The effect of treatment, or rather its want of effect, usually affords powerful assistance in distinguishing the pains of locomotor ataxy from those of true neuralgia. Even where the pain has been fixed for some hours in a single nerve, and has been stopped by some powerful remedy (such as hypodermic morphia), it will be apt speedily to recur, and frequently in some quite distant nerve.
Locomotor ataxy is a disease affecting chiefly the male sex, and occurring in the immense majority of cases between the thirty-fifth and the fiftieth year.
Not merely is it strictly limited to individuals who belong to families with neurotic tendencies, but it is itself frequently seen to occur in several members of the same family, and sometimes of the same generation. When, therefore, we meet with neuralgic pains of the shifting type above described, it is very important at once to make careful inquiries whether any members of the family have suffered from symptoms of ataxy going on to a fatal result. Otherwise, we might be the more readily deceived into the idea that the pains were merely neuralgic, because the symptoms of the disease are not unfrequently provoked by such causes as fatigue and exposure to cold or wet, which are also very ordinary exciting causes of true neuralgia.
[49] The most complete and careful work of the German school, on this subject, is the "Lehre von der Tabes dorsualis," of E. Cyon. (Berlin, 1867.)
[50] _Lancet_, June 10, 1865. (Comment on a case of Dr. J. Hughlings Jackson's.)
[51] Radcliffe, in "Reynolds's System of Medicine," vol. ii.
Cerebral abscesses is, fortunately, a rare disease; but the very fact of its rarity makes the resemblance of the pain it causes to that of neuralgia the more likely to lead us into serious errors. We are apt to forget the possibility of suppuration of the brain on account of its infrequence.
Pain in the head is present as an early symptom of abscess in the brain in a large proportion of cases in which there is pain at all. [Of seventy-five cases of cerebral abscess analyzed by Gull and Sutton (Reynolds's "System of Medicine," vol. ii.), pain was a symptom in thirty-nine, and most frequently an early symptom.] Many cases are recorded in which it preceded every other morbid sign by a considerable period. It is usually more or less paroxysmal, often strikingly so; in the latter case, it bears a great similarity to neuralgia. On the other hand, it sometimes takes the shape of a fixed burning sensation, much less resembling neuralgia. The situation of the pain by no means always, nor even usually, corresponds to the situation of the cerebral abscess; on the contrary, abscess in the cerebellum has often caused pain referred to the anterior part of the head, and so on. So long as the disease remains characterized only by pain, more or less, of a paroxysmal character, the diagnosis must be very uncertain; but in the great majority of cases certain more distinctive symptoms soon become superadded; either convulsions (sometimes hemiplegic), vertigo, coma, paralysis, vomiting, or a combination of some of these.