(see Lead Poisoning). The course of the disease is long, and an
attempt should be made to eliminate the lead from the system by
purgatives and the administration of potassium iodide.
The diabetic neuritis paraesthesia is slight, and the legs are chiefly affected; weakness and ataxia may be present. Trophic sores on the feet are of frequent occurrence in this variety. The treatment is that of the disease.
Post-diphtheritic neuritis occurs in about 10% of all cases of diphtheria. In this form paralysis of the soft palate is the earliest symptom, and this may be the only one, or the pharynx may be affected. The limbs are affected much later, usually about the 5th or 6th week. Atrophy of the muscles is frequently rapid. If the respiratory muscles are unaffected the prognosis is good, but the paralysis of the limbs may last for several months. The treatment is complete rest, good food and the administration of strychnine.
Acute polyneuritis with numbness and motor weakness has been noted after influenza, together with slight muscular wasting and electrical degeneration. Later, loss of sensation in the peripheral portion of the limbs is complained of, and the motor weakness may affect the muscles of the trunk and face. Such cases tend towards complete recovery.
NEUROPATHOLOGY, the general name for the science concerned with diseases of the nervous system. As regards the anatomy and physiology, see the articles Nerve, Nervous System, Brain, Spinal Cord, and Sympathetic System. The morbid processes affecting the nervous system are numerous and varied, but usually they are clinically divided into two great groups of (1) organic disease, (2) functional disturbance. Such a classification depends upon whether or not symptoms observed during life can be associated with recognizable changes of the nervous system, gross or microscopical, after death. Sometimes this is the morbid process itself, sometimes only the ultimate result of the process. It must be remarked, however, that many diseases which we now look upon as functional may be found due to recognizable changes when suitable methods of investigation shall have been discovered. The paroxysmal neuroses and psychoses may be considered a priori to be due to temporary morbid functional conditions. Our knowledge of the first group is naturally much more advanced than of the latter, for, given certain symptoms during life, we are able, as a rule, to predict not only the nature of the morbid process, but its particular locality.
The histological elements which make up the nervous system may also be divided into two groups: (1) the nervous units or neurones, (2) the supporting, protecting and nutrient tissues. Organic diseases may start primarily in the nervous units or neurones and cause their degeneration; such are true diseases of the nervous system. But the nervous units may be affected secondarily by diseases starting in the supporting, protecting and nutrient tissues of the nervous system; such are essentially diseases within the nervous system, and include diseases of the blood-vessels, lymphatics, membranes and the special nervous connective tissue, neuroglia (a residue of the embryonal structure from which the nervous system was developed). Tumours and new growths must also be included.
The modern conception of the “neurone” as an independent complex cell with branching processes, in physiological rather than anatomical association with other neurones, has modified our ideas of the morbid processes affecting the nervous system, especially as regards degenerations of systems, communities or collections of neurones subserving special functions. It was formerly believed, and generally taught, that the primary systemic degenerations were due to a sclerosis; thus locomotor ataxy was believed to be caused by an overgrowth of the supporting glia tissue of the posterior columns of the spinal cord, which caused a secondary atrophy of the nervous tissue. We now know that this overgrowth of glia tissue is secondary to the atrophy of the nervous elements, and the only true primary overgrowth of glia tissue is really of the nature of the new growth (gliosis). But even in this case it is doubtful if the mere proliferation of the glia tissue elements could destroy the nervous elements, if it were not for the fact that it leads to changes in the vessel walls and to haemorrhages.
The symptoms manifested during life depend upon the nature of the morbid process and the portion of the nervous system affected. A correct understanding of neuropathology involves the study of (1) the causes which give rise to morbid conditions, which are often complex and due to various combinations of factors arising from without and within the body, and (2) the changes in the structure and functions of the nervous system brought about by intrinsic and extrinsic causes.
The causes of pathological processes occurring in the nervous units (neurones) may be divided into internal and external, and it may be remarked that in all cases except direct injury the two groups are generally more or less combined.
