The length of time over which habitual exposure to lead without the development of palsy may extend was found by the same observer to vary from eight days to ten, twenty, or even twenty-five years. One individual first suffered from paralysis after fifty-two years of exposure.
Without dwelling upon the sources of error in statistics of this kind, it must be conceded that they establish in a general way the extraordinary differences in the susceptibility of individuals. There are persons who every time they are attacked with colic, of whatever degree of severity, suffer also from paralysis. Others, on the contrary, suffer from repeated attacks of violent colic without the development of paralysis.
Lead palsy is an affection of adult life. Of 102 cases, 2 only occurred in individuals below twenty years of age.
Like the other specific lead affections except the encephalopathy, palsy is more common in the summer than at any other season.
Those who have once suffered are very liable to successive attacks. Tanquerel and Maréchal have observed many returns of paralysis, presenting the characters of the original attack, many years after the patient had withdrawn from exposure to lead.
Perverted sensations of the parts about to be affected, such as coldness, numbness, and hyperæsthenia, may precede the attack. Impairment of motor-power, manifested by feebleness, stiffness, or awkwardness and tremor, also appears in the prodromic period. This trembling consists in slight agitation of the muscles, rather than in well-marked rhythmical contractions. These precursors may indeed constitute the attack, which occasionally, and especially under treatment, terminates at this point. The prodromic symptoms are less severe during the day, while the patient is at work; at night they are aggravated. After some days they end in the characteristic paralysis. Colic is a common precursor. After the attack some stiffness of the muscles is experienced, which terminates by rapid loss of power or abruptly in actual palsy. Occasionally encephalopathy precedes the paralysis. It is rare that prodromes are wholly absent.
In the great majority of the cases the upper extremities and the extensor muscles are first attacked. If the paralysis be slight other muscles may escape. The characteristic form of lead paralysis consists in loss of power in the extensors of the hands and fingers, especially of the extensor communis, without implication of the supinator longus. The muscles affected are in the region of distribution of the musculo-spinal nerve. The deformity is known as wrist-drop. Next in order, the triceps and deltoid are most frequently attacked. The lower extremities commonly escape for a considerable time. When attacked, the extensor muscles of the feet and toes are the first to suffer.
Paralysis of the dorsal muscles occurs in rare instances. It gives rise to a peculiar stooping, uncertain, and tottering gait. Paralysis of the intercostal and laryngeal muscles was observed by Tanquerel. Paralysis of the muscles of the face or of those of the eye has never been observed in consequence of lead-poisoning. The loss of power never corresponds strictly to the distribution of the branches of a single nerve-track.
The paralysis, as a rule, affects both sides, and frequently the corresponding muscles of the two extremities. Sometimes, however, the affected muscles of the two sides are not the same, and it occasionally happens that the affection is limited to one side. In very rare cases, the arm and leg on the same side being paralyzed, the affection resembles hemiplegia.
Local paralysis may be limited to the extensor muscle of a single finger or may involve all the muscles of a limb. There may be slight impairment of power in the flexor muscles. The enfeeblement of certain flexor muscles, especially of those of the fingers, may, Naunyn suggests, be only apparent, the position of the hands being in pure extensor paralysis unfavorable to the exercise of the flexors and limiting their function.