Dopaminergic deficit is not the rule in orthostatic tremor

Involvement of the dopaminergic system in orthostatic tremor is controversial. The aim of this study was to detect possible dopaminergic denervation in primary orthostatic tremor (OT). Twelve consecutive patients with a firm diagnosis of primary orthostatic tremor were compared with age-matched normal controls. All the patients had a neurological examination, surface polymyography, and quantification of striatal dopamine transporters with ¹²³I-FP-CIT SPECT imaging. There was no significant difference in ¹²³I-FP-CIT SPECT findings between controls and patients with OT. Longstanding primary orthostatic tremor is not necessarily associated with ¹²³I-FP-CIT SPECT abnormalities, as 8 of our patients had more than a 10-year history of OT. Primary orthostatic tremor without dopaminergic denervation remains a valid entity, although representing only a subtype of high-frequency OT. A new role may emerge for ¹²³I-FP-CIT SPECT in distinguishing between patients whose symptoms will be restricted to OT throughout the disease course and patients at an increased risk of developing PD.