To take the least important of these first, I may surprise some readers by the statement, which I nevertheless make with much confidence, that irritation of any part of the alimentary canal is, on the whole, a rare concurrent cause, even in the production of neuralgia. There are, as has been already fully explained, cases of neuralgia seated in these viscera themselves (or the plexuses in their immediate neighborhood), although their number is immensely smaller than that of the neuralgias of superficial nerves. But it is not at all common – it is even exceedingly rare – for irritation conveyed from the alimentary canal to take any important part in setting up neuralgia of a distant nerve, even when that nerve has close connections, through the centres, with those coming from the irritated portion of the alimentary canal. Valleix had the great merit to perceive this, even in the case of neuralgias of the head, where appearances are so likely to lead the observer to a contrary opinion. And it is not a little remarkable that this should be the case, when we consider the close central connections which the vagus, the great sensory nerve of a large portion of the alimentary canal, has with the sensory root of the trigeminus. In fact, however, there are certain peculiar forms of gastric irritation which do react upon the trigeminus; for instance, a lump of unmelted ice, suddenly swallowed, almost invariably produces acute pain in the supra-orbital branch of the fifth, on one side or the other, and occasionally (as in a case cited by Sir Thomas Watson) in other nerves. But that common dyspeptic troubles at all frequently or importantly contribute to the production of neuralgia, I do not for a moment believe: it needs some very powerful irritation, such as that just mentioned, or as impaction of great masses of scybalæ in the intestines, or severe irritation from worms, to produce such an effect.
It is far otherwise with the genito-urinary apparatus; in a large number of cases, irritations proceeding from these organs do undoubtedly contribute to the production of neuralgia, though by no means in the important degree which many authors seem to have assumed. There can be no doubt, for example, that the irritation of a calculus, either within the kidney itself, in the ureter, or in the bladder, may set up violent neuralgia, which for the most part is localized in the branches of the lumbo-abdominal nerves. The instance of the eloquent Robert Hall is an example of renal calculus acting in this way: he suffered the most excruciating agony for years, and was obliged to take enormous quantities of opium in order to make life endurable. An instance of calculus impacted in the ureter, in a gentleman somewhat past middle age, occurred in my own practice; the lumbo-abdominal neuralgia occurred in frequent paroxysms of dreadful severity; and another case, already referred to was that of a woman, in whom ovarian neuralgia was undoubtedly in great part due to the irritation of an impacted calculus in the ureter. These cases, however, are very rare in comparison with others in which the peripheral source of the neuralgia is either the uterus or ovary, or the external genitals. I have no means of ascertaining, with anything like accuracy, the frequency with which the internal sexual organs are the starting-point of neuralgia, because the majority of such cases pass, naturally, to the care of physicians who practice chiefly in the diseases of women, and consequently not adequately represented either in my hospital or my private practice; still, I have seen a good many of these affections, and, though I speak with the reserve necessitated by the circumstances just named, I am much inclined to believe that even such powerful centripetal influences as those of the states of commencing puberty, of pregnancy, of the change of life, and uterine diseases generally, are very rarely the cause of true unilateral neuralgia, except in subjects with congenital tendencies to neuralgia. But in predisposed subjects there can be no doubt that these influences assist most powerfully in producing the malady.
Of the power of irritation of the external genitalia to act as a so-called "exciting cause" of neuralgia, there is abundant evidence. I would especially call attention to the remarkable monograph of M. Mauriac, ["Etude sur les Nevralgies Reflexes symptomatiques de l'Orchi-epididymite blenorrhagique" Par C. Mauriac, Medecin de l'Hospital du Midi. Paris, 1870.] on the neuralgias consecutive to blenorrhagic orchi-epididymitis, as illustrating this with a force that was to me, for one, surprising. I shall, perhaps, have further occasion to these researches; here it will be enough to mention that M. Mauriac's enormous experience of blenorrhœa and orchitis at the Midi has shown that, in an exceedingly large number of cases, certainly not less than four per cent., this combination is followed by reflex neuralgias, of which a large number are not seated in the genital apparatus, but affect the track of some distant sensory nerve, through the intermediation of the spinal centres; and that with these reflex pains there is often profound general disturbance, including very often an extremely profound general anæmia. The most frequent kind of these neuralgias is rachialgia, i. e., pain in the superficial posterior branches of spinal nerves; next comes lumbo-abdominal neuralgia; then sciatic and crural, visceralgic (abdominal), etc.; and besides all these there are numerous instances of neuralgia in the testis. As to the nervous "reflection," more hereafter.
