases in his classical work on "Ataxie locomotrice progressive" (1857-58).

Since Duchenne 's day, Charcot, Dejerine, Egger, Fournier, Pierre Marie, Marinesco, Nageotte and Raymond in France; Erb, Forster, Friedrich, Goldscheider, Leyden, Moebius, Oppenheim, Striimpell and Westphal in Germany ; Argyll-Robertson, Byrom Bramwell, Graham- Brown, Buzzard, Ferrier, Gowers, Hughlings Jackson

and James Taylor in Britain; Jelliffe, Mills, Noguchi,

l

Patrick, Spiller and Spitzka in America; Krafft-Ebbing and Schaffer in Austria; and Frenkel in Switzerland, have by their genius and labor conferred upon us most of our present knowledge of tabes.

The cause of tabes has been the subject of speculation and controversy almost from the discovery of the disease. Erb and Moebius stoutly upheld the syphilitic origin of tabes. Fournier believed not only that syphilis is the cause of tabes but also that he could gauge from the nature of the banal lesions of syphilis the probability of the later occurrence of tabes. Hitzig taught that tabes is due to a toxin liberated somewhere as the result of accident. Others incriminated shock, overwork, heredity and diverse causes.

With Schaudinn's discovery of the Spirochaeta pallida, the protozoon that causes syphilis, renewed interest in this controversy arose. Failure to find the spirochete in the tabetic lesion and lack of success of drug treatment directed against the spirochete in tabes led most clinicians to agree that tabes was due to a toxin. This toxin was believed by the majority to be a by-product of the spirochete 's activity; by Brissaud to be liberated from the lymphocytes. Tabes free from all taint of syphilis was still thought to occur, and tabes not causally but accidentally associated with syphilis was supposed to be possible.

Wassermann proved that a substance detectable in the blood and in the cerebrospinal fluid may result from infection by the Spirochaeta pallida. Its presence practically signifies syphilis but its absence does not preclude syphilis. Mclntosh and Fildes found the "Wassermann substance in the cerebrospinal fluid of over ninety per cent, and Hauptmann and Nonne in one hundred per cent, of cases of tabes. Spirochete infection is, therefore, an invariable accompaniment of tabes. There is no tabes without syphilis.

Vedder ascertained by blood examination that seven-

FIG. 1. — Spirochetes in the brain of a general paralytic. (Noguchi.)

teen per cent of the recruits of the United States Army are syphilitic. As syphilis occurs only in seventeen per cent of the non-tabetic and in one hundred per cent of the tabetic, syphilis has a causal relation to tabes. In tabes a degeneration .of the nerve processes and a proliferation of the cells of the blood vessels and of the stroma occur. These lesions are of a nature compatible with syphilitic origin.

Pathologists now recognize, at the starting point of

I

FIG. 2. — The Spirochaeta pallida in the brain of a general paralytic. X 1 100.

(Noguchi.)

every tabetic change, an exudative focus. Exudates are evidence of inflammatory, not of toxic, action.

In the tabetic exudate Noguchi and others found the spirochete viable and culturable.

No organism other than the spirochete has been found in the inflammatory foci of tabes.

As syphilis is invariably present in tabes, as syphilis has a causal relation to tabes, as the lesions of tabes are such as could be produced by the spirochete, as the spirochete has been detected in the tabetic lesions, and as it is the only known organism which has this constant association with tabes, the Spirochaeta pallida must be the exciting organism of tabes.

The Wassermann substance can be detected in the blood a few weeks after the primary inoculation : according to Wile and Stokes, Nichols and others, the majority of the cases of syphilis in the secondary stage and many in the primary stage show evidence of the infection in the cerebrospinal fluid also. The local inoculation with syphilis, therefore, early becomes a general infection.

When the infection is general the tissues are equally accessible. The tissue first attacked must, therefore, be that which affords the most favorable soil for the spirochete 's growth. The skin and the mucous membranes are the contact surfaces of human beings. From the skin and mucous membrane lesions of one host originate lesions of the skin and mucous membranes of another host. The most frequent and often the only sign of the family taint in the wife and child of a tabetic or of a general paretic is a lesion of the nervous mechanism of the pupil ; from a spirochete growing in the nervous system of one host, a spirochete growing only in the nervous system of another host may result. The spirochete in a new host grows best in the tissue from which it is derived. The strain of spirochete is somewhat specific for the tissue it invades, for the tissue in which it grows. McDonagh and Ross state that these strains may be morphologically differentiated; except variations in viability and in the rate of growth in cultural media, no definitely distinctive characteristics have been found by other observers, including Noguchi, Nichols, and Reasoner, to separate these strains.

