Amyotrophic lateral sclerosis in a battery-factory worker exposed to cadmium

A 44-year-old patient died from amyotrophic lateral sclerosis (ALS) after nine years of heavy exposure to cadmium (Cd) in a nickel-cadmium (Ni-Cd) battery factory. Two years after starting work he and co-workers had experienced pruritus, loss of smell, nasal congestion, nosebleeds, cough, shortness of breath, severe headaches, bone pain, and proteinuria. Upper back pain and muscle weakness progressed to flaccid paralysis. EMG findings were consistent with motor neuron disease. Cd impairs the blood-brain barrier, reduces levels of brain copper-zinc (Cu-Zn) superoxide dismutase (SOD), and enhances excitoxicity of glutamate via up-regulation of glutamate dehydrogenase and down-regulation of glutamate uptake in glial cells. High levels of methallothionein, a sign of exposure to heavy metals, have been found in brain tissue of deceased ALS patients. The effects of Cd on enzyme systems that mediate neurotoxicity and motor neuron disease suggest a cause-effect relationship between Cd and ALS in this worker.