Dopa‐responsive dystonia: [18F]dopa positron emission tomography

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Abstract
The syndrome of dopa‐responsive dystonia comprises a minority of patients with dystonia, yet it is of considerable diagnostic importance because patients respond dramatically to L‐dopa therapy. Benefits from this treatment are lasting, and the problems associated with long‐term L‐dopa therapy in patients with Parkinson's disease are generally absent. It has been suggested that this condition is due to a defect in the dopamine synthetic pathway, which is bypassed when patients are treated with L‐dopa. We have studied [18F]dopa uptake in 6 patients with classic doparesponsive dystonia (5 familial patients and 1 sporadic patient), aged 18 to 66 years. Data have been analyzed according to a graphic approach, calculating an influx constant for each region studied. We have also studied a seventh, clinically atypical, patient with juvenile dystonia‐parkinsonism. Similar data have been calculated for a group of 10 healthy control subjects and 10 patients with Parkinson's disease. The 6 patients with typical dopa‐responsive dystonia had a modest but significant reduction in the uptake of tracer into both caudate and putamen, which indicates a defect in the decarboxylation, vesicular uptake, and storage of [18F]dopa. This argues against the proposition that doparesponsive dystonia is due to an inherited defect of tyrosine hydroxylase alone. In the atypical patient, however, we found a greater reduction of [18F]dopa uptake into both caudate and putamen, comparable with that in patients with Parkinson's disease.