FIG. 3. — Spirochaeta pallida from the brain of a general paralytic growing in the testis of a rabbit. (Noguchi.)

When a person acquires a spirochete from contact with skin or mucous membrane lesions, the infection soon becomes general and shortly thereafter lesions appear in that person's skin and mucous membranes, heal and recur ; but till the last has finally healed, none as a rule is seen in the deeper tissues.

When the emasculated and less numerous spirochetes invade the deeper tissues, lesions occur there but not elsewhere : the gumma develops alone, unaccompanied by either skin or mucous membrane lesions or by lesions of the central nervous system. So well recognized is this incidence that the rare lesions which contravene the rule are styled precocious. The central nervous system lesions do not occur together with lesions of the deep tissues, nor of the skin and mucous membranes. Spillman and Perrin have reported the occasional occurrence of gummata and even of cutaneous syphilids with tabes and writh general paresis ; but such rare happenings serve merely to emphasize the rule that only one type of tissue is attacked at a time.

Few syphilitics enter matrimony ere the skin and mucous membrane lesions heal. The healthy partner is infected by a spirochete already repelled from the skin and mucous membranes of the infecting partner, a spirochete which can grow with difficulty or not at all in the skin and mucous membranes of the new host. The mildness of the skin and mucous membrane lesions in conjugal syphilis is notorious. The spirochete of the gumma and of the tabetic lesion so rarely produce skin and mucous membrane lesions in another host, that tertiary and nervous lesions are commonly considered to be noninfective.

The spirochete to which a particular tissue or tissues in one host have achieved immunity loses the power to attack that tissue or tissues, not only in the host where the successful defense occurred, but also in any other host, probably to the extent to which the biochemical reactions of the same tissues in the two hosts are identical. The spirochete acquires in the human host characters which enable it to grow best in a certain tissue. If that tissue be the skin and mucous membranes, the spirochete, after growth there, may grow in the deeper tissues ; and, still later, in the central nervous system. If that tissue be not the skin and mucous membranes, then the spirochete's growth is impossible there, but is possible in the deeper tissues, and later in the central nervous system. If that tissue be the central nervous system the spirochete may grow best and only there.

D

Hus band

First Wife

-•Second Wife

Daughter

FIG. 4. — Beaussart's quoted series. D, Non-nervous syphilis; •, syphilis of the central nervous system.

One strain of spirochete which may produce tabes is a spirochete which can grow best or only in the central nervous system; a spirochete which is derived from a host in whom it has been successfully repelled from the skin and mucous membranes and deeper tissues ; a spirochete which causes tabes after no or slight pretabetic lesions, a spirochete which is partly blamable for the many cases of tabes that are ignorant of their infection, and 'for the long accepted but erroneous belief that tabes can develop without syphilitic infection.

Belieres records three cases of general paresis and two of an allied nature that all owed their infection to the same woman. Beaussart quotes a series in which a syphilitic husband, free from nervous affection, had a wife who became tabetic, and a daughter who was a general paretic. After divorce, the husband remarried and his second wife also developed tabes.

Beaussart records a series in which a glassblower, X., acquired a buccal chancre from a drinking cup used by a fellow workman, Y. X. and his wife died of general

Y'sTWife

Y's Wife's Paramour

X's Wife

FIG. 5. — Beaussart's recorded series. O, Non-nervous syphilis; •, • , syphilis of the nervous system.

paresis. Y. died of general paresis. Y.'s wife remained normal but her paramour developed tabes.

Beaussart mentions a man who became a general paretic and whose wife showed taboparesis : her lover developed general paresis and his wife had syphilitic pupillary changes. Morel Lavallee records five cases of general paresis, and Erb five cases of tabes, with a common source of infection. Pierre Marie and Bernard and others have reported similar groups.