It has surprised me, somewhat, that while M. Mauriac has seen so many reflex neuralgias set up by orchi-epididymitis, he does not appear to have noticed cases of trigeminal neuralgia from this source; because, in the very analogous instance of the peripheral irritation produced by excessive masturbation, we undoubtedly do frequently get a development of the tendency to migraine, and also to other forms of neuralgia of the fifth: moreover the effect of such local irritation can be occasionally traced with much distinctness in the trigemini, by a tendency to certain forms of eye-disease without positive neuralgia. This was remarkably exemplified in a case which was under my care some years ago, and in which both eyes were greatly damaged by vaso-motor and trophic changes; partial insanity also supervened with hallucinations of sight and hearing.
We come now to one of the most powerful sources of peripheral irritation tending to set up neuralgia; viz., functional abuse of the eye. This is one of the very few peripheral influences which occasionally we see producing neuralgia unaided by hereditary predisposition, or any other observable cause whatever, and in a far larger number producing it with the sole aid of more or less defective general nutrition. The latter occurrence is well exemplified by a case which Mr. Carter sent me the other day, and which also illustrates (second attack) the effect of the superaddition of syphilitic taint:
Matilda W – , aged thirty-three, married, and has three very healthy children. Comes of a remarkably healthy family, of which she told me the entire history for three generations, with unusual intelligence and clearness. No neuroses, properly so-called, in any of her relatives during all this time. She herself was a very strong and hearty girl until the age of seventeen; between this date and her marriage, three years later, she was obliged to work tremendously hard at fine sewing, by which means she gained a very scanty livelihood. After a comparatively short period of this work she began to suffer from typical attacks of migraine, very severe, and recurring every three or four weeks, but in no particular connection with the menstrual function, which was normal. On her marrying and ceasing to do needle-work, the migraine entirely disappeared, and she retained perfect health till the commencement of 1871. At this time she had suckled a very hearty baby for ten months, and was not able to furnish such good living as usual. She was attacked early in January, with violent neuralgia affecting all three branches of the right fifth, and she the more readily applied for advice because she soon found that the neuralgia was becoming complicated with dimness of vision in the eye of the affected side, "as if she was going to have a cast." Was quite unconscious of ever having had syphilis. The medical man encouraged to believe that the whole malady was nervous, and would soon disappear under appropriate remedies, and gave her quinine, under which treatment she declares that she was rapidly improving, both as to pain and vision, but that her resources came to an end, and she could no longer pay for the medicine. She then neglected herself, and rapidly got worse in all regards, till at last she was compelled to apply to the South London Ophthalmic Hospital, whence Mr. Carter sent her to me, on the 6th of April. At this time the paroxysms were excessively violent and frequent, though brief. On examination, tender points were found at the supra-orbital notch, at the infra-orbital foramen; in front of the ear; in the temporal region; in the parietal region, and the inferior dental region. There was strongly marked anæsthesia of the skin of the right half of the face, of the gums, and of the side of the tongue. The teeth were absolutely perfect: not one spot of caries could be seen. Taste was completely destroyed in left half of anterior part of the tongue. Smell was totally lost on both sides, and had been so, the woman declared, from a very early period in the illness. The right eye showed complete paralysis of the levator palpebræ and of the external rectus; nearly complete paralysis of the superior and inferior rectus, rather less marked paralysis of the internal rectus. Pupil normal, conjunctiva moderately congested, lachrymation profuse, photophobia partial. The functions of the retina were perfect. Accommodation was affected in the following degree and manner. The vision of the affected eye was perfect at long distances, very imperfect at short distances. With both eyes open she saw every thing double, but could still count all the bricks in a whitewashed wall at sixteen feet distant. There was no secondary disturbance of the stomach whatever. On the first visit she assuredly had no visible signs, in skin or throat, of syphilis; the perfect health of her children, and absence of abortions, made syphilis the less probable. But on her second visit she complained of sore throat, and a week later a palpably specific sore appeared on the soft palate. She declared, with apparent sincerity, that it was the first symptom of the kind she had ever had. The neuralgia rapidly disappeared under thirty grains of iodide of potassium daily. The lesions of taste and smell disappeared exactly pari passua with the trigeminal pains. The ocular paralysis threaten to be much slower in departing. I think we must believe that this woman contracted syphilis after the birth of her last child. It is at any rate certain that the migraine of her youth was perfectly unconnected with syphilis, being as unlike the pains evoked by the latter as it is possible for two kinds of pain to be. In all probability she was infected during her last lactation.
