—The first muscle affected is the extensor communis digitorum, with dropping of middle and ring fingers, while extension of the first and fourth is possible because of their separate muscles of extension (extensor minimi digiti and extensor indicis). Paralysis may be limited to these, and not advance farther, but it is common to see these two muscles primarily affected, and for other muscles to become involved after the patient is put on treatment, although exposure to lead has ceased. Usually, however, the paralysis advances, involving the extensors of the index and little fingers, so that the basal phalanges of the four fingers cannot be extended. The long extensor of the thumb is next involved, but this may be delayed. The two terminal phalanges are still able to be extended by the interossei (as shown by Duchenne) when the basal phalanx is passively extended on the metacarpal. Abduction and adduction of the fingers also remain unaffected. The wrist muscles are affected next. The hand remains in semi-pronation, and when hanging down forms a right angle with the forearm, the fingers slightly flexed with the thumb towards the palm, and the hand deflected to the ulnar side. In grasping an object the flexors remain unaffected, the wrist is much flexed owing to the shortening of the flexors in consequence of the extensor paralysis. The hand cannot pass the median line. The long abductor of the thumb—that is, the extensor ossis metacarpi pollicis, also known as the “extensor primi internodii pollicis”—is only very rarely involved, but has been described as being the muscle alone involved in the paralysis affecting persons engaged in polishing lead capsules.
2. The Superior or Brachial Type (Remak).
—The muscles affected are those of the Duchenne-Erb group—namely, the deltoid, biceps, brachialis anticus, and supinator longus. The supra- and infrascapular muscles are also as a rule involved, but the pectoralis major rarely. This type of paralysis is usually found in old cases associated with other forms of paralysis, but may be found as a primary affection (as already noted amongst painters); sometimes the deltoid is the only muscle affected, with diminution in electrical contractility of the other muscles of the group.
The arm hangs loosely by the trunk, with the forearm semi-pronated. The arm cannot be raised, nor can the forearm be bent on the upper arm. Extension is unaffected, as the triceps is never involved. Supination is impossible because of paralysis of the supinator brevis. Movement effecting rotation of the shoulders is involved, due to the paralysis of the supra- and infra-spinatus. Electrical reactions are said to be less marked in the brachial than the antibrachial type, and complete loss of faradic contractility is rare; but in one of the three cases described below, in which electrical reactions were carefully tested, the right deltoid showed entire loss of contractility to faradism.
3. Aran-Duchenne Type.
—The muscles of the thenar and hypothenar eminences and interossei are affected. This type of lead paralysis may be distinguished from progressive muscular atrophy by the electrical reactions, and the fact that the atrophy is accompanied by more or less pronounced muscular paralysis. The atrophy is almost always most marked, and advances pari passu with the paralysis. This form may occur alone, or be complicated with the antibrachial type, which is the most common. It is seen in file-cutters as the result of overstrain of the muscles in question. Moebius[9], in his observations on file-cutters, noted in one case paralysis of the left thumb, with integrity of the other muscles of the left upper extremity. Opposition of the thumb was very defective; there was paralysis of the short flexor and of the adductor and atrophy of the internal half of the hypothenar eminence. Reaction of degeneration was noted in the muscles named, but not in the extensors of the fingers and wrist. In another case, in addition to feebleness of the deltoid, flexors of forearm on the upper arm, and small muscles of hand, there was paralysis and atrophy of the adductor of the thumb and first interosseous and paralysis of the opponens.
4. Peroneal Type.
—This is a rare type, and nearly always associated with the antibrachial or with generalized paralysis. In the former the paralysis is slight, especially when it affects the psoas; but there is predilection for certain groups of muscles, especially the peroneal and extensor of the toes, while the tibialis anticus escapes. Hyperæsthesia, or more rarely anæsthesia, precedes the onset.
The patient walks on the outside of the feet, has difficulty in climbing stairs, and cannot stand on the toes. The toes drag on the ground in walking, so that the foot has to be swung round at each step, and the inner side is lifted in excess by the action of the tibialis anticus, with uncertainty in gait. If walking is continued, the toes drag more, and “stepping” gait is assumed by bringing into action the muscles of the thigh. The foot cannot be flexed on the leg; abduction of the foot and extension of the basal phalanx of the toes is impossible. Later the peroneal muscles, extensor communis of toes, and extensor of great toe, are paralyzed, from which fact arises the difficulty of walking and of descending stairs, as the whole weight of the body is supported then by the tibialis anticus. This type corresponds with the antibrachial type of the upper extremity. If the tibialis anticus is paralyzed, it is in association with the gastrocnemius.