In a few of the chronic polyneuropathies, the feet, hands, and even the spine may become progressively deformed. This is most likely to occur when the disease begins during childhood. Austin pointed out that foot deformity is found in 30 percent of patients with hereditary polyneuropathy, and spine curvature is found in 20 percent. In early life, the feet are pulled into a position of talipes equinus (plantar deviation) because of disproportionate weakness of the pretibial and peroneal muscles and the unopposed action of the calf muscles. Weakness of the intrinsic foot muscles during the period of life when the bones are forming allows the long extensors of the toes to dorsiflex the proximal phalanges and the long flexors to shorten the foot, heighten the arch, and flex the distal phalanges. The result is the claw foot—le pied en griffe—or pes cavus (high arches) when the process is less severe. These changes in the structure of the foot are valuable diagnostic indicators that a neuromuscular disease originated in early childhood or during intrauterine development. A congenital claw hand has a similar implication. Unequal weakening of the paravertebral muscles on the 2 sides of the spine during early development leads to kyphoscoliosis.
Denervation atrophy of muscle can be considered the main trophic disturbance resulting from interruption of the motor nerves. However, there are numerous other changes. Analgesia of distal limb parts makes them susceptible to burns, pressure sores, and other forms of injury that are easily infected and heal poorly. In an anesthetic and immobile limb, the skin becomes tight and shiny, the nails curved and ridged, and the subcutaneous tissue thickened (“trophic changes”). Hair growth is diminished in denervated areas. If the autonomic fibers are also interrupted, the limb becomes warm and pink. Repeated injuries and chronic subcutaneous and osteomyelitic infections result in a painless loss of digits and the formation of plantar ulcers (mal perforant du pied). These are prominent features of the recessive form of hereditary sensory neuropathy and we have observed them in dominant forms as well. In tabes dorsalis and syringomyelia as well as certain familial and other chronic polyneuropathies, analgesic joints, when chronically traumatized, may first become deformed and then actually disintegrate in a process called Charcot arthropathy (“Charcot joint”).
Apart from analgesia, a critical factor in these trophic changes may be aberrant neural regulation of the distal vasculature, which interferes with normal tissue responses to trauma and infection. Ali and colleagues have related the ulcer formation to loss of C fibers, which mediate both pain and autonomic reflexes. However, paralyzed limbs, even in hysteria, if left dependent, are often cold, swollen, and pale or blue. These are probably secondary effects of immobilization, as pointed out long ago by Lewis and Pickering. Erythema and edema, burning pain, and cold sensations surely can be evoked by peripheral nerve irritation, particularly of C and A-δ fibers as discussed in Chap. 7.
Anhidrosis and orthostatic hypotension, two of the most frequent manifestations of autonomic failure, predominate in certain types of polyneuropathies. They occur frequently in amyloidosis and in other small-fiber polyneuropathies, especially diabetic, and in several congenital types. These are also the main features of an acute autonomic polyneuropathy called pandysautonomia (Young et al; Adams et al; Low et al) and can be prominent in some cases of GBS. The neuropathic dysautonomic conditions are described in detail in Chap. 25 and later in this chapter.