A. Internal Causes.—Of all the causes of nervous disease hereditary predisposition stands pre-eminently first; it may be convergent, paternal, maternal; from grandparents or even more remote ancestors. Moreover, no study of heredity is complete that does not take into consideration collaterals. Especially does this statement apply to functional neuroses, e.g. epilepsy, migraine, hysteria and neurasthenia; and to psychoses, e.g. delusional insanity, mania and melancholia, manic-depressive, recurrent or periodic insanity and dementia-praecox or adolescent insanity.
In 70% of 150 cases of idiocy or imbecility in the London county asylums, Dr Tredgold found a family history of insanity in some form or another. Strictly speaking, it is the tendency to nervous disease rather than the disease itself that is inherited, and this is frequently spoken of as a neuropathic or psychopathic taint. There are, besides, a number of inherited diseases, which, although somewhat rare, are of interest inasmuch as they affect members of a family, the same disease frequently commencing in each individual at about the same age. These are termed family diseases, and include hereditary ataxia (Friedreich’s disease), myotonia (Thomsen’s disease), hereditary (Huntingdon’s) chorea, amaurotic idiocy and various forms of idiopathic muscular atrophy. Alcoholism, tuberculosis and syphilis in the parents, especially if one or both come from a neuropathic or psychopathic stock, frequently engender idiocy, imbecility, epilepsy and general paralysis in the offspring, by the production of defects in the vitality of the germinal plasm, causing arrest, imperfect development or premature decay of groups, communities or systems of neurones, especially those which are latest developed—the symptoms manifested depending upon the portions of the nervous system affected. To explain the hereditary neuropathic tendency morphologically, we may suppose that there is an inherited defect in the germinal plasm which is concerned in the formation of the neurones. We may regard the neurone as a complex cell, and the nervous system as a community of neurones arranged in systems and groups having special functions. Like all cells, the neurone nourishes itself and is not nourished; certainly it depends for its development, life and functional activity upon a suitable environment, but it must also possess an inherent vital energy by which it can assimilate and store up nutrient material which may be regarded as potential (latent nerve energy), to be converted into nerve force as required. A constant constructive and destructive bio-chemical process occurs in the neurones of a healthy nervous system, latent nervous energy is high and the sense of fatigue is the natural indication for sleep and repose, whereby it is constantly recuperated. In the neuropathic or psychopathic individual it may be conceived that in some portion of the nervous system, especially the brain, there may exist communities, systems or groups of neurones with inherited low potential, readily becoming exhausted, and, under the influence of altered blood states or stress, especially liable to functional depression, from which arise function-paralysis and melancholia. Again, the bio-chemical substance which represents potential in the nervous system may be in a chemically unstable condition, so as readily to fulminate when excited by abnormal conditions (e.g. toxic conditions of the blood), thus acting as a centre of discharge of nervous energy, which may be manifested by mental or bodily symptoms. We know that in strychnia and tetanus poisoning the most localized peripheral excitation will cause general muscular spasm; in both toxic conditions the spread is probably due to a bio-chemical change in the protoplasm of the spinal neurones, whereby the excitability is greatly increased and a slight stimulus is sufficient to fulminate the whole system of motor neurones. In epilepsy and other paroxysmal neuroses and psychoses it is possible that some altered condition of the blood, when associated with an inherited bio-chemical instability of certain groups, systems or communities of neurones, may act as a fulminating agent. In neuralgia and local hyperaesthesia the slightest general or distant local irritation suffices to produce pain; thus coughing, the vibration of a passing train or the slamming of a door may produce pain by the stimulation of the hyper-excitable neurones. Moreover, it must be borne in mind that the symptoms of nervous disease are due as much to normal physiological functional activity improperly applied, as to actual loss of function occasioned by disease. Thus squint, caused by paralysis of one of the muscles of the eyeball, causes less trouble to the patient than the double vision occasioned by the physiological activity of the two retinae, upon the corresponding points of which the images are prevented by the paralysis from falling.
