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Nine L-dopa na ve patients with clinically diagnosed parkinsonism were studied using positron emission tomography with 6-L-18Ffluorodopa (18Fdopa, a pre-synaptic tracer) and 11Craclopride (which binds to D2 receptors). Putamen 18Fdopa uptake was reduced in all patients, confirming a loss of function affecting the nigrostriatal projection. In eight patients the putamen with the lowest 18Fdopa uptake (always contralateral to the clinically most affected side) had the highest 11Craclopride binding, suggesting upregulation of the post-synaptic D2 receptors. In the ninth patient 11Craclopride binding was lower in the putamen with the lowest 18Fdopa uptake, indicating an additional post-synaptic deficit. All nine patients were shown to be L-dopa responsive. The subsequent clinical course of the former eight patients has been typical of idiopathic Parkinson's disease, whilst the ninth patient has developed postural hypotension, urinary incontinence and respiratory stridor typical of multiple system atrophy. Reduced 11Craclopride binding in L-dopa naïve parkinsonian patients might serve as a useful early marker of this condition.
Sawle et al. (Fri,) studied this question.