Clinical significance of striatal DOPA decarboxylase activity in Parkinson's disease.
We performed dynamic PET studies with fluorodopa (FDOPA) in 9 normal volunteers and 16 patients with Parkinson's disease to investigate the applicability of dopa decarboxylase (DDC) activity measurements as useful markers of the parkinsonian disease process.


METHODS
From the 3-O-methyl-FDOPA (3OMFD)/PET studies, we obtained mean population values of the kinetic rate constants for 3OMFD (K1M = 0.0400 and k2M = 0.0420). We applied these values to calculate striatal DDC activity using the FDOPA compartmental model. We estimated k3D in this group using dynamic FDOPA-PET and population mean K1M and k2M values. We then applied the mean population K1M and k2M values to estimate k3D(pop) to a new group (6 normal volunteers and 11 patients) studied only with dynamic FDOPA-PET. In all FDOPA/PET studies, we calculated striatal uptake rate constants (KiFD) using a graphical method and also measured the striato-occipital ratio (SOR).


RESULTS
Although DDC activity has been postulated as a precise indicator of presynaptic nigrostriatal dopaminergic function, KiFD and SOR provided better between-group discrimination than did estimates of striatal DDC activity. KiFD and k3D(pop) both correlated significantly with quantitative disease severity ratings, with a similar degree of accuracy (r = 0.69 and 0.63 for k3D(pop) and KiFD, respectively; p < 0.01).


CONCLUSIONS
Although estimated striatal DDC activity correlates with clinical disability, this measure is comparably less effective for early diagnosis. We conclude that a simple estimate such as striatal KiFD is superior to k3D measurements for most clinical and research applications.
Ishikawa
T
T
Department of Neurology, North Shore University Hospital/Cornell University Medical College, Manhasset, New York 11030, USA.
Dhawan
V
V
Chaly
T
T
Margouleff
C
C
Robeson
W
W
Dahl
J R
JR
Mandel
F
F
Spetsieris
P
P
Eidelberg
D
D
D001921:Brain / Q000000981:diagnostic imaging / Q000201:enzymology; D016022:Case-Control Studies; D003342:Corpus Striatum / Q000201:enzymology*; D004295:Dihydroxyphenylalanine / Q000031:analogs & derivatives* / Q000493:pharmacokinetics; D004296:Dopa Decarboxylase / Q000378:metabolism*; D005260:Female; D005462:Fluorine Radioisotopes; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D010300:Parkinson Disease / Q000000981:diagnostic imaging* / Q000201:enzymology*; D014055:Tomography, Emission-Computed / Q000379:methods*
D005462:Fluorine Radioisotopes; C055151:3-O-methyl-6-fluoro-dopa; C043437:fluorodopa F 18; D004295:Dihydroxyphenylalanine; D004296:Dopa Decarboxylase