SPECT study with I-123-Ioflupane (DaTSCAN) in patients with essential tremor. Is there any correlation with Parkinson's disease?

OBJECTIVES: The differential diagnosis between essential tremor (ET) and Parkinson's disease (PD) may be, in some cases, very difficult on clinical grounds alone. In addition, it is accepted that a small percentage of ET patients presenting symptoms and signs of possible PD may progress finally to a typical pattern of parkinsonism. Ioflupane, N-u-fluoropropyl-2a-carbomethoxy-3a-(4-iodophenyl) nortropane, also called FP-CIT, labelled with (123)I (commercially known as DaTSCAN) has been proven to be useful in the differential diagnosis between PD and ET and to confirm dopaminergic degeneration in patients with parkinsonism. The aim of this study is to identify dopaminergic degeneration in patients with PD and distinguish them from others with ET using semi-quantitative SPECT (123)I-Ioflupane (DaTSCAN) data in comparison with normal volunteers (NV), in addition with the respective ones of patients referred as suffering from ET, as well as, of patients with a PD diagnosis at an initial stage with a unilateral presentation of motor signs.
METHODS: Twenty-eight patients suffering from ET (10 males plus 18 females) and 28 NV (12 males and 16 females) were enroled in this study. In addition, 33 patients (11 males and 22 females) with an established diagnosis of PD with unilateral limb involvement (12 left hemi-body and 21 right hemi-body) were included for comparison with ET. We used DaTSCAN to obtain SPECT images and measure the radiopharmaceutical uptake in the striatum (S), as well as the caudate nucleus (CN) and putamen (P) in all individuals.
RESULTS: Qualitative (Visual) interpretation of the SPECT data did not find any difference in the uptake of the radiopharmaceutical at the level of the S, CN and P between NV and ET patients. Reduced accumulation of the radiopharmaceutical uptake was found in the P of all PD patients. Semiquantitative analysis revealed significant differences between NV and ET patients in the striatum, reduced in the latter. There was also a significant reduction in the tracer accumulation in the left putamen of patients with right hemi-parkinsonism compared to ET and NV. Patients with left hemi-parkinsonism, demonstrated reduced radioligand uptake in the right putamen in comparison with ET and NV. Clinical follow-up of 20 patients with ET at (so many months afterwards) revealed no significant change in clinical presentation, particularly no signs of PD. Follow-up DaTSCAN performed in 10 of them (so many months afterwards) was negative in all but one. This one had an equivocal baseline study which deteriorated 12 months later.
CONCLUSIONS: Our results do not support the hypothesis of a link between essential tremor and Parkinson's disease. However, it appears that ET patients have a small degree of striatal dopaminergic degeneration. If this is due to alterations in the nigrostriatl pathway or of other origin it is not clear. Follow-up studies of essential tremor patients are warranted to assess progression of disease and to understand better the possible cause for striatal dopaminergic degeneration.