In such groups no single source of infection, far less an unique exposure to syphilis, can be established. Yet the larger the group or series of similarly affected cases the greater is the probability that their common experience is also the source of their common mischance. From a common source organisms of an uniform virulence are derived. If in spite of possible differences in dose, in treatment, and in defense, a series of persons infected from a common source acquire nervous symptoms, either a spirochete with a particular faculty to invade nerve tissue is the infecting agent, or several persons, reacting to the ordinary spirochete in the same extraordinary way, are, by a remarkable coincidence, infected from the same source.

Belieres' report makes no mention of nervous affection in the woman alleged to have transmitted the taint ; in Morel Lavallee's series the alleged source of infection did not herself suffer from syphilis of the nervous system; in Beaussart's recorded series, Y.'s wife had no implication of the nervous system. To establish the existence of a special strain of spirochete which can triumph over the average human resistance and finally attack the nervous system, it is, however, not necessary for all exposed to that spirochete to develop syphilitic nervous lesions. If in one series of syphilitics the proportion of cases of nervous disease is greater than the usual proportion in which nervous disease follows syphilis, then a special strain may be acting in that series.

A second analogous series weakens the possibility that persons reacting to spirochete infection in the same unusual manner were coincidently infected, at the same source, by an ordinary spirochete, and increases the probability that the reaction which characterized the series is due to a special invasive power of the spirochete infecting them in common. Every additional series immeasurably enhances this probability. Even the few I have cited demonstrate that there are one or more strains of the spirochete which characteristically persist in spite of the average human resistance, which attack the nervous system, and which maintain this power of attack in transmission from host to host. Perhaps the person in any group free from nervous lesions is the original source of the group infection.

The persisting spirochete is one which can overpower the average human resistance ; or one which, being of average virulence, encounters subnormal resistance ; or one which evades the usual resistance by its inability to attack the outpost tissues.

The persisting spirochete has an attacking force which depends upon its numbers and virulence. With this force the persisting spirochete attacks tissues which are usually safeguarded. Among these protected tissues the central nervous system does not suffer alone ; the cardiovascular and glandular systems are also invaded. The cardiovascular system is invariably attacked: the attack is usually ignored because of the more bizarre and insistent results of the concomitant nervous lesions. But many authors have emphasized the frequency of cardiovascular, especially aortic, lesions in tabes; Matsunaga found fifteen cases of cardiac disease among ninety-nine tabetics. Burr, Grossman, and others have shown the importance of cardiovascular and renal lesions in bringing death to the tabetic. Striimpell has demonstrated the frequency with which patients suffering from aortic and other vascular lesions of syphilitic origin show signs, such as fixed pupils and loss of tendon reflexes, of concomitant syphilitic affection of the central nervous system.

Strains of spirochete which grow best in the central nervous system; poisons, such as alcohol and tobacco, which lower the vitality of the nerve elements ; and constitutional, environmental and occupational influences which render the nervous the most vulnerable system, are the factors that decide that the major attack of the persisting spirochete shall fall on the nervous system.

Attacking force of Liability to syphilis of spirochete central nervous system =

Inherited + acquired resistance.

In the central nervous system the spirochete has no exclusive site of attack.

At least ten per cent of tabetics show optic atrophy. Galezowski found posterior root lesions in 717 out of 1029 optic atrophies. Mott states that fifty per cent of cases of syphilitic optic atrophy end in general paresis. Tabes may change to general paresis. Dejerine states that more than half the cases of general paresis show signs of implication of the posterior roots.

The syphilitic invasion called tabes may advance till much of the central nervous system is implicated.

Oppenheim found in all of the fourteen cases of tabes which he examined endoneuritis or perineuritis in the peripheral sensory nerves. There may be one or several foci in a nerve. Such foci may occur in the secondary stage of syphilis and may not be followed by tabes. Each focus may implicate few or many fibers. The resulting destruction is usually partial and often insignificant. Nonne and others have examined cases in which they failed to find lesions in the peripheral nerves.

Jendrassik, who had a cerebral theory of ataxia to substantiate, declared that a special area of the cerebral cortex was characteristically implicated in tabes. Lesions all over the cortex have been since reported. General paresis may early or late supervene in tabes. Gordon Holmes has shown that tabes may occur without any cortical lesions.

The oculomotor and abducens nerves are usually affected, less often the trochlear; the vagus much more frequently than the fifth; but all the cranial nerves have been found implicated both in their course and in their nuclei of origin.

Together with the vestibular branches of the eighth, and independently, the cerebellum may be attacked.

