Nervous system degeneration produced by acrylamide monomer.

Abstract

Acrylamide, widely employed as a vinyl monomer in the polymer industry, is a potent neurotoxin to man and to animals. The cumulative effect of prolonged, low-level exposure to acrylamide monomer is the insidious development of a progressive peripheral neuropathy. Sensory symptoms begin in the hands and feet (numbness, pins and needles), certain reflexes are lost and, with severe exposure, muscle weakness and atrophy occur in the extremities. The peripheral neuropathy may be supplemented by symptoms indicative of central nervous system damage (ataxia, tremor, somnolence and mental changes). The neuropathologic basis for this clinical picture has been determined in cats. Here, chronic acrylamide intoxication produces selective peripheral and central nerve fiber degeneration. Degeneration first occurs in the extremities of long and large nerve fibers which later undergo a progressive, seriate proximal axonal degeneration known as dying-back. Especially vulnerable are sensory axons supplying Pacinian corpuscles and muscle spindles in the hindfoot toepads, while adjacent motor nerve axons die back later. Distal central nerve fiber degeneration is seen in the medulla and the cerebellum. The neurotoxic property of acrylamide is of practical concern in two areas. One major problem is the protection of factory workers engaged in the manufacture of acrylamide. A sensitive test of neurologic function in these individuals, i.e., touch sensation, based on the experimental observation of the exquisite vulnerability of Pacinian corpuscles in acrylamide intoxicated cats, is presently under consideration. The second area for concern is the exposure of the populace to minute amounts of neurotoxic acrylamide monomer which contaminate acrylamide polymers currently deployed in the environment. Federal restrictions on the maximum permitted exposure to acrylamide, based on a largely clinical study of acrylamide neurotoxicity conducted ten years ago, may require a re-evaluation in the light of recent advances which have pinpointed the initial sites of nerve fiber degeneration.