Differences in nigro-striatal impairment in clinical variants of early Parkinson's disease: evidence from a FP-CIT SPECT study

INTRODUCTION: In idiopathic Parkinson's disease (PD), two different clinical phenotypes are usually distinguished: a tremor dominant variant (TD) and an akinetic-rigid type (ART). TD patients are characterized by a slower disease progression and a minor cognitive impairment. Striatal density of DAT, as quantified by FP-CIT SPECT, has been reported to correlate with rigidity and akinesia but not with tremor. OBJECTIVE: To evaluate FP-CIT uptake in TD and ART phenotypes. METHODS: We retrospectively evaluated from our database the pre-synaptic nigro-striatal function of 24 patients with TD-PD and 38 patients with ART-PD who underwent a FP-CIT SPECT within 1 year from disease onset. RESULTS: Disease duration, age at the time of SPECT scan and disease severity as measured with Unified Parkinson's Disease Rating scale part III (UPDRS III) were not statistically different between the two groups. Putamen contralateral to the most clinically affected side showed a lower FP-CIT uptake in ART patients compared to TD patients. No statistically significant differences emerged when considering bilateral caudate and ipsilateral putaminal uptake, as well as asymmetry indices and caudate/putamen ratios. FP-CIT contralateral putaminal uptake correlated with the severity of rigidity and hypokinesia but not with tremor. CONCLUSIONS: These data suggest that other neurotransmitter systems apart from the nigro-striatal dopaminergic system are involved in the generation of Parkinsonian tremor, and they are consistent with previous evidence of a lack of correlation between tremor severity and FP-CIT uptake. Putaminal relative sparing in TD patients could partially explain the slower disease progression reported in this PD phenotype