Loss of dopamine transporter binding in Parkinson's disease follows a single exponential rather than linear decline.
Imaging of L-dopa uptake or dopamine transporter binding can monitor the progression of Parkinson's disease. Most follow-up studies have provided data best fitted by a linear decline of their outcome measure. However, in these studies, patients were repeatedly scanned during their first years after a diagnosis had been established.


METHODS
We followed 6 patients with early Parkinson's disease for 7.5 y using 123I-labeled N-(3-iodopropene-2-yl)-2beta-carbomethoxy-3beta-(4-chlorophenyl) tropane and SPECT.


RESULTS
Loss of dopamine transporter binding was best fitted using a single exponential approximation. A 63% loss (tau [time constant tau]) was calculated as 5.18 +/- 7.62 y in the putamen and 10.62 +/- 31.4 y in the caudate nucleus when a 3-parameter fit was used.


CONCLUSIONS
These data approximate, for what is to our knowledge the first time, the decline of dopamine transporter binding as expected in biologic systems and may allow for models that correct for exponential decline to be developed and for disease-modifying effects in patients with advanced disease to be determined.
Schwarz
Johannes
J
Department of Neurology, University of Leipzig, Leipzig, Germany. johannes@caltech.edu
Storch
Alexander
A
Koch
Walter
W
Pogarell
Oliver
O
Radau
Perry E
PE
Tatsch
Klaus
K
D001921:Brain / Q000000981:diagnostic imaging / Q000378:metabolism; D003198:Computer Simulation; D018450:Disease Progression; D050483:Dopamine Plasma Membrane Transport Proteins; D005500:Follow-Up Studies; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods; D007700:Kinetics; D016014:Linear Models; D008137:Longitudinal Studies; D008562:Membrane Glycoproteins / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000378:metabolism*; D008657:Metabolic Clearance Rate; D008954:Models, Biological; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D017711:Nonlinear Dynamics; D009662:Nortropanes / Q000493:pharmacokinetics*; D010300:Parkinson Disease / Q000000981:diagnostic imaging* / Q000378:metabolism*; D011485:Protein Binding; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics; D012720:Severity of Illness Index; D014018:Tissue Distribution; D015899:Tomography, Emission-Computed, Single-Photon / Q000379:methods
D050483:Dopamine Plasma Membrane Transport Proteins; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; C113010:N-(3-iodoprop-2-enyl)-2-beta-carbomethoxy-3-(4-methylphenyl)nortropane; D009419:Nerve Tissue Proteins; D009662:Nortropanes; D019275:Radiopharmaceuticals