Rigidity decreases resting tremor intensity in Parkinson's disease: A [I-123]beta-CIT SPECT study in early, nonmedicated patients

Tremor is one of the clinical hallmarks of Parkinson's disease (PD). Althou gh it is accepted that other classic symptoms of PD such as rigidity and br adykinesia result from a degeneration of the nigrostriatal system and subse quent reduction in striatal dopamine, the pathophysiology of resting tremor remains unclear. The majority of recent single photon emission computed to mography (SPECT) and positron emission tomography (PET) studies, using vari ous radioligands, demonstrated significant correlation between striatal rad ioligand bindings and the degree of parkinsonian symptoms such as rigidity and bradykinesia, but not tremor. We investigate the relationship between t he degeneration of the nigrostriatal pathway and the appearance of resting tremor, taking into account the possible interference of rigidity with the resting tremor. Thirty early and drug-naive PD patients were examined. Trem or and rigidity of the arms were assessed using UPDRS, and the power of tre mor was estimated using spectral analysis of tremor peaks. [I-123]beta -CIT SPECT was used to assess degeneration of the dopaminergic system in PD pat ients. A comparison between asymmetry indices showed that in terms of both tremor and rigidity, the most affected arm corresponded significantly with the contralateral striatum, having the largest reduction in radioligand bin ding. Furthermore, tremor power accounted for a significant part of varianc e in the contralateral striatum, suggesting a relationship between this PD symptom and the degeneration of the dopaminergic system. Further, the degre e of tremor was reduced with increasing rigidity. However, correcting for t he influence of rigidity, the significant contribution of tremor in the var iance in the contralateral striatal [I-123]beta -CIT binding disappeared. W hen the confounding influence of rigidity is taken into account, no signifi cant direct relationship between dopaminergic degeneration and the degree o f tremor could be found. Other pathophysiological mechanisms should be simi larly investigated in order to further our understanding of the origin of r esting tremor in PD. (C) 2001 Movement Disorder Society.