Detection of response to COMT inhibition in FDOPA PET in advanced Parkinson's disease requires prolonged imaging

The aim was to investigate whether the improved 6-[F-18]fluoro-L-dopa (FDOP A) availability induced by catechol-O-methyltransferase (COMT) inhibition c an be more clearly seen during late than during standard (early) imaging in FDOPA uptake in Parkinson's disease (PD) patients with severe dopaminergic hypofunction. Six PD patients and six healthy controls were investigated u p to 3.5 h after FDOPA injection with and without a single 400-mg dose of a peripheral COMT inhibitor, entacapone. Prolonged (late) imaging showed a s ignificantly higher increase in FDOPA uptake than standard 1.5 h (early) im aging after entacapone both in controls and in PD patients. The increase in the (putamen-occipital):occipital ratios was 37.4% during early and 70.4% during late imaging in controls. In PD patients, there was no significant c hange in the ratios during early imaging, but the late imaging showed a sig nificant increase in the putamen-to-occipital ratio of 54.2% after COMT inh ibition. Late imaging reveals more clearly the prolonged FDOPA availability induced by COMT inhibition leading to higher cumulated striatal activity c ompared with early imaging. This might be worth considering in FDOPA studie s, especially if investigations are planned to do without blood sampling. L ate imaging shows the storing potential of FDA better than is seen during e arly FDOPA PET imaging after entacapone administration. In patients with se vere presynaptic dopaminergic hypofunction, its detection requires prolonge d imaging. (C) 2001 Wiley-Liss, Inc.