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

Abstract

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 (123)I-FP-CIT ([(123)I]-2 beta-carbomethoxy-3beta-(-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.

Intact serotonergic and dopaminergic systems in two cases of orthostatic tremor

“…Whether in such OT cases the SERT function is also abnormal has to be investigated in further studies. While the role of dopaminergic dysfunction in the pathophysiology of OT remains controversial [2,3,7], our data suggest that the integrity of the serotonergic innervation is not affected in OT.…”

“…1 cd) suggesting intact presynaptic serotonergic pathways in these cases. However, in some OT patients the dysfunction of modulatory control of a higher motor centre (basal ganglia) associated with reduced striatal DAT availability could play a part in the pathophysi-ology [2]. Whether in such OT cases the SERT function is also abnormal has to be investigated in further studies.…”

“…A previous single-photon emission computed tomography (SPECT) study demonstrated striatal dopamine transporter (DAT) deficits in OT [2] but also patients with normal presynaptic nigrostriatal pathway have been reported [3]. OT has been suggested to arise from a central oscillator involving the brainstem or cerebellum [4][5][6][7].…”

Temblor ortostático como causa de inestabilidad postural en enfermedad de Parkinson: Caso clínico

“…El más frecuentemente descrito es el rápido, como en nuestra paciente, que además remeda el temblor ortostático primario (no asociado a otras enfermedades). Este tipo de temblor rápido tendría un origen independiente de la inervación dopaminérgica estriatal como ha sido demostrado por la ausencia de denervación dopaminérgica en estudios de radioligandos 15 y en los casos con denervación dopaminérgica ella sigue un patrón distinta de la observada en la EP 15,16 . El temblor ortostático rápido tiene pobre mejoría con levodopa y agonistas dopaminérgicos 17,18 , siendo su repuesta preferentemente al uso de clonazepam 4,19 .…”

Familial orthostatic tremor: An additional report in siblings

“…Although there is some evidence of a dopaminergic deficit, 4 the exact circuit responsible for the high frequency, 13-18 Hz tremor that is pathognomonic for this disorder remains unclear. OT is thought to be sporadic rather than familial, which makes the search for a pathophysiologic mechanism particularly challenging.…”