Lead poisoning and lead absorption

by Sir Thomas Morison Legge; Kenneth Weldon Goadby

(b) Retardation of the general oxidation changes of the body, resulting in malnutrition and general loss of tone.

(c) Establishment of intoxication, with the generalized affections, paresis, etc.

If three such periods can be recognized, as no doubt they can, as divisions of the time during which lead gradually affects the tissues, the symptoms in the more severe cases would be expected to be those associated with the more prolonged exposure. This, no doubt, is true to a limited extent, more particularly in industrial poisoning, depending for its development on a long-continued dosage of lead in minute quantities, and for the most part of metallic lead. On the other hand, with some of the salts of lead, notably the hydrated carbonate, acute disease may take place during the first stage—namely, impregnation of lead—the determining factor then being either the retardation of the elimination of lead, or a suddenly increased quantity in lead dosage, or some intercurrent disease, or even alcoholic excess, whereby a sudden large excess of the poison is thrown into the general circulation.

The commonest type of paralysis occurring is the one affecting the muscles of the hands, which may for a considerable time show some diminution in their extensor power before the actual onset of the disease takes place. The onset of paralysis is practically always unaccompanied by pyrexia; the only occasions in which pyrexia may be associated with the onset of the attack are those cases in which some secondary cause determines the paralysis, and the pyrexia in these instances is due to the intercurrent disease, and not to the lead infection.

Although weakness of the extensor muscles of the hands may be present in persons subjected to lead absorption for a considerable time, the actual onset of the disease itself is frequently sudden; but in the majority of cases it is distinctly chronic, and is rarely, in the case of paresis, associated with any definite prodromal symptoms. Prodromal symptoms have been noted, such, for instance, as lassitude, general debility, and more especially loss of weight. Cramps of the muscles the nerve-supply of which is becoming affected, alteration of the skin over areas corresponding to definite cutaneous nerves, hyperæsthesia, anæsthesia, or analgesia, may occasionally be present. Neuralgic pains have also been described, but these are inconstant, and generally of the arthralgic type related to the periarticular tissues of joints rather than to pain in the course of the nerves. The pain is rather of the visceral referred type than a definite neuralgia. Tremor is, however, frequently associated with the preliminary condition of paresis, and in several cases variations in the amount of weakness of the extensor muscles of the wrist have been noticed, as far as can be estimated clinically without the use of a dynamometer. Associated with this weakness is tremor of a fine type, often increased by movement (intention tremor), and in every case more marked during the periods of increased weakness. Instances have occurred where definite wrist-drop followed after a prolonged period of weakness; in others the weakness has temporarily cleared up for six months, and no difference could be determined in the extensor power of the two wrists; while in others, again, the weakness is progressive, but slight, and insufficient to warrant the removal of the workman from his occupation. Again, progressive weakness may remain a symptom of the wrists of workmen for years.

The Forms of Lead Paresis.

—The paralysis may be partial or generalized, but the chief muscles affected are the extensors of the wrists and the forearm, and the interossei of the hand. As a rule, the first muscles to be affected are the extensor communis digitorum and the extensor indicis. The muscles of the shoulder—mainly the deltoid—come next in order, followed by the muscles of the leg, particularly the peroneus longus and brevis, with occasionally the interossei of the foot; the muscles of the back, neck, and abdominal walls, are occasionally affected, as are those of the larynx and diaphragm, and it is of interest to note that Trousseau pointed out that among horses employed in lead works paralysis of the superior laryngeal nerve often occurred.

Considerable difficulty is experienced in estimating the reason of the predilection of lead for the musculo-spiral nerve, this being the nerve mainly affected in wrist-drop. Owing to the fact that the supinator longus receives an additional nerve-supply to the musculo-spiral, this muscle frequently escapes paralysis when the whole of the other extensors of the hand are involved. Moreover, the predilection for given nerves differs in different animals, and one of us (K. W. G.) has found experimentally that in cats the first nerve to be affected is the anterior crural supplying the quadriceps extensor, whilst the second group of muscles affected are the spinal muscles, particularly in the lumbar region.

Among the speculations which have been made with regard to this predilection for definite groups of muscles supplied by one nerve, Teleky[4] examined forty cases of paralysis with special reference to Edinger’s theory—namely, that the function of muscles (and of other organs) breaks down under certain circumstances before the strain set upon them. In this way Edinger explains paralysis following lead poisoning as being due to excessive strain on the particular group of muscles affected, based on a consideration of the relative volumes and weights of the muscles of the hand and forearm, and the demands made on the several groups, flexors, extensors, supinators, etc., by the coarse or fine work respectively demanded of them in industrial employment. He concludes that—

1. Of the forearm, the flexors (triceps, anconeus, extensors, biceps, brachialis anticus, and supinator longus) possess a high degree of capacity for work, but are not called into play mainly in the execution of fine work; while the supinators are characterized by great mass, and are brought into play mainly in work of coarse and heavy nature, and not during fine manipulations.