There are several case reports of parkinsonism in humans following solvent exposures. A patient who abused lacquer thinner developed acute onset of asymmetric parkinsonism with levodopa responsiveness, but normal positron emission tomography (PET) with 6-[18F] fluorodopa ([18F]FDOPA PET) uptake (38). A patient exposed to occupational n-hexane also developed asymmetric parkinsonism with levodopa responsiveness, but reduced [18F]FDOPA PET uptake (62). A patient with mixed solvent exposures from petroleum waste developed transient parkinsonism associated with transient reduction in [18F]FDOPA PET uptake, suggesting that there may be a critical duration of exposure beyond which the symptoms are irreversible (63).
Although normal [18F]FDOPA PET implies that the etiology of a patient's parkinsonism is not likely idiopathic PD, we do not know the sensitivity and specificity of [18F]FDOPA PET for idiopathic PD. In case reports, it is difficult to elucidate causation from incidental, sporadic PD. A case-control study of 188 PD subjects drawn from a cohort study of occupational hydrocarbon exposures found that exposed subjects had a significantly earlier age of disease onset than PD controls, suggesting that hydrocarbons are an environmental accelerant (64). A follow-up study with more detailed dose reconstruction is needed to confirm these findings, as solvents are potentially an important risk factor for PD.
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