A case of amyotrophic lateral sclerosis in electronic parts manufacturing worker exposed to lead

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease affecting the motor neurons of the spinal cord and brain. Although the definite etiology of ALS remains unclear, occupational or environmental exposures have been considered as one of the potential causes of ALS. Here, we report the case of a patient with ALS who used to work in a factory manufacturing electronic parts and has evidence of acute exposure to lead in excess.A 39-year-old man visited a neurology clinic with symptoms of progressive limb weakness and spasticity, which began 2 years ago. Upon neurological examination, symptoms of atrophy, spasticity and fasciculation of the lower extremities were evident. There were no signs of impairment of the cranial nerves, and cognitive and sensory functions were normal. Complete blood counts, blood chemistries and urinalysis were normal. Serial electromyography showed progressive denervative changes, which were consistent with motor neuron diseases. ALS was diagnosed according to the standard of the “Diagnostic criteria of the World Federation of Neurology”.The patient was handling lead oxide (PbO) for development of positive temperature coefficient (PTC) thermist, without being provided with proper respiratory protective equipment.Blood lead level of the patient was measured at 30.86 μg/dL 6 months after he quit his job. Bone lead levels from X-ray fluorescence (XRF) were below the normal range (3 ppm). Blood lead level of his co-workers at the same workplace were above the ACGIH recommended biological exposure index (BEI: 30 μg/dL). We speculated that the ALS in this case was related to excessive exposure to lead.