Last among the peripheral influences of sufficient importance to be specially mentioned as effective factors in the production of neuralgia, must be mentioned caries of the teeth, and the comparatively rare accident of the mal-position or abnormal growth of a "wisdom-tooth." It is an undoubted fact that these things may cause neuralgia even of a very serious type, and attended with extensive complications; as in Mr. Salter's cases, already mentioned, of reflex cervico-brachial neuralgia from carious teeth. Looking to the extreme frequency of caries, however, as compared with the rarity of true neuralgia (not mere toothache) as a consequence of it, it is impossible not to suppose that the share of the carious teeth in the production of such neuralgia must be very small, compared with that of other influences.
5. The next influence which we shall mention as undoubtedly very effective in assisting the production of neuralgia in certain cases is that of anæmia and mal-nutrition generally; but it is not necessary to dwell on this at any length. The fact is notorious that severe loss of blood is always followed by headache; and if there be the least predisposition to neuralgia, this headache will very commonly take the form of the severest clavus. And, in like manner, chronic states of anæmia and of mal-nutrition undoubtedly aggravate every existing neuralgia, and bring out lurking tendencies to the disease. But I do not believe that anæmia, or starvation pure and simple, ever generates true neuralgia by its sole influence.
6. The question how far, and in what way, the neuralgic tendency is helped by certain constitutional diatheses, such as rheumatism and gout, and by certain toxæmiæ, such as malaria, alcoholism, lead-poisoning, etc., is a very much more difficult one than might be supposed from the off-hand manner in which many writers speak of the "rheumatic," the "gouty," or the "alcoholic" forms of "neuralgia." We may, however, simplify it a good deal. In the first place, it seems obvious to me that the only manner in which alcohol helps the production of true neuralgia is by its tendency, after long abuse, to produce degeneration of the nervous centres: it will therefore be considered, shortly, under another division of the present subject. Lead-poisoning, again, only produces so highly special a form of neuralgia (if colic be neuralgia at all) that it need not detain us here. The influence of malaria is, for the most part, an utter mystery to us, but by so much as we can see it appears plain that one of the most important features in the disease is a powerful disturbance of the spinal vaso-motor centres. But the most interesting consideration that we have to deal with is the question of the supposed relations of the rheumatic and the gouty diatheses, and the syphilitic dyscrasia, to the neuralgic tendency. On this point I am obliged to disagree in toto with the popular view that assigns these diatheses among the most frequent predisposing causes of neuralgia.
To take the case of rheumatism first, I am willing to allow that there are a number of facts which superficially appear to countenance the idea of a close connection of this disease with neuralgia. But of these facts a considerable proportion consist only of examples of inflammation of the nerve-sheath, with a certain amount of effusion within and around it, occurring in persons who have never shown any symptoms which warrant the assumption of a general rheumatic diathesis; and these local phenomena really differ in nothing from many trophic and vaso-motor changes which have been already described as plainly secondary to ordinary neuralgia in which there could be no pretence of a rheumatic pathology except on the slender foundation of a suspicion that the affection was immediately excited by the influence of cold, which is really no argument at all. Such patients will be found to have exhibited, not special rheumatic, but special neuralgic tendencies in their past history. On the other hand, there undoubtedly are a certain number of patients who, having previously given signs of a tendency to generalized rheumatic inflammation of fibrous membranes, are, on some particular occasion, attacked with similar inflammation extending over a more or less considerable tract (not a small limited spot) of a nerve sheath. But so far from agreeing with those who think that this is a frequent case, my experience teaches me that it is quite exceptional; nor do I believe that the common opinion could ever have arisen had it not been for the rage that exists for connecting every disease with a special diathesis which the profession flatters itself that it understands. Few persons have taken more pains than myself to ascertain the frequency with which neuralgic patients show a history of previous rheumatism, whether in the so-called "fibrous," or in the synovial form; but it is remarkable how seldom I have found this to be the case – a result which surprised me, because it happened that I, a neuralgic subject, had suffered in youth from regular acute rheumatism, and had fancied that I should discover a close connection between rheumatism and neuralgia. Eulenburg states that neuralgia caused by cold more frequently attacks the sciatic nerve than any other, and thinks that the tendency to sciatica is characteristic of the relations of rheumatism to sensory nerves. For my own part, I see no reason to call in the rheumatic diathesis as a deus ex machina to explain the frequency with which sciatica follows comparatively trifling peripheral impressions like that of cold. The true reason I believe to be, that what would have been a slight and trivial neuralgia elsewhere, becomes a serious affection in the instance of the sciatic nerve, by reason of the strong muscular pressure end dragging which are always going on in the thigh in locomotion. I shall return to this subject when speaking of Treatment.
