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Abstract
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In mid-August 1973, a 43-year-old male employee of a plant producing vinyl-coated cloth presented to the neurosurgery service of the Ohio State University Hospital complaining of having been weak since May. On neurologic examination he was found to have bilateral weakness of the wrist extensors, wrist flexors, finger ex tensors, finger flexors, and finger abductors. He also had foot drop, absent ankle deep tendon reflexes, and atrophy of the interosseous muscles bilaterally. Electromyography confirmed the diagnosis of a relatively acute peripheral neuropathy. No etiology was determined. The patient revealed that 5 other employees in his department at the factory (the print department) had a similar illness. Four had been hospitalized, and 1 had been treated as an outpatient. These cases were reported to the Division of Occupational Health, Ohio Department of Health.
Suspecting that a toxic agent might be present in the plant, health officials performed electromyograms (EMG) on 1,156 employees. Those with abnormal EMGs were given a neurologic examination and were interviewed about previous neurologic disease. A total of 45 employees were found to have symptoms, signs, and EMGs consistent with an acute peripheral neuropathy not attributable to a known cause. Epidemiologic investigation revealed that 35 of the 45 employees worked in the print department where a mixture of methyl ethyl ketone and methyl butyl ketone (MBK) was used in large quantities as a solvent. This material was used less frequently and in much smaller quantities in other areas of the plant. MBK was first used in August 1972 and was put into full use by December 1972. As no other changes in materials had occurred in the past several years, MBK was implicated as the toxic agent. Furthermore, workers in an almost identical coated fabric factory in California in which MBK was not used had no disease.
Measurements of organic solvents in the print department atmosphere revealed several instances where vapor concentrations exceeded OSHA (Occupational Safety and Health Administration) standards. Printing machine operators, who had the highest attack rate as a group, were exposed to the highest concentrations of solvent vapors. In addition, they had significant exposure through other routes. Work practices and lack of protective clothing may have resulted in excessive skin exposure. Employees eating on the job demonstrated a significantly greater risk of acquiring the disease than those who did not. Finally, the affected employees worked significantly more overtime than nonaffected employees. The affected department was closed for I month in early September 1973. MBK was removed from production materials, improved ventilation was installed, and improved working practices were instituted.
Since the department's reopening in early October, no new cases of peripheral neuropathy have been discovered. The National Institute of Occupational Safety and Health is investigating the use of MBK in other areas of the country.
Editorial Note Neither MBK nor any of the other agents used in the plant have previously been associated with such an illness. Despite the use of a large variety of chemical compounds making it difficult to single out MBK as the sole toxic agent, no other agent appeared responsible. Animal experiments currently in progress may confirm MBK's neurotoxicity. Even without unequivocal identification of an agent, the outbreak illustrates the potential hazards of industrial sol- vents. MBK has come into widespread industrial use only in the past 2 or 3 years. As with many industrial solvents, only effects of acute exposure were investigated for the establishment of safety standards. In this outbreak, significant effects cr a chronic exposure were noted from a solvent which was thought to be safe. Furthermore, workers were exposed to large amounts of MBK by inadequate ventilation and genera! lack of appreciation for established safety procedures for working with organic solvents. Even if another agent had been involved, the outbreak terminated with the institution of proper ventilation and safe work practices. |