In children affected with lead palsy the lower extremities are more frequently paralyzed than the upper, due to the relatively greater strain in childhood on the legs than on the arms.
Edinger’s theory, supported as it is undoubtedly by Teleky’s observations, is a matter of the greatest importance in the production of paralysis; for if we accept the view that lead is a poison that has a selective power on certain nerves, we have still to consider which is the greatest force, the selection of certain groups of muscles or the effect of functional action. The theory of muscular overexertion certainly falls in with the type of paralysis, and Teleky has undoubtedly shown that under certain circumstances, by special exertion of other muscle groups not usually affected, these muscles alone, or to a greater extent than those usually affected, are involved in the paresis. If, therefore, lead has a selective action, which is exceedingly doubtful, it must be very slight.
Such selective action is, of course, exceeded by a functional activity which brings about the affection of those nerves which supply the muscles most used. If, therefore, we judge of paralysis as being due to the selective action of lead on certain nerves, we are met at once with the objection that the muscles affected do not always correspond to such a nerve distribution, and that muscles supplied by other than the musculo-spiral nerve are affected by paralysis.
Careful consideration of the chapter on [Pathology], and more particularly of the histological findings described, in which the preliminary action of lead is found to be typically and invariably on the blood, setting up degenerative changes microscopical in size and limited in area, affecting the vessel walls and producing a yielding of the vessel, determining minute microscopical hæmorrhages distributed, not necessarily in one position of the body, but all over the body, and peculiarly in the case of the cat affecting those muscles called upon to perform sudden and violent movement—namely, jumping—enables us to regard such microscopical hæmorrhages as an adequate explanation of the association of paralysis in muscle groups, functionally related to various trades and industrial processes.
It may be argued, and we think with considerable reason, both from pathological and clinical findings, that, as muscular exertion is apparently associated with the onset of paralysis, particularly in those muscles which may be regarded as physically somewhat inadequate to the work they have to perform, and that, as the paralysis is associated with definite functional groups of muscles, and to a curious extent varies according to the trade in which the sufferer is engaged, therefore greater stress thrown upon the muscular tissue at some period or another during occupation determines the microscopical hæmorrhage in the nerve supplying the muscles, or in the muscle itself, so that the paralysis affects just such muscles as have an increased strain thrown upon them. It does not necessarily follow that the preliminary initial hæmorrhage occurring should be a large one—in fact, from the whole of the histological history, hæmorrhages are exceedingly minute; neither does it follow that it is essential for such hæmorrhages to take place in the whole length of the nerve itself; but it is only necessary that the finer branches of the nerve should have their venioles or arterioles affected, and it is of course in the finer branches particularly, as has been pointed out in relation to the venioles, that degeneration of the intima of the vessels takes place.
Finally, the effect of early treatment on lead palsy tends to bear out this theory. If a case of lead palsy be treated in the early stages, the clinical course of the case is good; increased paralysis generally takes place in the first week, and, where, perhaps, only two or three fingers are involved when the case is first seen, spreads generally to other regions within a week, and the whole hand is affected; but from this moment onwards improvement takes place on the application of suitable treatment, and, if continued, almost invariably results in the entire recovery from the paresis.
There is little doubt that this is the true explanation of the ordinary paresis of lead poisoning, and a very great deal more evidence is required to combat it and to prove the selective action of lead upon individual nerves, since the theory of hæmorrhage does not owe its origin to conjecture, but is based on clinical and histological examination of early cases of poisoning.
In attempting to find a cause for the paralysis of the hands so commonly present in painters, it has been suggested that lead is absorbed through the skin, and affects the nerves at their junction with the muscles, setting up a peripheral neuritis [Gombault[8]]. The theory breaks down at once when such commonly-occurring affections as paralysis of the ocular muscles, paralysis of the peroneal type, paralysis of the muscles of the shoulder, etc., are considered.
For the convenience of description lead paralyses are generally divided into a series of groups, the grouping varying according to the function of the various muscles rather than to their anatomical grouping. The various types of paralysis have to be considered in detail: