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123I-IPT brain SPECT study in essential tremor and Parkinson’s disease

Objective: To investigate nigral neuronal damage in patients with isolated postural tremor and those with postural and rest tremor without parkinsonism. Methods: Using [123I]-N-(3-iodopropen-2-yl)-2β-carbomethoxy-3β-(4-chlorophenyl) tropane SPECT, we measured the basal ganglia-occipital cortex/occipital cortex ([BG-OCC]/OCC) uptake ratios in 21 control subjects and patients with isolated postural tremor (n = 9), postural and rest tremor (n = 6), and PD (n = 11). Results: In the patients with PD, the means (±SD) of the (BG-OCC)/OCC ratios of the ipsilateral (2.35 ± 0.37) and the contralateral (1.97 ± 0.33) sides to the more severely affected limbs were significantly lower than the mean of the bilateral (BG-OCC)/OCC ratios of the age-matched control subjects (3.83 ± 0.66). The mean (±SD) of the bilateral (BG-OCC)/OCC ratios of the patients with isolated postural tremor (3.60 ± 0.83) was comparable with that of the age-matched control subjects. However, the mean (±SD) of the bilateral (BG-OCC)/OCC ratios of the patients with postural and rest tremor (2.61 ± 0.18) was lower than that of the control subjects (p < 0.05). The mean of the bilateral (BG-OCC)/OCC ratios of the patients with postural and rest tremor was comparable with that of the side ipsilateral to the severely affected limbs of the patients with PD. However, it was higher than that of the side contralateral to the limbs more severely affected by PD. Four of the six patients with postural and rest tremor had (BG-OCC)/OCC ratios lower than 2 standard deviations from the mean of the age-matched control subjects. Conclusions: Later in their clinical courses, some patients with postural tremor may acquire rest tremor in association with mild substantia nigra neuronal loss.