Semi-quantitative striatal-to-occipital ratios on l-3,4-dihydroxy-6-F-18 fluorophenylalanine brain positron emission tomography in idiopathic parkinson's disease

To evaluate striatal-to-occipital ratios (SOR) on L-3,4-dihydroxy-6-F-18 fluorophenylalanine (FDOPA) positron emission tomography (PET) in early and advanced idiopathic Parkinson's disease (IPD) based on clinical rating scales - unified Parkinson disease rating scale (UPDRS) and Hoehn and Yahr (H and Y) scale. Since an underlying serotonergic deficit is the pathophysiology in tremor predominant IPD, we derived midbrain-to-occipital ratio (MOR) on FDOPA PET in this subgroup. We evaluated a total of 20 IPD patients with FDOPA PET brain. Each patient underwent dopaminergic imaging after undergoing a detailed clinical examination at the movement disorder clinic of our institute. This included nine early IPD (UPDRS = 30.3 ± 5.6; range 19-36, H and Y < 2.0 and disease duration = 3.4 ± 0.9; range 2-5 years) and 11 advanced IPD (UPDRS = 54.3 ± 7.2; range 44-66 and H and Y = 2.0-4.0, disease duration = 6.6 ± 3.2; range 4-14 years). Twelve patients who had undergone FDOPA PET for reason other than Parkinsonism were included as control. Regions of interest were generated for the caudate, putamen, occipital regions, and midbrain on fused PET images for structural correlation. SORs were generated for caudate and putamen and MOR for midbrain. Statistical analysis using Mann-Whitney U-test was performed between controls to early and advanced IPD separately. MOR was compared between non-tremor dominant and tremor predominant IPD (assessed by UPDRS tremor score). SOR clearly differentiated between controls and early as well as advanced IPD (P = 0.006 and 0.003, respectively). SOR between early and advanced IPD patients was also significantly different (P = 0.018). Comparison between contralateral SOR (to predominant symptom sidedness) to ipsilateral SOR was significantly different in early IPD (P = 0.032) while no significant difference was noted for advanced IPD (P = 0.507). MOR in tremor predominant subgroup showed significant difference from non-tremor dominant subgroup group (P = 0.002). SOR is a good diagnostic tool for IPD patients and can differentiate between early and advanced IPD. SOR correlates well with clinical sidedness in early IPD but not in advanced IPD. MOR can be used in the tremor predominant patient subgroup when SORs may not be useful. (author)