Does diisocyanate exposure result in neurotoxicity?

CONTEXT

Diisocyanates have been associated with respiratory and dermal sensitization. Limited number of case reports, and a few case studies, media, and other references suggest potential neurotoxic effects from exposures to toluene diisocyanate (TDI), 1,6 hexamethylene diisocyanate (HDI), and methylene diisocyanate (MDI). However, a systematic review of the literature evaluating the causal association on humans does not exist to support this alleged association.

OBJECTIVE

To perform systematic review examining the body of epidemiologic evidence and provide assessment of causal association based on principles of the Sir Austin Bradford Hill criteria or considerations for causal analysis.

METHODS

A comprehensive search of public databases for published abstracts, case reports, cross-sectional surveys, and cohort studies using key search terms was conducted. Additional searches included regulatory reviews, EU IUCLID and EU Risk Assessment databases, and unpublished reports in the International Isocyanate Institute database. An expert panel consisting of physicians, toxicologists, and an epidemiologist critically reviewed accepted papers, providing examination of epidemiologic evidence of each report. Finally, the Hill criteria for causation were applied to the summative analysis of identified reports to estimate probability of causal association.

RESULTS

Twelve papers reporting exposed populations with a variety of neurological symptoms or findings suitable for analysis were identified, including eleven case or case series reports, and one cross-sectional study. Three papers reported on the same population. Each of the papers was limited by paucity of diisocyanate exposure estimates, the presence of confounding exposures to known or suspected neurotoxicants, a lack of objective biological measures of exposure or neurotoxic effects, and lack of relative strength of association measures. Additionally, reported health symptoms and syndromes lacked consistency or specificity. No plausible mechanism of toxicity was found. Application of a predictive mathematical model for determining probability of causal association for neurotoxicity was calculated to be 21%.

CONCLUSION

There is insufficient evidence for a causal association of neurotoxic effects and diisocyanate exposure based on lack of evidence in all categories of the Hill criteria for causality except for temporal association of reported symptoms and alleged exposure. Future reports should attempt to address more rigorous exposure assessment and control for confounding exposures.

Risk factors for violent behavior among incarcerated male psychiatric patients: a multimethod approach

A multimethod approach that included demographic, criminal offense, drug use, neuropsychological, Rorschach, psychiatric diagnosis, and psychopathy characteristics was used to evaluate 131 incarcerated male psychiatric inpatients. Each criminal offense was ranked from nonviolent to severely violent, and participants were classified as having lifetime histories of either high or low violent behavior. Univariate analyses revealed 12 characteristics which independently discriminated inmates with lifetime histories of high or low violent behavior (married, non-Caucasian race, Axis I psychotic diagnosis, drug other than alcohol or marijuana used most, positive for psychopathy on the Hare Psychopathy Checklist Revised, scores indicating impairment on the Halstead Impairment Index and Category Test, and five Rorschach measures). Logistic regression revealed that eight of those characteristics (married, non-Caucasian race, Axis I psychotic diagnosis, positive for psychopathy on the Hare Psychopathy Checklist Revised, scores indicating impairment on the Halstead Impairment Index, and Rorschach Coping Deficit Index, Personal Responses, and Raw Sum Special Scores) significantly contributed to identifying inmates with lifetime histories of highly violent behavior. Data are provided for sensitivity, specificity, positive and negative predictive power, and overall correct classification rate for neuropsychological and Rorschach measures. Because this sample represented only incarcerated male psychiatric inpatients, and not a general prison population, caution as to limits of generalization are discussed. Implications for use of this information in understanding violent behavior are also discussed.

Neuropsychological toxicology of methylene diphenyl diisocyanate: a report of five cases

The neuropsychological functioning of five men suffering alleged physical, cognitive and behavioural changes following exposure to methylene diphenyl diisocyanate (MDI), an industrial chemical, was investigated in the present study. At the time of assessment, four of the five patients remained symptomatic despite having no contact with MDI for periods ranging from 5 to 9 months. All patients reported experiencing subjective symptoms consisting of respiratory distress, headaches, depression, irritability, forgetfulness, decreased calculating ability, word-finding problems and reduced concentration. While the pattern of neuropsychological deficits varied among the patients, common findings for the group included intact psychomotor, psychosensory, visuographic and language functions accompanied by deceased concentration, mental efficiency, rate of information processing, learning ability and abstract reasoning. All five patients also revealed significant emotional distress on an objective personality measure. In general, the neuropsychological test data support the presence of behavioural and cognitive correlates of CNS injury following exposure to MDI.