As regards the relations, of gout to neuralgia, I can hardly express my own view better than by quoting the words of Eulenburg:17 "Much more doubtful is the influence of gout, which in rare cases, perhaps, produces neuralgia directly, by means of neuritis, or by the deposit of tophus-like calcareous concretions in the nerve-trunks. Gout has been reckoned as a great influence among the causes of superficial neuralgias (sciatica), and also of visceral neuralgia (angina pectoris, etc.,) but this influence is more probably only an indirect one, operating through circulation changes which are often produced by chronic liver-diseases or by diseases of the heart and vessels, (e. g. Valvular diseases and narrowing of the coronary arteries in angina)." To which I will add this argument against any close connection of gout with neuralgia, that it is exceedingly seldom that colchicum effects any decided good, a fact which is as unlike the relations of colchicum to true gout as any thing could be. For, whatever may be thought of the advantages or disadvantages, on the whole, of employing colchicum against gout, at least no one with any experience will deny that in the immense majority of cases of true gouty pain, it gives rapid relief to the acute suffering. I doubt if it ever18 acts in that way in real neuralgia, though I have occasionally seen it apparently useful in a more limited way, as will be said hereafter.
As regards the relation of the syphilitic dyscrasia to neuralgia, I agree in general with Eulenburg. "Syphilis," he says, "may be the direct cause of neuralgia, either by the development of specific gummata in the nerve-trunks or in the centres, or by arousing chronic irritative processes in the nerve sheaths, the membranes of the brain and spinal cord, or, especially, in the bones and periosteum (syphilitic osteitis and periostitis)." The case of periostitis, however, is a doubtful one: it may be questioned whether this affection (which will be among the diseases discussed in Part II. of this work) ever give rise to true neuralgia. Persons who are, by inheritance, highly predisposed to neuralgia, may from the mere general lowering of their health produced by constitutional syphilis, become truly neuralgic simultaneously with, or subsequently to, the appearance of painful nodes on their bones. And as regards the whole relations of syphilis to neuralgia, I must, from my experience, conclude that the former is, after all, but rarely concerned in the production of the latter. Syphilis has a strong specialty for producing limited motor paralyses, but a much weaker one for producing limited affections of the sensory system.
7. We now come to the discussion of a group of momenta whose influence in the production of neuralgia is at once very powerful, and of the highest significance as regards the general pathology of the disease. These are the degenerative changes of the arterial and capillary systems which are a part of the normal phenomena of old age, but may occur at earlier periods of life, in consequence either of certain constitutional diseases, especially gout, or of special toxic influences on nutrition, of which persistent alcoholic excess is very far the most important.
