[123I]-FP-CIT-SPECT demonstrates dopaminergic deficit in orthostatic tremor

There is increasing evidence of a potential role of the dopaminergic system in orthostatic tremor (OT): Association with parkinsonism and treatment effects of L‐dopa and dopamine agonists have been reported. Eleven patients with isolated OT had single‐photon emission computed tomography (SPECT) using 123I‐FP‐CIT ([123I]‐2β‐carbomethoxy‐3β‐(‐4‐iodophenyl)‐N‐(3‐fluoropropyl)‐nortropane) as dopamine transporter tracer. Results were compared with 12 age‐matched normal controls and 12 patients with Parkinson's disease (PD). A marked reduction in striatal tracer binding was found in OT compared to normal controls (p < 0.001). Tracer uptake was significantly higher and more symmetrical than in PD, and caudate and putamen were equally affected. L‐dopa challenges, performed in seven patients, showed a small but non‐significant improvement on EMG and a small but significant improvement in clinical parameters on blinded video rating. Two‐month open‐label L‐dopa treatment (600 mg/day) led to a small improvement in two of five patients but no significant overall change. Olfactory function on University of Pennsylvania Smell Identification Test was normal. Our finding of a marked tracer uptake reduction on dopamine transporter SPECT supports a role of the dopaminergic system in OT. Lack of evidence of a clinically relevant therapeutic response to L‐dopa suggests that other mechanisms must also be involved in the pathogenesis. Ann Neurol 2003