Different patterns of nigrostriatal degeneration in tremor type versus the akinetic-rigid and mixed types of Parkinson's disease at the early stages: molecular imaging with 123I-FP-CIT SPECT

The various associations of motor and non-motor symptoms, the onset of motor complications, the cognitive disorder's appearance and other factors make Parkinson's disease (PD) a heterogeneous syndrome with multiple phenotypes. The necessity of discriminating between different forms of PD could have a role in understanding the pathophysiology of extrapyramidal signs with clinical implications. The aim of this study was to evaluate if there is a relationship between the clinical motor phenotypes of PD and the scintigraphic pattern of 123I-FP-CIT single photon emission computed tomography (SPECT). We examined 47 patients with early idiopathic PD (25 males; 22 females; mean age 58±2 years) and subdivided them in different clinical forms on the basis of dominance of resting tremor (n=20), bradykinesia plus rigidity (n=20) and the presence of both clinical signs [mixed type (MT, n=7)]. We correlated this status with the semi-quantitative analysis of SPECT with 123I-FP-CIT. Tremor type patients showed a lower reduction of 123I-FP-CIT uptake compared to akinetic-rigid type patients in contralateral caudate (P=0.0139) and putamen (P=0.0028) nuclei. 123I-FP-CIT uptake was higher in the ipsilateral caudate (P=0.0050) and putamen (P=0.0012) of tremor type patients compared to akinetic-rigid type patients. Comparisons of the striatal uptake in the tremor type and akinetic-rigid type patients with the MT patients revealed significant differences only in the ipsilateral and contralateral caudate. Our data indicate that in akinetic-rigid patients the dopaminergic system is more involved compared to that in the tremor type patients and that this difference is present from the initial stage of the disease. Moreover, our results suggest that PD phenotypes could be related not only to the dopaminergic involvement but also to other systems.