The reader does not need to be told the familiar story of the degenerative changes in the vessels which, commencing usually some time during the fifth decenniad, by degrees convert the elastic arterial coats, and the almost membranous walls of the capillaries, into more or less rigid tubes; nor does he need to be informed that the tendency of these changes, as they operate in the great motor and intellectual centres, is notoriously to produce innutrition of the tissues that depend for their blood supply on the affected vessels, whence cerebral softening so commonly results. That analogous changes take place in the vessels supplying the spinal centres is certain; but it is a remarkable fact that these do not very commonly produce motor paralysis. What they do produce is rather a slow enfeeblement both of (spinal) sensation and motion, but where the process of decay has been prematurely forced, or the inheritance of neurotic weakness is very marked, the process of sensorial decay (the decline, that is, of true sensorial function) is apt to be mingled with pain. That this pain should be localized, often in a single nerve, is no more surprising than the fact that the degenerative process itself should vary so greatly in the degree of its development at one point from that which it shows at others. I have already insisted (vide Chapter I.) on the marked correspondence between the period of life in which degenerative changes commence and progress (the last third, roughly speaking, of a fairly long life), and that in which the most severe, intractable, and progressively increasing neuralgias are developed. I must here notice a singular statement of Eulenburg's, that neuralgia never attacks people who are over seventy. That statement shows that persons of a greater age than seventy are rare in this world, and that no such patient happened to come under Eulenburg's notice; for I have (by mere chance, doubtless) seen several instances of first attacks occurring after seventy; and almost the worst case of epileptiform tic I ever saw began when the patient was eighty; she was a member of a highly neurotic family whose medical genealogy is given at a previous page. In general terms, it may be said that every additional year of life after fifty increases the probability that a neuralgia, should such arise, will be severe and rebellious to treatment; and in the very aged the cure of such affections is probably impossible.
8. This seems the proper place to introduce such facts as have been observed, and they are very few, that directly illustrate the material changes occurring in neuralgia.
Very much the most important of these facts is the history of a remarkable case recorded by Romberg. ["Diseases of Nervous System," Syd. Soc. Trans., vol. i.] The patient, a man sixty-five years old at the time of his death, had suffered for several years from the most violent and intractable epileptiform trigeminal neuralgia, complicated with interesting trophic changes of the tissues. Post-mortem examination showed that the pressure of an internal carotid aneurism had almost destroyed the Gasserian ganglion of the painful nerve, that the trunk and posterior root of the nerve were in a state of advanced atrophic softening, and the atrophic process had extended in less degree to the nerve of the opposite side. Now, the value of this case is by no means restricted to the fact that it records the existence of a particular anatomical change in one example of neuralgia. Its most striking teaching is the fact that the acutest agonies of neuralgia can be felt in a nerve, the central end of which is reduced to such a pitch of degeneration that conduction between centre and periphery must very shortly have entirely ceased had the patient lived. And hardly less important is its illustration of the fact that permanent injury to the ganglion of the posterior root of a spinal nerve impairs the vitality of the posterior root itself – a fact which has been independently made out by the physiological researches of Bernard and of Augustus Waller.
On the other hand, if we examine the tolerably numerous histories of cases in which the painful nerves have been examined at the apparent site of pain, we discover nothing to lead us to connect neuralgia definitely with any one sort of change. Assuredly, for example, local neuritis is by no means universally, it is probably even not commonly, present in the early stages of neuralgia; it has also been repeatedly detected in nerves that had been wholly free from neuralgia; and, on the other hand, it has been entirely absent in nerves that have been the seat of the severest pains. Moreover, many facts which have been put down without reflection, as showing a local peripheral cause for neuralgia, are at least open to another and, as I believe, truer explanation; as (e. g.) in the following remarks of Eulenburg on mechanical irritations of nerves as causes of neuralgia: "Diseases of bones are extraordinarily frequently the cause of neuralgias in consequence of compression or secondary disease, which affects the branches of nerves passing through canals, foramina, fissures, or over processes of bone. The appearances which the opportunities of resections of the trigeminus for facial neuralgia have permitted to be discovered, have given us valuable information in that direction. Flattening and atrophy of nerves from periostitis, or from concentric hypertrophy in narrowed bony canals, have frequently been discovered. The neurilemma at the narrowed parts was often seen reddened, ecchymosed, infiltrated with serum, or surrounded with fibrous exudation; occasionally inflammation had been followed by partial thickening of the neurilemma (fibrous knots) and turbidity (Trubungen) of the nervous cord at the corresponding spot. Similar appearances have been noted in other neuralgias (neuralgia-brachialis, sciatica)." For my own part, I believe that the above description represents the facts from an erroneous point of view. True neuralgia, if by that we understand a pain of intermittent character limited to one or more nerves, is in my experience an extremely uncommon result of periosteal disease, or of inflammation of the linings of bony canals; but in a great number of instances such diseases appear to be set up as the secondary consequence of the neuralgic process (whatever the essential nature of that may be) going on in sensory nerves which supply the parts when these inflammations appear. And it must be remembered that the specimens obtained by resection of nerves are comparatively few in number, and are taken universally from old-standing and desperate cases of disease; in short, from cases which are just in those advanced stages of neuralgia in which, as has already been amply shown, these secondary inflammations are almost always present. On the other hand, I have myself had one opportunity of examining the local condition of an intercostal nerve, which during life, and quite up to death, had been the site of the most pronounced neuralgia, which, however, had only existed for a few days. The patient, a young man, aged twenty-seven, was probably insane, and had attempted suicide. Not a trace of inflammation, either in the nerve itself or in any of the tissues to which it was distributed, could be detected. (This was a case in which I greatly regretted the impossibility of getting a family history that was at all reliable.) The spinal cord, unfortunately, could not be examined. And I strongly believe, from the marked absence of tenderness on pressure which is almost universally observed in ordinary cases of neuralgia at an early stage, that primary inflammation of neurilemma, periostem, etc., as a cause of neuralgia, is altogether exceptional; so much so, that we are entitled to believe it can never be more than a concurrent, and then not the most important, cause.
