Progression after chronic manganese exposure.

We report a longitudinal follow-up study on six patients with chronic manganese-induced parkinsonism following cessation of manganese exposure. Compared with the 1987 study, their parkinsonian symptoms showed a slow progression, particularly in gait disturbances such as freezing during turning and walking backward with retropulsion. The mean disability scores on the King's College Hospital Rating Scale were 15.0 +/- 4.2 in 1987 and 28.3 +/- 6.7 in 1991 (p = 0.003, paired t test). Review of the video records also confirmed a worsening of parkinsonism, especially in difficulty turning. Three of six patients receiving levodopa treatment had an initial improvement. The response decreased after 2 to 3 years. During the therapy, they did not develop on-off fluctuation or dyskinesia. We conclude that patients with manganese-induced parkinsonism may develop increasing neurologic dysfunction long after cessation of exposure and that their responses to levodopa are different from those of patients with Parkinson's disease.