5. Impairments of sensation, both common and special, are very frequent attendants of neuralgia. As regards the special sensations, we may first mention that of touch; this is almost constantly impaired, immediately before, during, and some little time after a neuralgic paroxysm, in the skin supplied by the painful nerves. I was first led to make this observation by my own experience; the skin all round the inner angle of my right eye is permanently less sensitive to distinctive impressions than that of the opposite side, and this impairment is always decidedly greater, and spreads over a larger surface, before, during, and for some time after, the attacks of pain. More extended observation has convinced me that a certain amount of bluntness of distinctive skin-sensation accompanies nearly every neuralgia. As regards the sense of taste, I have found this decidedly perverted, at the time of an attack, even in my own case, although the neuralgia never extends into the third branch of the nerve. It is interesting to notice, in connection with this, that the epithelium of my tongue has been seen, on one occasion, to be exaggerated on the side of the neuralgic affection, showing a probability that there is perturbed function, at any rate of certain fibres, of the third division. But I have seen much more decided alteration, indeed temporary entire abeyance of the power to distinguish between the tastes of different substances, with the affected side of the tongue, in a case of severe epileptiform tic in which the third division was strongly affected with neuralgia; and Notta records a similar instance. As regards vision, besides minor perversions and disturbances, I have observed more or less complete amaurosis in several instances of ophthalmic neuralgia; in one case it was absolute, and lasted, with but slight improvement in the intervals between the paroxysms, for nearly a month, but disappeared entirely, though somewhat gradually, after the final cessation of the neuralgia. As regards hearing, I have noticed serious impairment only in five cases, all of them of a severe type of trigeminal neuralgia, involving all three divisions of the nerve. Smell, I have never observed to be more than doubtfully impaired, except in one case (vide Chapter III), where it was completely destroyed.
Common sensation was reported by Notta as affected in only three cases out of a hundred and twenty-eight; but my own experience has afforded a much larger proportion of instances in trigeminal neuralgia. Indeed, in all situations neuralgia appears to me to involve this effect, in the larger number of instances, in the early stages; later, it is supplanted in part by great tenderness on pressure in the well known points douloureux, and sometimes the tenderness becomes diffused over a considerable surface. I agree with Eulenburg in thinking that anæsthesia is more frequent in sciatica than in other neuralgias.
6. Secretion is often very notably affected in neuralgia; the phenomena are necessarily more easily observed in connection with affections of the trigeminal than of other nerves. In the great majority of cases the affection is in the direction of increase; at least, the watery elements of secretion are often poured out in profusion. Thus, profuse lachrymation is exceedingly common in ophthalmic neuralgia; in a large number of cases there is also copious thin nasal flux on the affected side; sometimes, however, the secretion, though copious, is semi-purulent, or bloody. Increased salivation has been noticed, by a large number of observers, in neuralgia involving the lower division of the fifth. In a smaller number of instances, the secondary effect on secretion is precisely opposite; thus both Notta and myself have observed complete dryness on the nostril on the affected side in ophthalmic neuralgia.
I might expand this chapter on the complications of neuralgia to a very much greater length; but, as regards the clinical history of these affections, it is perhaps better not to occupy more time and space. It will, however, be necessary to return to the consideration of the subject in connection with Pathology.
CHAPTER III.
PATHOLOGY AND ETIOLOGY OF NEURALGIA.
The pathology and the etiology of neuralgia cannot be considered apart; they must be discussed together at every step. I do not mean to say that neuralgia is singular among diseases in this respect; it seems to me merely a case in which the intrinsic defects of the conventional system of separating the "causes" of disease from its pathology happen to be more glaring and more easily demonstrable than usual.
Neuralgia possesses no "pathology," if by that word we intend to signify the knowledge of definite anatomical changes always associated with the disease, in a manner that we can exhibit or exactly describe. It also possesses no demonstrable causes, if we employ the word "causes" in the old metaphysical sense. And yet I am very far from admitting, what seems to be so generally taken for granted, that we know less about the seat, the nature, and the conditions of neuralgia than of other diseases. On the contrary, I believe, with all deference to the supporters of the ordinary opinion, that we know more about neuralgia, in all these respects, than we do about pneumonia, only our knowledge is not of the superficial and obvious kind, but requires the aid of reason and reflection to develop and turn it to account. It has long been a matter of surprise to me, that even able writers have been content to talk about this disease (as, indeed, they have been content to speak of many nervous diseases) with an inexplicable looseness of phraseology. They speak of its "protean" forms; whereas, in my humble judgment, its forms are by no means specially numerous. They insist on the mysterious and unintelligible manner of its outbreaks, remissions and departure; but I shall try to show that, although, in the investigation of neuralgia, we are continually stopped in particular lines of inquiry by what seems to be ultimate facts, susceptible of no further immediate solution, the channels of information open to us are so unusually numerous as to enable us to accumulate a mass of information which, upon further reflection, will be found to furnish the materials of a synthesis of the disease singularly clear and effective for every practical purpose of the physician. In one important particular I especially hope to convince the reader that a large proportion of the mystification as to the pathology of neuralgia is gratuitous, and the result of great carelessness in estimating the comparative value of different facts. I hope to show clearly that, as regards both the seat of what must be the essential part of the morbid process, and the general nature of the process itself, we possess very definite information indeed. I expect, in short, to convince most readers that the essential seat of every true neuralgia is the posterior root of the spinal nerve in which the pain is felt, and that the essential condition of the tissue of that nerve-root is atrophy, which is usually non-inflammatory in origin. This doctrine seems, at first sight, presumptuous,[16] in the confessed absence or extreme scarcity of dissections which even bear at all upon the question. But one source of the extraordinary interest which the pathology of neuralgia has long possessed for me resides in this very fact, that I am convinced we can demonstrate the above apparently difficult theorem by means of pathological observations on the living subject, taken in conjunction with physiological experiments, and with only the aid of a very few isolated facts of positive morbid anatomy. I need hardly say that I am none the less anxious for that further assurance which we shall one day, perhaps, obtain by means of greatly-improved processes for microscopic detection of minute changes in nerve-centres; but, looking to the necessary rarity of opportunities for post-mortem examinations of the nervous system in any but the most advanced stages of neuralgias, it will hardly be disputed that, if I am right in my main position, we are singularly fortunate to be so unusually independent of the need for this source of information.
1. The first fact which strikes me as of decided importance is the position of neuralgia as an hereditary neurosis; and this character of the disease is so pregnant with significance, that I shall take some considerable pains to put the fact beyond doubt in the reader's mind.