Not only the vagal but also the sympathetic component of the vegetative nervous system may be extensively diseased in tabes. Of the sympathetic fibers those in the posterior roots are usually attacked. The dorsal sympathetic, as a rule, suffers first and most.

Tabetic foci have been seen in the anterior horn cells as well as among their homologues in the basal nuclei. Such foci are rare and occur late. S. A. K. Wilson states that they are accidental complications of tabes. Lesions in motor nerves have also been occasionally observed.

Homen and Marinesco demonstrated the presence of the spirochete in the lymphatic channels of peripheral nerves. Orr and Rows showed that a communication exists between the general and the cerebrospinal lymphatic systems, at the posterior nerve roots; and that a continuous upward flow of lymph occurs along the peripheral nerves and through the posterior roots. Hence the invasion of the posterior roots was attributed to their accessibility to the spirochete. Poirier found a similar communication in the optic nerve sheath which seemed to explain the liability of the optic nerve to invasion.

But in the olfactory sheath, also, there exists such a communication : another is present in the eighth nerve sheath ; and still others exist where tabetic lesions are infrequent. As the spirochete invasion early becomes general; as sites which enjoy with the posterior roots and optic nerves a communication between the general and the cerebrospinal lymphatic systems do not share with these an equal liability to attack by the spirochete; and as, moreover, Guillain and others, by injection of color-, ing matter, have demonstrated a constant circulation occurring in the cerebrospinal lymphatic system, the distribution of the spirochete probably plays an insignificant role in determining the site of the initial attack.

The main stress of ergot poisoning falls on the posterior roots; of amyl alcohol on the optic nerve; of strychnin and of tetanus toxin, probably, on the synapse of the anterior horn cell. Only local differences in the chemical composition of the nervous system can account for the selection by these several poisons of their respective sites. Such chemical differences may render cultural conditions at one site favorable, at another site less favorable, to the growth of organisms.

Some cells, owing to developmental characteristics, may be less resistant than others ; cells whose processes are unprotected by a neurilemmal sheath may be more vulnerable than others which are sheathed.

Edinger fatigued rats by placing them on a continuously moving treadmill. He then poisoned them with pyridin and found the lesions, although disseminated, mainly in the posterior root zones. In Professor Kraepelin's laboratory, one eye of certain rodents was closed. The open eye was then exhausted by bright flashes of light, recurring every minute, for several weeks. After injecting amyl alcohol into these rodents, one found the optic nerve of the open eye showed greater destruction than that of the closed. It has, therefore, been proved that nerve elements exhausted by excess of functional activity resist less than unfatigued nerve cells, the action of toxic agents. We may infer that neurons exhausted by over-function resist less than those not so fatigued, invasion by organisms.

The amount of stress to which a neuron is subjected depends upon its function and upon its owner's environment. The functioning of sensory neurons, particularly of those which constitute the posterior roots, is almost incessant; whereas, that of motor neurons is intermittent. Sensory neurons are commonly, motor rarely, attacked by the spirochete.

Only unconvincing evidence has been yet offered to prove the influence of occupation in determining the site of the initial lesion, for neurologists have, as a rule, confounded disability due to psychic, with that due to structural, causes. But Hitzig, Oppenheim, and others have emphasized that among the posterior roots those of an injured limb are first attacked; and the frequency with which the vagal and the sympathetic components of the vegetative nervous system are over-stimulated from the mental stress which conduces to tabes may explain why these components are so often found degenerated in tabes.

"Where the spirochete finds the most favorable soil in which to grow and the lowest resistance, it commences

the invasion.

Attacking force of spirochete.

Liability of a neuron to invasion =

Defensive power of neuron.

When an optic nerve is attacked, that optic nerve is at the moment of invasion less capable of defense than the other optic nerve, than the spinal roots, than the cerebral cortex and than any other site.

When two sites in the same nerve, or in different nerves; two optic nerves; two spinal roots; an optic nerve and a spinal root, are equally vulnerable they are simultaneously attacked.

When the attack shifts, it shifts to the next most vulnerable site. It is noteworthy that when the disease starts in one optic nerve, the next site attacked is usually the other optic nerve. Similarly, when the posterior roots are first attacked the disease tends to spread among posterior roots in preference to other sites.

If the optic nerve be the first attacked, the lesions there are usually more severe than if the optic follow spinal lesions.