To the Editor:
A syndrome of solvent neurotoxicity or organic solvent syndrome has been widely described, in which individuals chronically and sometimes acutely exposed to organic solvent mixtures develop symptoms of cognitive dysfunction, fatigue, headache, and difficulties with memory and concentration. In these patients, cognitive disabilities wax and wane with exposures Citation[1] and correlate with present but not cumulative exposures to solvents Citation[2]. Neuropsychiatric testing has been used to document abnormalities.
Rosenberg and collaborators have recently reported in this journal that solvent abusers and other substance abusers have abnormalities on neuropsychological testing and MRI scan. “Attempts to estimate a dose-response relationship” found that MRI findings but not neuropsychological test results had a dose-response relationship. These authors concluded “reliance upon these [neuropsychological] tests in assessing injury from solvents is a highly dubious practice” Citation[3].
That no dose-response relationship was found for neuropsychiatric test result in solvent abusers does not make their use a dubious practice. Difficulty with memory and cognition are often the initial subjective complaints associated with neurotoxins, including solvents. Some believe that present neuropsychological testing is the accepted method to evaluate those complaints, a practice challenged by Rosenberg et al.
Morrow and collaborators demonstrated that recent exposure greatly affected impairments of learning and memory in solvent-exposed workers Citation[1]. Chouareire and collaborators found deficits in workers exposed to toluene correlated with present exposure but not cumulative exposure to toluene Citation[2]. Longitudinal studies of solvent exposed workers who had not developed neurocognitive complaints reported subclinical deficits but, similar to the findings of Rosenberg et al., no dose-response relationships at the doses observed Citation[3]Citation[4]Citation[5]. Some have hypothesized that there may be a group of individuals who are unusually susceptible to chemical effects, such as from solvent exposure. Although such populations have not been scientifically demonstrated, we should not totally dismiss the possibility of their existence. If such a population does exist, then neuropsychological testing data may be valid even if a dose-response relationship has not been demonstrated.
In summary, not all measurements of impairment from exposure demonstrate dose-response relationship, as is the case for neuropsychiatric testing to measure cognitive impairment from solvent exposures. Another example is pulmonary function tests to measure impairment in occupational asthma. Results wax and wane with exposures, are not grossly abnormal in those who have not developed the disease, and susceptible groups are known to exist.
William J. Meggs, M.D., Ph.D. F.A.C.E.P., F.A.C.M.T.
Division of ToxicologyDepartment of Emergency Medicine
Brody School of Medicine at East Carolina University Greenville, North Carolina 27858, USA
Fax: 252-816-3589;
References
- Morrow LA, Steinhauer SR, Condray R, Hodgson M. Neuropsychological performance of journeymen painters under acute solvent exposure and exposure-free conditions. J Int Neuropsychol Soc 1997; 3(3)269–275
- Chouaniere D, Wild P, Fontana JM, Hery M, Fournier M, Baudin V, Subra I, Rousselle D, Toamain JP, Saurin S, Ardiot MR. Neurobehavioral disturbances arising from occupational toluene exposure. Am J Ind Med 2002; 41: 77–88
- Rosenberg NL, Grigsby J, Dreisbach J, Busenbanrk D, Grigsby P. Neuropsychologic impairement and MRI abnormalities associated with chronic solvent abuse. Clin Toxicol 2002; 40: 21–34
- Bleecker ML, Bolla KL, Agnew J, et al. Dose-related subclinical neurobehavioral effects of chronic exposure to low levels of organic solvents. Am J Ind Med 1991; 19: 715
- Cherry N, Hutchins H, Pace T, et al. Neurobehavioral effects of repeated occupational exposure to toluene and paint solvents. Br J Ind Med 1985; 42: 291