It is necessary here to inquire, more particularly than we have yet done, into the nature of the "painful points" first signalized by Valleix as a distinctive symptom of neuralgia. Very great differences of opinion have prevailed among subsequent writers, both as to the frequency and the significance of these points. It may be said, however, to be now quite settled that the presence of definite points, painful on pressure, and also corresponding to the foci of severest spontaneous pain, is far from universal in neuralgia. Upon this point there is probably no reason to doubt the correctness of Eulenburg's observations made in the surgical clinic of Greifswald and the polyclinic of the University of Berlin; he says that he discovered the existence of tender points in "Valleix's sense," in rather more than half the cases of superficial neuralgia, but in the rest he could not by any means discover them. In many other cases, however, he found more indefinite points of tenderness, not accurately corresponding to nerve-branches, but affecting individual portions of skin, bone, or joints; the relation of these to the neuralgic symptoms was difficult of explanation. Eulenburg lays down the principle that "hyperæsthesia" may depend on three sorts of causes – (1) On local disease of the peripheral ends of nerves; (2) on alterations of the psychical centres; and (3) on morbidly exaggerated conduction in the nerve-trunks themselves; and it is to this third source that he attributes many of the phenomena of the neuralgic painful points, and especially their multiplicity, in many cases. The locus in quo of the mischief which sets up this exaggerated conduction of sensory impression is, upon this theory, between the psychical centre and the main point of branching of the nerves; hence a large number of peripheral nerve-termini might be practically sensitive to touch, because the mischief, though localized in a comparatively small spot, might easily affect many bundles of fibres, which diverge widely from each other in their course. It will be seen presently with what limits and for what reasons we believe this to be a true theory. But to return to the question of painful points in Valleix's sense, we must state one or two facts which seem certain from our own experience, but have not been adequately recognized, we believe, by others. The first is, that localized tender spots, accurate pressure on which will set up or aggravate the neuralgic pain, are not early phenomena, save in neuralgias of exceptional severity of onset; but that a certain persistence and severity of neuralgia are always followed by the formation of one or more true points douloureux. The second fact relates to the clinical history of migraine. Roughly speaking, it is true, as Eulenburg states, that, in pure migraine, painful points in Valleix's sense are not to be found; in place of them we observe, after the paroxysms have passed away, a more generalized soreness of considerable tracts of the scalp, forehead, etc., or diffuse tenderness of the eyeball. But I must here again refer to the fact, first observed in my own case, and afterward verified in many others, that migraine may be only the youthful prelude to a regular trigeminal neuralgia attended with the formation of characteristic localized painful points at a later period. And the third fact that must be specially mentioned is that the true Valleix's point, when it has become established for some time, is not a mere spot of sensitive nerve, but is the scene of trophic changes, involving hyperæmia and thickening of parts surrounding the nerve. To give one example, it is quite a frequent thing to find a patch of tender and sensibly thickened periosteum of irregular shape, but equal sometimes to a square inch in size, over the frontal bone at and immediately above the inner end of the eyebrow, in cases where supra-orbital neuralgia has recurred frequently during some years, although no such thing was present when the neuralgia first commenced. In my own case, the bone has become sensibly thickened at that point.